path: root/doc/rfc/rfc8404.txt

Internet Engineering Task Force (IETF)                  K. Moriarty, Ed.
Request for Comments: 8404                                      Dell EMC
Category: Informational                                   A. Morton, Ed.
ISSN: 2070-1721                                                AT&T Labs
                                                               July 2018


              Effects of Pervasive Encryption on Operators

Abstract

   Pervasive monitoring attacks on the privacy of Internet users are of
   serious concern to both user and operator communities.  RFC 7258
   discusses the critical need to protect users' privacy when developing
   IETF specifications and also recognizes that making networks
   unmanageable to mitigate pervasive monitoring is not an acceptable
   outcome: an appropriate balance is needed.  This document discusses
   current security and network operations as well as management
   practices that may be impacted by the shift to increased use of
   encryption to help guide protocol development in support of
   manageable and secure networks.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It has been approved for publication by the Internet
   Engineering Steering Group (IESG).  Not all documents approved by the
   IESG are candidates for any level of Internet Standard; see Section 2
   of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8404.















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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Additional Background on Encryption Changes . . . . . . .   5
     1.2.  Examples of Attempts to Preserve Functions  . . . . . . .   7
   2.  Network Service Provider Monitoring Practices . . . . . . . .   8
     2.1.  Passive Monitoring  . . . . . . . . . . . . . . . . . . .   8
       2.1.1.  Traffic Surveys . . . . . . . . . . . . . . . . . . .   8
       2.1.2.  Troubleshooting . . . . . . . . . . . . . . . . . . .   9
       2.1.3.  Traffic-Analysis Fingerprinting . . . . . . . . . . .  11
     2.2.  Traffic Optimization and Management . . . . . . . . . . .  12
       2.2.1.  Load Balancers  . . . . . . . . . . . . . . . . . . .  12
       2.2.2.  Differential Treatment Based on Deep Packet
               Inspection (DPI)  . . . . . . . . . . . . . . . . . .  14
       2.2.3.  Network-Congestion Management . . . . . . . . . . . .  16
       2.2.4.  Performance-Enhancing Proxies . . . . . . . . . . . .  16
       2.2.5.  Caching and Content Replication near the Network Edge  17
       2.2.6.  Content Compression . . . . . . . . . . . . . . . . .  18
       2.2.7.  Service Function Chaining . . . . . . . . . . . . . .  18
     2.3.  Content Filtering, Network Access, and Accounting . . . .  19
       2.3.1.  Content Filtering . . . . . . . . . . . . . . . . . .  19
       2.3.2.  Network Access and Data Usage . . . . . . . . . . . .  20
       2.3.3.  Application Layer Gateways (ALGs) . . . . . . . . . .  21
       2.3.4.  HTTP Header Insertion . . . . . . . . . . . . . . . .  22
   3.  Encryption in Hosting and Application SP Environments . . . .  23
     3.1.  Management-Access Security  . . . . . . . . . . . . . . .  23
       3.1.1.  Monitoring Customer Access  . . . . . . . . . . . . .  24
       3.1.2.  SP Content Monitoring of Applications . . . . . . . .  24
     3.2.  Hosted Applications . . . . . . . . . . . . . . . . . . .  26
       3.2.1.  Monitoring Managed Applications . . . . . . . . . . .  27
       3.2.2.  Mail Service Providers  . . . . . . . . . . . . . . .  27
     3.3.  Data Storage  . . . . . . . . . . . . . . . . . . . . . .  28
       3.3.1.  Object-Level Encryption . . . . . . . . . . . . . . .  28



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       3.3.2.  Disk Encryption, Data at Rest (DAR) . . . . . . . . .  29
       3.3.3.  Cross-Data-Center Replication Services  . . . . . . .  29
   4.  Encryption for Enterprises  . . . . . . . . . . . . . . . . .  30
     4.1.  Monitoring Practices of the Enterprise  . . . . . . . . .  30
       4.1.1.  Security Monitoring in the Enterprise . . . . . . . .  31
       4.1.2.  Monitoring Application Performance in the Enterprise   32
       4.1.3.  Diagnostics and Troubleshooting for Enterprise
               Networks  . . . . . . . . . . . . . . . . . . . . . .  33
     4.2.  Techniques for Monitoring Internet-Session Traffic  . . .  34
   5.  Security Monitoring for Specific Attack Types . . . . . . . .  36
     5.1.  Mail Abuse and Spam . . . . . . . . . . . . . . . . . . .  37
     5.2.  Denial of Service . . . . . . . . . . . . . . . . . . . .  37
     5.3.  Phishing  . . . . . . . . . . . . . . . . . . . . . . . .  38
     5.4.  Botnets . . . . . . . . . . . . . . . . . . . . . . . . .  39
     5.5.  Malware . . . . . . . . . . . . . . . . . . . . . . . . .  39
     5.6.  Spoofed-Source IP Address Protection  . . . . . . . . . .  39
     5.7.  Further Work  . . . . . . . . . . . . . . . . . . . . . .  39
   6.  Application-Based Flow Information Visible to a Network . . .  40
     6.1.  IP Flow Information Export  . . . . . . . . . . . . . . .  40
     6.2.  TLS Server Name Indication  . . . . . . . . . . . . . . .  40
     6.3.  Application-Layer Protocol Negotiation (ALPN) . . . . . .  41
     6.4.  Content Length, Bitrate, and Pacing . . . . . . . . . . .  42
   7.  Effect of Encryption on the Evolution of Mobile Networks  . .  42
   8.  Response to Increased Encryption and Looking Forward  . . . .  43
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  43
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  44
   11. Informative References  . . . . . . . . . . . . . . . . . . .  44
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  53
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  53

1.  Introduction

   In response to pervasive monitoring revelations and the IETF
   consensus that pervasive monitoring is an attack [RFC7258], efforts
   are underway to increase encryption of Internet traffic.  Pervasive
   monitoring is of serious concern to users, operators, and application
   providers.  RFC 7258 discusses the critical need to protect users'
   privacy when developing IETF specifications and also recognizes that
   making networks unmanageable to mitigate pervasive monitoring is not
   an acceptable outcome; rather, an appropriate balance would emerge
   over time.

   This document describes practices currently used by network operators
   to manage, operate, and secure their networks and how those practices
   may be impacted by a shift to increased use of encryption.  It
   provides network operators' perspectives about the motivations and
   objectives of those practices as well as effects anticipated by
   operators as use of encryption increases.  It is a summary of



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   concerns of the operational community as they transition to managing
   networks with less visibility.  This document does not endorse the
   use of the practices described herein, nor does it aim to provide a
   comprehensive treatment of the effects of current practices, some of
   which have been considered controversial from a technical or business
   perspectives or contradictory to previous IETF statements (e.g.,
   [RFC1958], [RFC1984], and [RFC2804]).  The following RFCs consider
   the end-to-end (e2e) architectural principle to be a guiding
   principle for the development of Internet protocols [RFC2775]
   [RFC3724] [RFC7754].

   This document aims to help IETF participants understand network
   operators' perspectives about the impact of pervasive encryption,
   both opportunistic and strong end-to-end encryption, on operational
   practices.  The goal is to help inform future protocol development to
   ensure that operational impact is part of the conversation.  Perhaps
   new methods could be developed to accomplish some of the goals of
   current practices despite changes in the extent to which cleartext
   will be available to network operators (including methods that rely
   on network endpoints where applicable).  Discussion of current
   practices and the potential future changes is provided as a
   prerequisite to potential future cross-industry and cross-layer work
   to support the ongoing evolution towards a functional Internet with
   pervasive encryption.

   Traditional network management, planning, security operations, and
   performance optimization have been developed on the Internet where a
   large majority of data traffic flows without encryption.  While
   unencrypted traffic has made information that aids operations and
   troubleshooting at all layers accessible, it has also made pervasive
   monitoring by unseen parties possible.  With broad support and
   increased awareness of the need to consider privacy in all aspects
   across the Internet, it is important to catalog existing management,
   operational, and security practices that have depended upon the
   availability of cleartext to function and to explore if critical
   operational practices can be met by less-invasive means.

   This document refers to several different forms of Service Providers
   (SPs).  For example, network service providers (or network operators)
   provide IP-packet transport primarily, though they may bundle other
   services with packet transport.  Alternatively, application service
   providers primarily offer systems that participate as an endpoint in
   communications with the application user and hosting service
   providers lease computing, storage, and communications systems in
   data centers.  In practice, many companies perform two or more
   service provider roles but may be historically associated with one.





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   This document includes a sampling of current practices and does not
   attempt to describe every nuance.  Some sections cover technologies
   used over a broad spectrum of devices and use cases.

1.1.  Additional Background on Encryption Changes

   Pervasive encryption in this document refers to all types of session
   encryption including Transport Layer Security (TLS), IP Security
   (IPsec), TCPcrypt [TCPcrypt], QUIC [QUIC] (IETF's specification of
   Google's QUIC), and others that are increasingly deployed.  It is
   well understood that session encryption helps to prevent both passive
   and active attacks on transport protocols; more on pervasive
   monitoring can be found in "Confidentiality in the Face of Pervasive
   Surveillance: A Threat Model and Problem Statement" [RFC7624].
   Active attacks have long been a motivation for increased encryption,
   and preventing pervasive monitoring became a focus just a few years
   ago.  As such, the Internet Architecture Board (IAB) released a
   statement advocating for increased use of encryption in November 2014
   (see <https://www.iab.org/2014/11/14/iab-statement-on-internet-
   confidentiality/>).  Perspectives on encryption paradigms have
   shifted over time to make ease of deployment a high priority and to
   balance that against providing the maximum possible level of
   security, regardless of deployment considerations.

   One such shift is documented in Opportunistic Security (OS)
   [RFC7435], which suggests that when use of authenticated encryption
   is not possible, cleartext sessions should be upgraded to
   unauthenticated session encryption, rather than no encryption.  OS
   encourages upgrading from cleartext but cannot require or guarantee
   such upgrades.  Once OS is used, it allows for an evolution to
   authenticated encryption.  These efforts are necessary to improve an
   end user's expectation of privacy, making pervasive monitoring cost
   prohibitive.  With OS in use, active attacks are still possible on
   unauthenticated sessions.  OS has been implemented as NULL
   Authentication with IPsec [RFC7619], and there are a number of
   infrastructure use cases such as server-to-server encryption where
   this mode is deployed.  While OS is helpful in reducing pervasive
   monitoring by increasing the cost to monitor, it is recognized that
   risk profiles for some applications require authenticated and secure
   session encryption as well prevention of active attacks.  IPsec, and
   other session encryption protocols, with authentication has many
   useful applications, and usage has increased for infrastructure
   applications such as for virtual private networks between data
   centers.  OS, as well as other protocol developments like the
   Automated Certificate Management Environment (ACME), have increased
   the usage of session encryption on the Internet.





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   Risk profiles vary and so do the types of session encryption
   deployed.  To understand the scope of changes in visibility, a few
   examples are highlighted.  Work continues to improve the
   implementation, development, and configuration of TLS and DTLS
   sessions to prevent active attacks used to monitor or intercept
   session data.  The changes from TLS 1.2 to 1.3 enhance the security
   of TLS, while hiding more of the session negotiation and providing
   less visibility on the wire.  The Using TLS in Applications (UTA)
   Working Group has been publishing documentation to improve the
   security of TLS and DTLS sessions.  They have documented the known
   attack vectors in [RFC7457], have documented best practices for TLS
   and DTLS in [RFC7525], and have other documents in development.  The
   recommendations from these documents were built upon for TLS 1.3 to
   provide a more inherently secure end-to-end protocol.

   In addition to encrypted website access (HTTP over TLS), there are
   other well-deployed application-level transport encryption efforts
   such as MTA-to-MTA (mail transfer agent) session encryption transport
   for email (SMTP over TLS) and gateway-to-gateway for instant
   messaging (the Extensible Messaging and Presence Protocol (XMPP) over
   TLS).  Although this does provide protection from transport-layer
   attacks, the servers could be a point of vulnerability if user-to-
   user encryption is not provided for these messaging protocols.
   User-to-user content encryption schemes, such as S/MIME and Pretty
   Good Privacy (PGP) for email and Off-the-Record (OTR) encryption for
   XMPP are used by those interested in protecting their data as it
   crosses intermediary servers, preventing transport-layer attacks by
   providing an end-to-end solution.  User-to-user schemes are under
   review, and additional options will emerge to ease the configuration
   requirements, making this type of option more accessible to
   non-technical users interested in protecting their privacy.

   Increased use of encryption, either opportunistic or authenticated,
   at the transport, network, or application layer, impacts how networks
   are operated, managed, and secured.  In some cases, new methods to
   operate, manage, and secure networks will evolve in response.  In
   other cases, currently available capabilities for monitoring or
   troubleshooting networks could become unavailable.  This document
   lists a collection of functions currently employed by network
   operators that may be impacted by the shift to increased use of
   encryption.  This document does not attempt to specify responses or
   solutions to these impacts; it documents the current state.









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1.2.  Examples of Attempts to Preserve Functions

   Following the Snowden [Snowden] revelations, application service
   providers (Yahoo, Google, etc.) responded by encrypting traffic
   between their data centers (IPsec) to prevent passive monitoring from
   taking place unbeknownst to them.  Infrastructure traffic carried
   over the public Internet has been encrypted for some time; this
   change for universal encryption was specific to their private
   backbones.  Large mail service providers also began to encrypt
   session transport (TLS) to hosted mail services.  This and other
   increases in the use of encryption had the immediate effect of
   providing confidentiality and integrity for protected data, but it
   created a problem for some network-management functions.  Operators
   could no longer gain access to some session streams resulting in
   actions by several to regain their operational practices that
   previously depended on cleartext data sessions.

   The Electronic Frontier Foundation (EFF) reported [EFF2014] several
   network service providers using a downgrade attack to prevent the use
   of SMTP over TLS by breaking STARTTLS (Section 3.2 of [RFC7525]),
   essentially preventing the negotiation process resulting in fallback
   to the use of cleartext.  There have already been documented cases of
   service providers preventing STARTTLS to avoid session encryption
   negotiation on some sessions.  Doing so allows them to inject a super
   cookie that enables advertisers to track users; these actions are
   also considered an attack.  These serve as examples of undesirable
   behavior that could be prevented through upfront discussions in
   protocol work for operators and protocol designers to understand the
   implications of such actions.  In other cases, some service providers
   and enterprises have relied on middleboxes having access to cleartext
   for load-balancing, monitoring for attack traffic, meeting regulatory
   requirements, or other purposes.  The implications for enterprises
   that own the data on their networks or that have explicit agreements
   that permit the monitoring of user traffic are very different from
   those for service providers who may be accessing content in a way
   that violates privacy considerations.  Additionally, service provider
   equipment is designed for accessing only the headers exposed for the
   data-link, network, and transport layers.  Delving deeper into
   packets is possible, but there is typically a high degree of accuracy
   from the header information and packet sizes when limited to header
   information from these three layers.  Service providers also have the
   option of adding routing overlay protocols to traffic.  These
   middlebox implementations, performing functions either considered
   legitimate by the IETF or not, have been impacted by increases in
   encrypted traffic.  Only methods keeping with the goal of balancing
   network management and pervasive monitoring mitigation as discussed
   in [RFC7258] should be considered in work toward a solution resulting
   from this document.



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   It is well known that national surveillance programs monitor traffic
   for criminal activities [JNSLP] [RFC2804] [RFC7258].  Governments
   vary on their balance between monitoring versus the protection of
   user privacy, data, and assets.  Those that favor unencrypted access
   to data ignore the real need to protect users' identities, financial
   transactions, and intellectual property (which require security and
   encryption to prevent crime).  A clear understanding of technology,
   encryption, and monitoring goals will aid in the development of
   solutions as work continues towards finding an appropriate balance
   that allows for management while protecting user privacy with strong
   encryption solutions.

2.  Network Service Provider Monitoring Practices

   Service providers, for this definition, include the backbone ISPs as
   well as those providing infrastructure at scale for core Internet use
   (hosted infrastructure and services such as email).

   Network service providers use various techniques to operate, manage,
   and secure their networks.  The following subsections detail the
   purpose of several techniques as well as which protocol fields are
   used to accomplish each task.  In response to increased encryption of
   these fields, some network service providers may be tempted to
   undertake undesirable security practices in order to gain access to
   the fields in unencrypted data flows.  To avoid this situation, new
   methods could be developed to accomplish the same goals without
   service providers having the ability to see session data.

2.1.  Passive Monitoring

2.1.1.  Traffic Surveys

   Internet traffic surveys are useful in many pursuits, such as input
   for studies of the Center for Applied Internet Data Analysis (CAIDA)
   [CAIDA], network planning, and optimization.  Tracking the trends in
   Internet traffic growth, from earlier peer-to-peer communication to
   the extensive adoption of unicast video streaming applications, has
   relied on a view of traffic composition with a particular level of
   assumed accuracy, based on access to cleartext by those conducting
   the surveys.

   Passive monitoring makes inferences about observed traffic using the
   maximal information available and is subject to inaccuracies stemming
   from incomplete sampling (of packets in a stream) or loss due to
   monitoring-system overload.  When encryption conceals more layers in
   each packet, reliance on pattern inferences and other heuristics
   grows and accuracy suffers.  For example, the traffic patterns
   between server and browser are dependent on browser supplier and



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   version, even when the sessions use the same server application
   (e.g., web email access).  It remains to be seen whether more complex
   inferences can be mastered to produce the same monitoring accuracy.

2.1.2.  Troubleshooting

   Network operators use protocol-dissecting analyzers when responding
   to customer problems, to identify the presence of attack traffic, and
   to identify root causes of the problem such as misconfiguration.  In
   limited cases, packet captures may also be used when a customer
   approves of access to their packets or provides packet captures close
   to the endpoint.  The protocol dissection is generally limited to
   supporting protocols (e.g., DNS and DHCP), network and transport
   (e.g., IP and TCP), and some higher-layer protocols (e.g., RTP and
   the RTP Control Protocol (RTCP)).  Troubleshooting will move closer
   to the endpoint with increased encryption and adjustments in
   practices to effectively troubleshoot using a 5-tuple may require
   education.  Packet-loss investigations, and those where access is
   limited to a 2-tuple (IPsec tunnel mode), rely on network and
   transport-layer headers taken at the endpoint.  In this case,
   captures on intermediate nodes are not reliable as there are far too
   many cases of aggregate interfaces and alternate paths in service
   provider networks.

   Network operators are often the first ones called upon to investigate
   application problems (e.g., "my HD video is choppy"), to first rule
   out network and network services as a cause for the underlying issue.
   When diagnosing a customer problem, the starting point may be a
   particular application that isn't working.  The ability to identify
   the problem application's traffic is important, and packet capture
   provided from the customer close to the edge may be used for this
   purpose; IP address filtering is not useful for applications using
   Content Delivery Networks (CDNs) or cloud providers.  After
   identifying the traffic, an operator may analyze the traffic
   characteristics and routing of the traffic.  This diagnostic step is
   important to help determine the root cause before exploring if the
   issue is directly with the application.

   For example, by investigating packet loss (from TCP sequence and
   acknowledgement numbers), Round-Trip Time (RTT) (from TCP timestamp
   options or application-layer transactions, e.g., DNS or HTTP response
   time), TCP receive-window size, packet corruption (from checksum
   verification), inefficient fragmentation, or application-layer
   problems, the operator can narrow the problem to a portion of the
   network, server overload, client or server misconfiguration, etc.
   Network operators may also be able to identify the presence of attack





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   traffic as not conforming to the application the user claims to be
   using.  In many instances, the exposed packet header is sufficient
   for this type of troubleshooting.

   One way of quickly excluding the network as the bottleneck during
   troubleshooting is to check whether the speed is limited by the
   endpoints.  For example, the connection speed might instead be
   limited by suboptimal TCP options, the sender's congestion window,
   the sender temporarily running out of data to send, the sender
   waiting for the receiver to send another request, or the receiver
   closing the receive window.  All this information can be derived from
   the cleartext TCP header.

   Packet captures and protocol-dissecting analyzers have been important
   tools.  Automated monitoring has also been used to proactively
   identify poor network conditions, leading to maintenance and network
   upgrades before user experience declines.  For example, findings of
   loss and jitter in Voice over IP (VoIP) traffic can be a predictor of
   future customer dissatisfaction (supported by metadata from RTP/RTCP)
   [RFC3550], or increases in DNS response time can generally make
   interactive web browsing appear sluggish.  But, to detect such
   problems, the application or service stream must first be
   distinguished from others.

   When increased encryption is used, operators lose a source of data
   that may be used to debug user issues.  For example, IPsec obscures
   TCP and RTP header information, while TLS and the Secure Real-time
   Transport Protocol (SRTP) do not.  Because of this, application-
   server operators using increased encryption might be called upon more
   frequently to assist with debugging and troubleshooting; thus, they
   may want to consider what tools can be put in the hands of their
   clients or network operators.

   Further, the performance of some services can be more efficiently
   managed and repaired when information on user transactions is
   available to the service provider.  It may be possible to continue
   transaction-monitoring activities without cleartext access to the
   application layers of interest; however, inaccuracy will increase and
   efficiency of repair activities will decrease.  For example, an
   application-protocol error or failure would be opaque to network
   troubleshooters when transport encryption is applied, making root
   cause location more difficult and, therefore, increasing the time to
   repair.  Repair time directly reduces the availability of the
   service, and most network operators have made availability a key
   metric in their Service Level Agreements (SLAs) and/or subscription
   rebates.  Also, there may be more cases of user-communication
   failures when the additional encryption processes are introduced
   (e.g., key management at large scale), leading to more customer



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   service contacts and (at the same time) less information available to
   network-operation repair teams.

   In mobile networks, knowledge about TCP's stream transfer progress
   (by observing ACKs, retransmissions, packet drops, and the Sector
   Utilization Level, etc.) is further used to measure the performance
   of network segments (sector, eNodeB (eNB), etc.).  This information
   is used as key performance indicators (KPIs) and for the estimation
   of user/service key quality indicators at network edges for circuit
   emulation (CEM) as well as input for mitigation methods.  If the
   makeup of active services per user and per sector are not visible to
   a server that provides Internet Access Point Names (APNs), it cannot
   perform mitigation functions based on network segment view.

   It is important to note that the push for encryption by application
   providers has been motivated by the application of the described
   techniques.  Although network operators have noted performance
   improvements with network-based optimization or enhancement of user
   traffic (otherwise, deployment would not have occurred), application
   providers have likewise noted some degraded performance and/or user
   experience, and such cases may result in additional operator
   troubleshooting.  Further, encrypted application streams might avoid
   outdated optimization or enhancement techniques, where they exist.

   A gap exists for vendors where built-in diagnostics and
   serviceability are not adequate to provide detailed logging and
   debugging capabilities that, when possible, could be accessed with
   cleartext network parameters.  In addition to traditional logging and
   debugging methods, packet tracing and inspection along the service
   path provides operators the visibility to continue to diagnose
   problems reported both internally and by their customers.  Logging of
   service path upon exit for routing overlay protocols will assist with
   policy management and troubleshooting capabilities for traffic flows
   on encrypted networks.  Protocol trace logging and protocol data unit
   (PDU) logging should also be considered to improve visibility to
   monitor and troubleshoot application-level traffic.  Additional work
   on this gap would assist network operators to better troubleshoot and
   manage networks with increasing amounts of encrypted traffic.

2.1.3.  Traffic-Analysis Fingerprinting

   Fingerprinting is used in traffic analysis and monitoring to identify
   traffic streams that match certain patterns.  This technique can be
   used with both cleartext and encrypted sessions.  Some Distributed
   Denial-of-Service (DDoS) prevention techniques at the network-
   provider level rely on the ability to fingerprint traffic in order to
   mitigate the effect of this type of attack.  Thus, fingerprinting may
   be an aspect of an attack or part of attack countermeasures.



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   A common, early trigger for DDoS mitigation includes observing
   uncharacteristic traffic volumes or sources, congestion, or
   degradation of a given network or service.  One approach to mitigate
   such an attack involves distinguishing attacker traffic from
   legitimate user traffic.  The ability to examine layers and payloads
   above transport provides an increased range of filtering
   opportunities at each layer in the clear.  If fewer layers are in the
   clear, this means that there are reduced filtering opportunities
   available to mitigate attacks.  However, fingerprinting is still
   possible.

   Passive monitoring of network traffic can lead to invasion of privacy
   by external actors at the endpoints of the monitored traffic.
   Encryption of traffic end to end is one method to obfuscate some of
   the potentially identifying information.  For example, browser
   fingerprints are comprised of many characteristics, including User
   Agents, HTTP Accept headers, browser plug-in details, screen size and
   color details, system fonts, and time zones.  A monitoring system
   could easily identify a specific browser, and by correlating other
   information, identify a specific user.

2.2.  Traffic Optimization and Management

2.2.1.  Load Balancers

   A standalone load balancer is a function one can take off the shelf,
   place in front of a pool of servers, and configure appropriately, and
   it will balance the traffic load among servers in the pool.  This is
   a typical setup for load balancers.  Standalone load balancers rely
   on the plainly observable information in the packets they are
   forwarding and industry-accepted standards in interpreting the
   plainly observable information.  Typically, this is a 5-tuple of the
   connection.  This type of configuration terminates TLS sessions at
   the load balancer, making it the endpoint instead of the server.
   Standalone load balancers are considered middleboxes, but they are an
   integral part of server infrastructure that scales.

   In contrast, an integrated load balancer is developed to be an
   integral part of the service provided by the server pool behind that
   load balancer.  These load balancers can communicate state with their
   pool of servers to better route flows to the appropriate servers.
   They rely on non-standard, system-specific information and
   operational knowledge shared between the load balancer and its
   servers.

   Both standalone and integrated load balancers can be deployed in
   pools for redundancy and load sharing.  For high availability, it is
   important that when packets belonging to a flow start to arrive at a



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   different load balancer in the load-balancer pool, the packets
   continue to be forwarded to the original server in the server pool.
   The importance of this requirement increases as the chance of such a
   load balancer change event increases.

   Mobile operators deploy integrated load balancers to assist with
   maintaining connection state as devices migrate.  With the
   proliferation of mobile connected devices, there is an acute need for
   connection-oriented protocols that maintain connections after a
   network migration by an endpoint.  This connection persistence
   provides an additional challenge for multihomed anycast-based
   services typically employed by large content owners and CDNs.  The
   challenge is that a migration to a different network in the middle of
   the connection greatly increases the chances of the packets routed to
   a different anycast point of presence (POP) due to the new network's
   different connectivity and Internet peering arrangements.  The load
   balancer in the new POP, potentially thousands of miles away, will
   not have information about the new flow and would not be able to
   route it back to the original POP.

   To help with the endpoint network migration challenges, anycast
   service operations are likely to employ integrated load balancers
   that, in cooperation with their pool servers, are able to ensure that
   client-to-server packets contain some additional identification in
   plainly observable parts of the packets (in addition to the 5-tuple).
   As noted in Section 2 of [RFC7258], careful consideration in protocol
   design to mitigate pervasive monitoring is important, while ensuring
   manageability of the network.

   An area for further research includes end-to-end solutions that would
   provide a simpler architecture and that may solve the issue with CDN
   anycast.  In this case, connections would be migrated to a CDN
   unicast address.

   Current protocols, such as TCP, allow the development of stateless
   integrated load balancers by availing such load balancers of
   additional plaintext information in client-to-server packets.  In
   case of TCP, such information can be encoded by having server-
   generated sequence numbers (that are ACKed by the client), segment
   values, lengths of the packet sent, etc.  The use of some of these
   mechanisms for load balancing negates some of the security
   assumptions associated with those primitives (e.g., that an off-path
   attacker guessing valid sequence numbers for a flow is hard).
   Another possibility is a dedicated mechanism for storing load-
   balancer state, such as QUIC's proposed connection ID to provide
   visibility to the load balancer.  An identifier could be used for
   tracking purposes, but this may provide an option that is an
   improvement from bolting it on to an unrelated transport signal.



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   This method allows for tight control by one of the endpoints and can
   be rotated to avoid roving client linkability: in other words, being
   a specific, separate signal, it can be governed in a way that is
   finely targeted at that specific use case.

   Some integrated load balancers have the ability to use additional
   plainly observable information even for today's protocols that are
   not network-migration tolerant.  This additional information allows
   for improved availability and scalability of the load-balancing
   operation.  For example, BGP reconvergence can cause a flow to switch
   anycast POPs, even without a network change by any endpoint.
   Additionally, a system that is able to encode the identity of the
   pool server in plaintext information available in each incoming
   packet is able to provide stateless load balancing.  This ability
   confers great reliability and scalability advantages, even if the
   flow remains in a single POP, because the load-balancing system is
   not required to keep state of each flow.  Even more importantly,
   there's no requirement to continuously synchronize such state among
   the pool of load balancers.  An integrated load balancer repurposing
   limited existing bits in transport-flow state must maintain and
   synchronize per-flow state occasionally: using the sequence number as
   a cookie only works for so long given that there aren't that many
   bits available to divide across a pool of machines.

   Mobile operators apply 3GPP Self-Organizing Networks (SONs) for
   intelligent workflows such as content-aware Mobility Load Balancing
   (MLB).  Where network load balancers have been configured to route
   according to application-layer semantics, an encrypted payload is
   effectively invisible.  This has resulted in practices of
   intercepting TLS in front of load balancers to regain that
   visibility, but at a cost to security and privacy.

   In future Network Function Virtualization (NFV) architectures, load-
   balancing functions are likely to be more prevalent (deployed at
   locations throughout operators' networks).  NFV environments will
   require some type of identifier (IPv6 flow identifiers, the proposed
   QUIC connection ID, etc.) for managing traffic using encrypted
   tunnels.  The shift to increased encryption will have an impact on
   visibility of flow information and will require adjustments to
   perform similar load-balancing functions within an NFV.

2.2.2.  Differential Treatment Based on Deep Packet Inspection (DPI)

   Data transfer capacity resources in cellular radio networks tend to
   be more constrained than in fixed networks.  This is a result of
   variance in radio signal strength as a user moves around a cell, the
   rapid ingress and egress of connections as users hand off between
   adjacent cells, and temporary congestion at a cell.  Mobile networks



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   alleviate this by queuing traffic according to its required bandwidth
   and acceptable latency: for example, a user is unlikely to notice a
   20 ms delay when receiving a simple web page or email, or an instant
   message response, but will very likely notice a rebuffering pause in
   a video playback or a VoIP call de-jitter buffer.  Ideally, the
   scheduler manages the queue so that each user has an acceptable
   experience as conditions vary, but inferences of the traffic type
   have been used to make bearer assignments and set scheduler priority.

   Deep Packet Inspection (DPI) allows identification of applications
   based on payload signatures, in contrast to trusting well-known port
   numbers.  Application- and transport-layer encryption make the
   traffic type estimation more complex and less accurate; therefore, it
   may not be effectual to use this information as input for queue
   management.  With the use of WebSockets [RFC6455], for example, many
   forms of communications (from isochronous/real-time to bulk/elastic
   file transfer) will take place over HTTP port 80 or port 443, so only
   the messages and higher-layer data will make application
   differentiation possible.  If the monitoring system sees only "HTTP
   port 443", it cannot distinguish application streams that would
   benefit from priority queuing from others that would not.

   Mobile networks especially rely on content-/application-based
   prioritization of Over-the-Top (OTT) services -- each application
   type or service has different delay/loss/throughput expectations, and
   each type of stream will be unknown to an edge device if encrypted.
   This impedes dynamic QoS adaptation.  An alternate way to achieve
   encrypted application separation is possible when the User Equipment
   (UE) requests a dedicated bearer for the specific application stream
   (known by the UE), using a mechanism such as the one described in
   Section 6.5 of 3GPP TS 24.301 [TS3GPP].  The UE's request includes
   the Quality Class Indicator (QCI) appropriate for each application,
   based on their different delay/loss/throughput expectations.
   However, UE requests for dedicated bearers and QCI may not be
   supported at the subscriber's service level, or in all mobile
   networks.

   These effects and potential alternative solutions have been discussed
   at the accord BoF [ACCORD] at IETF 95.

   This section does not consider traffic discrimination by service
   providers related to Net Neutrality, where traffic may be favored
   according to the service provider's preference as opposed to the
   user's preference.  These use cases are considered out of scope for
   this document as controversial practices.






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2.2.3.  Network-Congestion Management

   For 3GPP User Plane Congestion Management (UPCON) [UPCON], the
   ability to understand content and manage networks during periods of
   congestion is the focus.  Mitigating techniques such as deferred
   download, off-peak acceleration, and outbound roamers are a few
   examples of the areas explored in the associated 3GPP documents.  The
   documents describe the issues, describe the data utilized in managing
   congestion, and make policy recommendations.

2.2.4.  Performance-Enhancing Proxies

   Performance-enhancing TCP proxies may perform local retransmission at
   the network edge; this also applies to mobile networks.  In TCP,
   duplicated ACKs are detected and potentially concealed when the proxy
   retransmits a segment that was lost on the mobile link without
   involvement of the far end (see Section 2.1.1 of [RFC3135] and
   Section 3.5 of [MIDDLEBOXES]).

   Operators report that this optimization at network edges improves
   real-time transmission over long-delay Internet paths or networks
   with large capacity variation (such as mobile/cellular networks).
   However, such optimizations can also cause problems with performance,
   for example, if the characteristics of some packet streams begin to
   vary significantly from those considered in the proxy design.

   In general, some operators have stated that performance-enhancing
   proxies have a lower RTT to the client; therefore, they determine the
   responsiveness of flow control.  A lower RTT makes the flow-control
   loop more responsive to changes in the mobile-network conditions and
   enables faster adaptation in a delay- and capacity-varying network
   due to user mobility.

   Further, some use service-provider-operated proxies to reduce the
   control delay between the sender and a receiver on a mobile network
   where resources are limited.  The RTT determines how quickly a user's
   attempt to cancel a video is recognized and, therefore, how quickly
   the traffic is stopped, thus keeping unwanted video packets from
   entering the radio-scheduler queue.  If impacted by encryption,
   performance-enhancing proxies could make use of routing overlay
   protocols to accomplish the same task, but this results in additional
   overhead.

   An application-type-aware network edge (middlebox) can further
   control pacing, limit simultaneous HD videos, or prioritize active
   videos against new videos, etc.  Services at this more granular level
   are limited with the use of encryption.




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   Performance-enhancing proxies are primarily used on long-delay links
   (satellite) with access to the TCP header to provide an early ACK and
   make the long-delay link of the path seem shorter.  With some
   specific forms of flow control, TCP can be more efficient than
   alternatives such as proxies.  The editors cannot cite research on
   this point specific to the performance-enhancing proxies described,
   but they agree this area could be explored to determine if flow-
   control modifications could preserve the end-to-end performance on
   long-delay path sessions where the TCP header is exposed.

2.2.5.  Caching and Content Replication near the Network Edge

   The features and efficiency of some Internet services can be
   augmented through analysis of user flows and the applications they
   provide.  For example, network caching of popular content at a
   location close to the requesting user can improve delivery efficiency
   (both in terms of lower request response times and reduced use of
   links on the international Internet when content is remotely
   located), and service providers through an authorized agreement
   acting on their behalf use DPI in combination with content-
   distribution networks to determine if they can intervene effectively.
   Encryption of packet contents at a given protocol layer usually makes
   DPI processing of that layer and higher layers impossible.  That
   being said, it should be noted that some content providers prevent
   caching to control content delivery through the use of encrypted
   end-to-end sessions.  CDNs vary in their deployment options of end-
   to-end encryption.  The business risk of losing control of content is
   a motivation outside of privacy and pervasive monitoring that is
   driving end-to-end encryption for these content providers.

   It should be noted that caching was first supported in [RFC1945] and
   continued in the recent update of "Hypertext Transfer Protocol
   (HTTP/1.1): Caching" [RFC7234].  Some operators also operate
   transparent caches that neither the user nor the origin opt-in.  The
   use of these caches is controversial within the IETF and is generally
   precluded by the use of HTTPS.

   Content replication in caches (for example, live video and content
   protected by Digital Rights Management (DRM)) is used to most
   efficiently utilize the available limited bandwidth and thereby
   maximize the user's Quality of Experience (QoE).  Especially in
   mobile networks, duplicating every stream through the transit network
   increases backhaul cost for live TV. 3GPP Enhanced Multimedia
   Broadcast/Multicast Services (eMBMS) utilize trusted edge proxies to
   facilitate delivering the same stream to different users, using
   either unicast or multicast depending on channel conditions to the
   user.  There are ongoing efforts to support multicast inside carrier
   networks while preserving end-to-end security: Automatic Multicast



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   Tunneling (AMT), for instance, allows CDNs to deliver a single
   (potentially encrypted) copy of a live stream to a carrier network
   over the public Internet and for the carrier to then distribute that
   live stream as efficiently as possible within its own network using
   multicast.

   Alternate approaches are in the early phase of being explored to
   allow caching of encrypted content.  These solutions require
   cooperation from content owners and fall outside the scope of what is
   covered in this document.  Content delegation allows for replication
   with possible benefits, but any form of delegation has the potential
   to affect the expectation of client-server confidentiality.

2.2.6.  Content Compression

   In addition to caching, various applications exist to provide data
   compression in order to conserve the life of the user's mobile data
   plan or make delivery over the mobile link more efficient.  The
   compression proxy access can be built into a specific user-level
   application, such as a browser, or it can be available to all
   applications using a system-level application.  The primary method is
   for the mobile application to connect to a centralized server as a
   transparent proxy (user does not opt-in), with the data channel
   between the client application and the server using compression to
   minimize bandwidth utilization.  The effectiveness of such systems
   depends on the server having access to unencrypted data flows.

   Aggregated data stream content compression that spans objects and
   data sources that can be treated as part of a unified compression
   scheme (e.g., through the use of a shared segment store) is often
   effective at providing data offload when there is a network element
   close to the receiver that has access to see all the content.

2.2.7.  Service Function Chaining

   Service Function Chaining (SFC) is defined in RFC 7665 [RFC7665] and
   RFC 8300 [RFC8300].  As discussed in RFC 7498 [RFC7498], common SFC
   deployments may use classifiers to direct traffic into VLANs instead
   of using a Network Service Header (NSH), as defined in RFC 8300
   [RFC8300].  As described in RFC 7665 [RFC7665], the ordered steering
   of traffic to support specific optimizations depends upon the ability
   of a classifier to determine the microflows.  RFC 2474 [RFC2474]
   defines the following:

      Microflow: a single instance of an application-to-application flow
      of packets which is identified by source address, destination
      address, protocol id, and source port, destination port (where
      applicable).



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   SFC currently depends upon a classifier to at least identify the
   microflow.  As the classifier's visibility is reduced from a 5-tuple
   to a 2-tuple, or if information above the transport layer becomes
   inaccessible, then the SFC classifier is not able to perform its job,
   and the service functions of the path may be adversely affected.

   There are also mechanisms provided to protect security and privacy.
   In the SFC case, the layer below a network service header can be
   protected with session encryption.  A goal is protecting end-user
   data, while retaining the intended functions of RFC 7665 [RFC7665] at
   the same time.

2.3.  Content Filtering, Network Access, and Accounting

   Mobile networks and many ISPs operate under the regulations of their
   licensing government authority.  These regulations include Lawful
   Intercept, adherence to Codes of Practice on content filtering, and
   application of court order filters.  Such regulations assume network
   access to provide content filtering and accounting, as discussed
   below.  As previously stated, the intent of this document is to
   document existing practices; the development of IETF protocols
   follows the guiding principles of [RFC1984] and [RFC2804] and
   explicitly does not support tools and methods that could be used for
   wiretapping and censorship.

2.3.1.  Content Filtering

   There are numerous reasons why service providers might block content:
   to comply with requests from law enforcement or regulatory
   authorities, to effectuate parental controls, to enforce content-
   based billing, or for other reasons, possibly considered
   inappropriate by some.  See RFC 7754 [RFC7754] for a survey of
   Internet filtering techniques and motivations and the IAB consensus
   on those mechanisms.  This section is intended to document a
   selection of current content-blocking practices by operators and the
   effects of encryption on those practices.  Content blocking may also
   happen at endpoints or at the edge of enterprise networks, but those
   scenarios are not addressed in this section.

   In a mobile network, content filtering usually occurs in the core
   network.  With other networks, content filtering could occur in the
   core network or at the edge.  A proxy is installed that analyzes the
   transport metadata of the content users are viewing and filters
   content based on either a blacklist of sites or the user's predefined
   profile (e.g., for age-sensitive content).  Although filtering can be
   done by many methods, one commonly used method involves a trigger
   based on the proxy identifying a DNS lookup of a host name in a URL
   that appears on a blacklist being used by the operator.  The



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   subsequent requests to that domain will be rerouted to a proxy that
   checks whether the full URL matches a blocked URL on the list, and it
   will return a 404 if a match is found.  All other requests should
   complete.  This technique does not work in situations where DNS
   traffic is encrypted (e.g., by employing [RFC7858]).  This method is
   also used by other types of network providers enabling traffic
   inspection, but not modification.

   Content filtering via a proxy can also utilize an intercepting
   certificate where the client's session is terminated at the proxy
   enabling for cleartext inspection of the traffic.  A new session is
   created from the intercepting device to the client's destination;
   this is an opt-in strategy for the client, where the endpoint is
   configured to trust the intercepting certificate.  Changes to TLS 1.3
   do not impact this more invasive method of interception, which has
   the potential to expose every HTTPS session to an active man in the
   middle (MITM).

   Another form of content filtering is called parental control, where
   some users are deliberately denied access to age-sensitive content as
   a feature to the service subscriber.  Some sites involve a mixture of
   universal and age-sensitive content and filtering software.  In these
   cases, more-granular (application-layer) metadata may be used to
   analyze and block traffic.  Methods that accessed cleartext
   application-layer metadata no longer work when sessions are
   encrypted.  This type of granular filtering could occur at the
   endpoint or as a proxy service.  However, the lack of ability to
   efficiently manage endpoints as a service reduces network service
   providers' ability to offer parental control.

2.3.2.  Network Access and Data Usage

   Approved access to a network is a prerequisite to requests for
   Internet traffic.

   However, there are cases (beyond parental control) when a network
   service provider currently redirects customer requests for content
   (affecting content accessibility):

   1.  The network service provider is performing the accounting and
       billing for the content provider, and the customer has not (yet)
       purchased the requested content.

   2.  Further content may not be allowed as the customer has reached
       their usage limit and needs to purchase additional data service,
       which is the usual billing approach in mobile networks.





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   Currently, some network service providers redirect the customer using
   HTTP redirect to a captive portal page that explains to those
   customers the reason for the blockage and the steps to proceed.
   [RFC6108] describes one viable web notification system.  When the
   HTTP headers and content are encrypted, this appropriately prevents
   mobile carriers from intercepting the traffic and performing an HTTP
   redirect.  As a result, some mobile carriers block customer's
   encrypted requests, which impacts customer experience because the
   blocking reason must be conveyed by some other means.  The customer
   may need to call customer care to find out the reason and/or resolve
   the issue, possibly extending the time needed to restore their
   network access.  While there are well-deployed alternate SMS-based
   solutions that do not involve out-of-specification protocol
   interception, this is still an unsolved problem for non-SMS users.

   Further, when the requested service is about to consume the remainder
   of the user's plan limits, the transmission could be terminated and
   advance notifications may be sent to the user by their service
   provider to warn the user ahead of the exhausted plan.  If web
   content is encrypted, the network provider cannot know the data
   transfer size at request time.  Lacking this visibility of the
   application type and content size, the network would continue the
   transmission and stop the transfer when the limit was reached.  A
   partial transfer may not be usable by the client wasting both network
   and user resources, possibly leading to customer complaints.  The
   content provider does not know a user's service plans or current
   usage and cannot warn the user of plan exhaustion.

   In addition, some mobile network operators sell tariffs that allow
   free-data access to certain sites, known as 'zero rating'.  A session
   to visit such a site incurs no additional cost or data usage to the
   user.  For some implementations, zero rating is impacted if
   encryption hides the details of the content domain from the network.

2.3.3.  Application Layer Gateways (ALGs)

   Application Layer Gateways (ALGs) assist applications to set
   connectivity across Network Address Translators (NATs), firewalls,
   and/or load balancers for specific applications running across mobile
   networks.  Section 2.9 of [RFC2663] describes the role of ALGs and
   their interaction with NAT and/or application payloads.  ALGs are
   deployed with an aim to improve connectivity.  However, it is an IETF
   best common practice recommendation that ALGs for UDP-based protocols
   be turned off [RFC4787].







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   One example of an ALG in current use is aimed at video applications
   that use the Real-Time Streaming Protocol (RTSP) [RFC7826] primary
   stream as a means to identify related RTP/RTCP [RFC3550] flows at
   setup.  The ALG in this case relies on the 5-tuple flow information
   derived from RTSP to provision NAT or other middleboxes and provide
   connectivity.  Implementations vary, and two examples follow:

   1.  Parse the content of the RTSP stream and identify the 5-tuple of
       the supporting streams as they are being negotiated.

   2.  Intercept and modify the 5-tuple information of the supporting
       media streams as they are being negotiated on the RTSP stream,
       which is more intrusive to the media streams.

   When RTSP-stream content is encrypted, the 5-tuple information within
   the payload is not visible to these ALG implementations; therefore,
   they cannot provision their associated middleboxes with that
   information.

   The deployment of IPv6 may well reduce the need for NAT and the
   corresponding requirement for ALGs.

2.3.4.  HTTP Header Insertion

   Some mobile carriers use HTTP header insertion (see Section 3.2.1 of
   [RFC7230]) to provide information about their customers to third
   parties or to their own internal systems [Enrich].  Third parties use
   the inserted information for analytics, customization, advertising,
   cross-site tracking of users, customer billing, or selectively
   allowing or blocking content.  HTTP header insertion is also used to
   pass information internally between a mobile service provider's
   sub-systems, thus keeping the internal systems loosely coupled.  When
   HTTP connections are encrypted to protect user privacy, mobile
   network service providers cannot insert headers to accomplish the,
   sometimes considered controversial, functions above.

   Guidance from the Internet Architecture Board has been provided in
   "Design Considerations for Metadata Insertion" [RFC8165].  The
   guidance asserts that designs that share metadata only by explicit
   actions at the host are preferable to designs in which middleboxes
   insert metadata.  Alternate notification methods that follow this and
   other guidance would be helpful to mobile carriers.









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3.  Encryption in Hosting and Application SP Environments

   Hosted environments have had varied requirements in the past for
   encryption, with many businesses choosing to use these services
   primarily for data and applications that are not business or privacy
   sensitive.  A shift prior to the revelations on surveillance/passive
   monitoring began where businesses were asking for hosted environments
   to provide higher levels of security so that additional applications
   and service could be hosted externally.  Businesses understanding the
   threats of monitoring in hosted environments increased that pressure
   to provide more secure access and session encryption to protect the
   management of hosted environments as well as the data and
   applications.

3.1.  Management-Access Security

   Hosted environments may have multiple levels of management access,
   where some may be strictly for the Hosting service provider
   (infrastructure that may be shared among customers), and some may be
   accessed by a specific customer for application management.  In some
   cases, there are multiple levels of hosting service providers,
   further complicating the security of management infrastructure and
   the associated requirements.

   Hosting service provider management access is typically segregated
   from other traffic with a control channel and may or may not be
   encrypted depending upon the isolation characteristics of the
   management session.  Customer access may be through a dedicated
   connection, but discussion for that connection method is out of scope
   for this document.

   In overlay networks (e.g., Virtual eXtensible Local Area Network
   (VXLAN), Geneve, etc.) that are used to provide hosted services,
   management access for a customer to support application management
   may depend upon the security mechanisms available as part of that
   overlay network.  While overlay-network data encapsulations may be
   used to indicate the desired isolation, this is not sufficient to
   prevent deliberate attacks that are aware of the use of the overlay
   network.  [GENEVE-REQS] describes requirements to handle attacks.  It
   is possible to use an overlay header in combination with IPsec or
   other encrypted traffic sessions, but this adds the requirement for
   authentication infrastructure and may reduce packet transfer
   performance.  The use of an overlay header may also be deployed as a
   mechanism to manage encrypted traffic streams on the network-by-
   network service providers.  Additional extension mechanisms to
   provide integrity and/or privacy protections are being investigated
   for overlay encapsulations.  Section 7 of [RFC7348] describes some of




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   the security issues possible when deploying VXLAN on Layer 2
   networks.  Rogue endpoints can join the multicast groups that carry
   broadcast traffic, for example.

3.1.1.  Monitoring Customer Access

   Hosted applications that allow some level of customer-management
   access may also require monitoring by the hosting service provider.
   Monitoring could include access-control restrictions such as
   authentication, authorization, and accounting for filtering and
   firewall rules to ensure they are continuously met.  Customer access
   may occur on multiple levels, including user-level and administrative
   access.  The hosting service provider may need to monitor access
   through either session monitoring or log evaluation to ensure
   security SLAs for access management are met.  The use of session
   encryption to access hosted environments limits access restrictions
   to the metadata described below.  Monitoring and filtering may occur
   at a:

   2-tuple:  IP level with source and destination IP addresses alone, or

   5-tuple:  IP and protocol level with a source IP address, destination
      IP address, protocol number, source port number, and destination
      port number.

   Session encryption at the application level, for example, TLS,
   currently allows access to the 5-tuple.  IP-level encryption, such as
   IPsec in tunnel mode, prevents access to the original 5-tuple and may
   limit the ability to restrict traffic via filtering techniques.  This
   shift may not impact all hosting service provider solutions as
   alternate controls may be used to authenticate sessions, or access
   may require that clients access such services by first connecting to
   the organization before accessing the hosted application.  Shifts in
   access may be required to maintain equivalent access-control
   management.  Logs may also be used for monitoring that access-control
   restrictions are met, but would be limited to the data that could be
   observed due to encryption at the point of log generation.  Log
   analysis is out of scope for this document.

3.1.2.  SP Content Monitoring of Applications

   The following observations apply to any IT organization that is
   responsible for delivering services, whether to third parties, for
   example, as a web-based service, or to internal customers in an
   enterprise, e.g., a data-processing system that forms a part of the
   enterprise's business.





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   Organizations responsible for the operation of a data center have
   many processes that access the contents of IP packets (passive
   methods of measurement, as defined in [RFC7799]).  These processes
   are typically for service assurance or security purposes as part of
   their data-center operations.

   Examples include:

      - Network-Performance Monitoring / Application-Performance
        Monitoring

      - Intrusion defense/prevention systems

      - Malware detection

      - Fraud monitoring

      - Application DDOS protection

      - Cyber-attack investigation

      - Proof of regulatory compliance

      - Data leakage prevention

   Many application service providers simply terminate sessions to/from
   the Internet at the edge of the data center in the form of SSL/TLS
   offload in the load balancer.  Not only does this reduce the load on
   application servers, it simplifies the processes to enable monitoring
   of the session content.

   However, in some situations, encryption deeper in the data center may
   be necessary to protect personal information or in order to meet
   industry regulations, e.g., those set out by the Payment Card
   Industry (PCI).  In such situations, various methods have been used
   to allow service assurance and security processes to access
   unencrypted data.  These include SSL/TLS decryption in dedicated
   units, which then forward packets to SP-controlled tools, or real-
   time or post-capture decryption in the tools themselves.  A number of
   these tools provide passive decryption by providing the monitoring
   device with the server's private key.  The move to increased use of
   the forward-secret key exchange mechanism impacts the use of these
   techniques.

   Operators of data centers may also maintain packet recordings in
   order to be able to investigate attacks, breaches of internal
   processes, etc.  In some industries, organizations may be legally
   required to maintain such information for compliance purposes.



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   Investigations of this nature have used access to the unencrypted
   contents of the packet.  Alternate methods to investigate attacks or
   breaches of process will rely on endpoint information, such as logs.
   As previously noted, logs often lack complete information, and this
   is seen as a concern resulting in some relying on session access for
   additional information.

   Application service providers may offer content-level monitoring
   options to detect intellectual property leakage or other attacks.  In
   service provider environments where Data Loss Prevention (DLP) has
   been implemented on the basis of the service provider having
   cleartext access to session streams, the use of encrypted streams
   prevents these implementations from conducting content searches for
   the keywords or phrases configured in the DLP system.  DLP is often
   used to prevent the leakage of Personally Identifiable Information
   (PII) as well as financial account information, Personal Health
   Information (PHI), and PCI.  If session encryption is terminated at a
   gateway prior to accessing these services, DLP on session data can
   still be performed.  The decision of where to terminate encryption to
   hosted environments will be a risk decision made between the
   application service provider and customer organization according to
   their priorities.  DLP can be performed at the server for the hosted
   application and on an end user's system in an organization as
   alternate or additional monitoring points of content; however, this
   is not frequently done in a service provider environment.

   Application service providers, by their very nature, control the
   application endpoint.  As such, much of the information gleaned from
   sessions is still available on that endpoint.  However, when a gap
   exists in the application's logging and debugging capabilities, it
   has led the application service provider to access data in transport
   for monitoring and debugging.

3.2.  Hosted Applications

   Organizations are increasingly using hosted applications rather than
   in-house solutions that require maintenance of equipment and
   software.  Examples include Enterprise Resource Planning (ERP)
   solutions, payroll service, time and attendance, travel and expense
   reporting, among others.  Organizations may require some level of
   management access to these hosted applications and will typically
   require session encryption or a dedicated channel for this activity.

   In other cases, hosted applications may be fully managed by a hosting
   service provider with SLA expectations for availability and
   performance as well as for security functions including malware
   detection.  Due to the sensitive nature of these hosted environments,
   the use of encryption is already prevalent.  Any impact may be



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   similar to an enterprise with tools being used inside of the hosted
   environment to monitor traffic.  Additional concerns were not
   reported in the call for contributions.

3.2.1.  Monitoring Managed Applications

   Performance, availability, and other aspects of an SLA are often
   collected through passive monitoring.  For example:

   o  Availability: ability to establish connections with hosts to
      access applications and to discern the difference between network-
      or host-related causes of unavailability.

   o  Performance: ability to complete transactions within a target
      response time and to discern the difference between network- or
      host-related causes of excess response time.

   Here, as with all passive monitoring, the accuracy of inferences is
   dependent on the cleartext information available, and encryption
   would tend to reduce the information and, therefore, the accuracy of
   each inference.  Passive measurement of some metrics will be
   impossible with encryption that prevents inferring-packet
   correspondence across multiple observation points, such as for
   packet-loss metrics.

   Application logging currently lacks detail sufficient to make
   accurate inferences in an environment with increased encryption, and
   so this constitutes a gap for passive performance monitoring (which
   could be closed if log details are enhanced in the future).

3.2.2.  Mail Service Providers

   Mail (application) service providers vary in what services they
   offer.  Options may include a fully hosted solution where mail is
   stored external to an organization's environment on mail service
   provider equipment or the service offering may be limited to monitor
   incoming mail to remove spam (Section 5.1), phishing attacks
   (Section 5.3), and malware (Section 5.6) before mail is directed to
   the organization's equipment.  In both of these cases, content of the
   messages and headers is monitored to detect and remove messages that
   are undesirable or that may be considered an attack.

   STARTTLS should have zero effect on anti-spam efforts for SMTP
   traffic.  Anti-spam services could easily be performed on an SMTP
   gateway, eliminating the need for TLS decryption services.  The
   impact to anti-spam service providers should be limited to a change
   in tools, where middleboxes were deployed to perform these functions.




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   Many efforts are emerging to improve user-to-user encryption,
   including promotion of PGP and newer efforts such as Dark Mail
   [DarkMail].  Of course, content-based spam filtering will not be
   possible on encrypted content.

3.3.  Data Storage

   Numerous service offerings exist that provide hosted storage
   solutions.  This section describes the various offerings and details
   the monitoring for each type of service and how encryption may impact
   the operational and security monitoring performed.

   Trends in data storage encryption for hosted environments include a
   range of options.  The following list is intentionally high-level to
   describe the types of encryption used in coordination with data
   storage that may be hosted remotely, meaning the storage is
   physically located in an external data center requiring transport
   over the Internet.  Options for monitoring will vary with each
   encryption approach described below.  In most cases, solutions have
   been identified to provide encryption while ensuring management
   capabilities were maintained through logging or other means.

3.3.1.  Object-Level Encryption

   For higher security and/or privacy of data and applications, options
   that provide end-to-end encryption of the data from the user's
   desktop or server to the storage platform may be preferred.  This
   description includes any solution that encrypts data at the object
   level, not the transport level.  Encryption of data may be performed
   with libraries on the system or at the application level, which
   includes file-encryption services via a file manager.  Object-level
   encryption is useful when data storage is hosted or scenarios when
   the storage location is determined based on capacity or based on a
   set of parameters to automate decisions.  This could mean that large
   datasets accessed infrequently could be sent to an off-site storage
   platform at an external hosting service, data accessed frequently may
   be stored locally, or the decision of where to store datasets could
   be based on the transaction type.  Object-level encryption is grouped
   separately for the purpose of this document since data may be stored
   in multiple locations including off-site remote storage platforms.
   If session encryption is also used, the protocol is likely to be TLS.

   Impacts to monitoring may include access to content inspection for
   data-leakage prevention and similar technologies, depending on their
   placement in the network.






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3.3.1.1.  Monitoring for Hosted Storage

   Monitoring of hosted storage solutions that use host-level (object)
   encryption is described in this subsection.  Host-level encryption
   can be employed for backup services and occasionally for external
   storage services (operated by a third party) when internal storage
   limits are exceeded.

   Monitoring of data flows to hosted storage solutions is performed for
   security and operational purposes.  The security monitoring may be to
   detect anomalies in the data flows that could include changes to
   destination, the amount of data transferred, or alterations in the
   size and frequency of flows.  Operational considerations include
   capacity and availability monitoring.

3.3.2.  Disk Encryption, Data at Rest (DAR)

   There are multiple ways to achieve full disk encryption for stored
   data.  Encryption may be performed on data to be stored while in
   transit close to the storage media with solutions like Controller
   Based Encryption (CBE) or in the drive system with Self-Encrypting
   Drives (SEDs).  Session encryption is typically coupled with
   encryption of these data at rest (DAR) solutions to also protect data
   in transit.  Transport encryption is likely via TLS.

3.3.2.1.  Monitoring Session Flows for DAR Solutions

   Monitoring for transport of data-to-storage platforms, where object-
   level encryption is performed close to or on the storage platform, is
   similar to that described in Section 3.3.1.1.  The primary difference
   for these solutions is the possible exposure of sensitive
   information, which could include privacy-related data, financial
   information, or intellectual property if session encryption via TLS
   is not deployed.  Session encryption is typically used with these
   solutions, but that decision would be based on a risk assessment.
   There are use cases where DAR or disk-level encryption is required.
   Examples include preventing exposure of data if physical disks are
   stolen or lost.  In the case where TLS is in use, monitoring and the
   exposure of data is limited to a 5-tuple.

3.3.3.  Cross-Data-Center Replication Services

   Storage services also include data replication, which may occur
   between data centers and may leverage Internet connections to tunnel
   traffic.  The traffic may use an Internet Small Computer System
   Interface (iSCSI) [RFC7143] or Fibre Channel over TCP/IP (FCIP)
   [RFC7146] encapsulated in IPsec.  Either transport or tunnel mode may
   be used for IPsec depending upon the termination points of the IPsec



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   session, if it is from the storage platform itself or from a gateway
   device at the edge of the data center, respectively.

3.3.3.1.  Monitoring IPsec for Data Replication Services

   The monitoring of data flows between data centers (for data
   replication) may be performed for security and operational purposes
   and would typically concentrate more on operational aspects since
   these flows are essentially virtual private networks (VPNs) between
   data centers.  Operational considerations include capacity and
   availability monitoring.  The security monitoring may be to detect
   anomalies in the data flows, similar to what was described in
   Section 3.3.1.1.  If IPsec tunnel mode is in use, monitoring is
   limited to a 2-tuple; with transport mode, it's limited to a 5-tuple.

4.  Encryption for Enterprises

   Encryption of network traffic within the private enterprise is a
   growing trend, particularly in industries with audit and regulatory
   requirements.  Some enterprise-internal networks are almost
   completely TLS and/or IPsec encrypted.

   For each type of monitoring, different techniques and access to parts
   of the data stream are part of current practice.  As we transition to
   an increased use of encryption, alternate methods of monitoring for
   operational purposes may be necessary to reduce the practice of
   breaking encryption (other policies may apply in some enterprise
   settings).

4.1.  Monitoring Practices of the Enterprise

   Large corporate enterprises are the owners of the platforms, data,
   and network infrastructure that provide critical business services to
   their user communities.  As such, these enterprises are responsible
   for all aspects of the performance, availability, security, and
   quality of experience for all user sessions.  In many such
   enterprises, users are required to consent to the enterprise
   monitoring all their activities as a condition of employment.
   Subsections of Section 4 discuss techniques that access data beyond
   the data-link, network, and transport-level headers typically used in
   service provider networks since the corporate enterprise owns the
   data.  These responsibilities break down into three basic areas:

   1.  Security Monitoring and Control

   2.  Application-Performance Monitoring and Reporting

   3.  Network Diagnostics and Troubleshooting



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   In each of the above areas, technical support teams utilize
   collection, monitoring, and diagnostic systems.  Some organizations
   currently use attack methods such as replicated TLS server RSA
   private keys to decrypt passively monitored copies of encrypted TLS
   packet streams.

   For an enterprise to avoid costly application down time and deliver
   expected levels of performance, protection, and availability, some
   forms of traffic analysis, sometimes including examination of packet
   payloads, are currently used.

4.1.1.  Security Monitoring in the Enterprise

   Enterprise users are subject to the policies of their organization
   and the jurisdictions in which the enterprise operates.  As such,
   proxies may be in use to:

   1.  intercept outbound session traffic to monitor for intellectual
       property leakage (by users, malware, and trojans),

   2.  detect viruses/malware entering the network via email or web
       traffic,

   3.  detect malware/trojans in action, possibly connecting to remote
       hosts,

   4.  detect attacks (cross-site scripting and other common web-related
       attacks),

   5.  track misuse and abuse by employees,

   6.  restrict the types of protocols permitted to/from the entire
       corporate environment, and

   7.  detect and defend against Internet DDoS attacks, including both
       volumetric and Layer 7 attacks.

   A significant portion of malware hides its activity within TLS or
   other encryption protocols.  This includes lateral movement, Command
   and Control (C&C), and Data Exfiltration.

   The impact to a fully encrypted internal network would include cost
   and possible loss of detection capabilities associated with the
   transformation of the network architecture and tools for monitoring.
   The capabilities of detection through traffic fingerprinting,
   logging, host-level transaction monitoring, and flow analysis would
   vary depending on access to a 2-tuple or 5-tuple in the network as
   well.



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   Security monitoring in the enterprise may also be performed at the
   endpoint with numerous current solutions that mitigate the same
   problems as some of the above-mentioned solutions.  Since the
   software agents operate on the device, they are able to monitor
   traffic before it is encrypted, monitor for behavior changes and lock
   down devices to use only the expected set of applications.  Session
   encryption does not affect these solutions.  Some might argue that
   scaling is an issue in the enterprise, but some large enterprises
   have used these tools effectively.

   Use of bring-your-own-device (BYOD) policies within organizations may
   limit the scope of monitoring permitted with these alternate
   solutions.  Network endpoint assessment (NEA) or the use of virtual
   hosts could help to bridge the monitoring gap.

4.1.2.  Monitoring Application Performance in the Enterprise

   There are two main goals of monitoring:

   1.  Assess traffic volume on a per-application basis for billing,
       capacity planning, optimization of geographical location for
       servers or proxies, and other goals.

   2.  Assess performance in terms of application response time and
       user-perceived response time.

   Network-based application-performance monitoring tracks application
   response time by user and by URL, which is the information that the
   application owners and the lines of business request.  CDNs add
   complexity in determining the ultimate endpoint destination.  By
   their very nature, such information is obscured by CDNs and encrypted
   protocols, adding a new challenge for troubleshooting network and
   application problems.  URL identification allows the application
   support team to do granular, code-level troubleshooting at multiple
   tiers of an application.

   New methodologies to monitor user-perceived response time and to
   separate network from server time are evolving.  For example, the
   IPv6 Destination Option Header (DOH) implementation of Performance
   and Diagnostic Metrics (PDM) [RFC8250] will provide this.  Using PDM
   with IPsec Encapsulating Security Payload (ESP) Transport Mode
   requires placement of the PDM DOH within the ESP-encrypted payload to
   avoid leaking timing and sequence number information that could be
   useful to an attacker.  Use of PDM DOH also may introduce some
   security weaknesses, including a timing attack, as described in
   Section 4 of [RFC8250].  For these and other reasons, [RFC8250]





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   requires that the PDM DOH option be explicitly turned on by
   administrative action in each host where this measurement feature
   will be used.

4.1.3.  Diagnostics and Troubleshooting for Enterprise Networks

   One primary key to network troubleshooting is the ability to follow a
   transaction through the various tiers of an application in order to
   isolate the fault domain.  A variety of factors relating to the
   structure of the modern data center and multi-tiered application have
   made it difficult to follow a transaction in network traces without
   the ability to examine some of the packet payload.  Alternate
   methods, such as log analysis, need improvement to fill this gap.

4.1.3.1.  Address Sharing (NAT)

   CDNs, NATs, and Network Address and Port Translators (NAPTs) obscure
   the ultimate endpoint designation (see [RFC6269] for types of address
   sharing and a list of issues).  Troubleshooting a problem for a
   specific end user requires finding information such as the IP address
   and other identifying information so that their problem can be
   resolved in a timely manner.

   NAT is also frequently used by lower layers of the data-center
   infrastructure.  Firewalls, load balancers, web servers, app servers,
   and middleware servers all regularly NAT the source IP of packets.
   Combine this with the fact that users are often allocated randomly by
   load balancers to all these devices, and the network troubleshooter
   is often left with very few options in today's environment due to
   poor logging implementations in applications.  As such, network
   troubleshooting is used to trace packets at a particular layer,
   decrypt them, and look at the payload to find a user session.

   This kind of bulk packet capture and bulk decryption is frequently
   used when troubleshooting a large and complex application.  Endpoints
   typically don't have the capacity to handle this level of network
   packet capture, so out-of-band networks of robust packet brokers and
   network sniffers that use techniques such as copies of TLS RSA
   private keys accomplish this task today.

4.1.3.2.  TCP Pipelining / Session Multiplexing

   TCP pipelining / session multiplexing used mainly by middleboxes
   today allows for multiple end-user sessions to share the same TCP
   connection.  This raises several points of interest with an increased
   use of encryption.  TCP session multiplexing should still be possible
   when TLS or TCPcrypt is in use since the TCP header information is
   exposed, leaving the 5-tuple accessible.  The use of TCP session



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   multiplexing of an IP-layer encryption, e.g., IPsec, that only
   exposes a 2-tuple would not be possible.  Troubleshooting
   capabilities with encrypted sessions from the middlebox may limit
   troubleshooting to the use of logs from the endpoints performing the
   TCP multiplexing or from the middleboxes prior to any additional
   encryption that may be added to tunnel the TCP multiplexed traffic.

   Increased use of HTTP/2 will likely further increase the prevalence
   of session multiplexing, both on the Internet and in the private data
   center.  HTTP pipelining requires both the client and server to
   participate; visibility of packets once encrypted will hide the use
   of HTTP pipelining for any monitoring that takes place outside of the
   endpoint or proxy solution.  Since HTTP pipelining is between a
   client and server, logging capabilities may require improvement in
   some servers and clients for debugging purposes if this is not
   already possible.  Visibility for middleboxes includes anything
   exposed by TLS and the 5-tuple.

4.1.3.3.  HTTP Service Calls

   When an application server makes an HTTP service call to back-end
   services on behalf of a user session, it uses a completely different
   URL and a completely different TCP connection.  Troubleshooting via
   network trace involves matching up the user request with the HTTP
   service call.  Some organizations do this today by decrypting the TLS
   packet and inspecting the payload.  Logging has not been adequate for
   their purposes.

4.1.3.4.  Application-Layer Data

   Many applications use text formats such as XML to transport data or
   application-level information.  When transaction failures occur and
   the logs are inadequate to determine the cause, network and
   application teams work together, each having a different view of the
   transaction failure.  Using this troubleshooting method, the network
   packet is correlated with the actual problem experienced by an
   application to find a root cause.  The inability to access the
   payload prevents this method of troubleshooting.

4.2.  Techniques for Monitoring Internet-Session Traffic

   Corporate networks commonly monitor outbound session traffic to
   detect or prevent attacks as well as to guarantee service-level
   expectations.  In some cases, alternate options are available when
   encryption is in use through a proxy or a shift to monitoring at the
   endpoint.  In both cases, scaling is a concern, and advancements to
   support this shift in monitoring practices will assist the deployment
   of end-to-end encryption.



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   Some DLP tools intercept traffic at the Internet gateway or proxy
   services with the ability to MITM encrypted session traffic (HTTP/
   TLS).  These tools may monitor for key words important to the
   enterprise including business-sensitive information such as trade
   secrets, financial data, PII, or PHI.  Various techniques are used to
   intercept HTTP/TLS sessions for DLP and other purposes and can be
   misused as described in "Summarizing Known Attacks on Transport Layer
   Security (TLS) and Datagram TLS (DTLS)" [RFC7457] (see Section 2.8).
   Note: many corporate policies allow access to personal financial and
   other sites for users without interception.  Another option is to
   terminate a TLS session prior to the point where monitoring is
   performed.  Aside from exposing user information to the enterprise,
   MITM devices often are subject to severe security defects, which can
   lead to exposure of user data to attackers outside the enterprise
   user data [UserData].  In addition, implementation errors in
   middleboxes have led to major difficulties in deploying new versions
   of security protocols such as TLS [Ben17a] [Ben17b] [Res17a]
   [Res17b].

   Monitoring traffic patterns for anomalous behavior such as increased
   flows of traffic that could be bursty at odd times or flows to
   unusual destinations (small or large amounts of traffic) is common.
   This traffic may or may not be encrypted, and various methods of
   encryption or just obfuscation may be used.

   Web-filtering devices are sometimes used to allow only access to
   well-known sites found to be legitimate and free of malware on last
   check by a web-filtering service company.  One common example of web
   filtering in a corporate environment is blocking access to sites that
   are not well known to these tools for the purpose of blocking
   malware; this may be noticeable to those in research who are unable
   to access colleagues' individual sites or new websites that have not
   yet been screened.  In situations where new sites are required for
   access, they can typically be added after notification by the user or
   log alerts and review.  Account access for personal mail may be
   blocked in corporate settings to prevent another vector for malware
   from entering as well as to prevent intellectual property leaks out
   of the network.  This method remains functional with increased use of
   encryption and may be more effective at preventing malware from
   entering the network.  Some enterprises may be more aggressive in
   their filtering and monitoring policy, causing undesirable outcomes.
   Web-filtering solutions monitor and potentially restrict access based
   on the destination URL (when available), server name, IP address, or
   DNS name.  A complete URL may be used in cases where access
   restrictions vary for content on a particular site or for the sites
   hosted on a particular server.  In some cases, the enterprise may use
   a proxy to access this additional information based on their policy.
   This type of restriction is intended to be transparent to users in a



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   corporate setting as the typical corporate user does not access sites
   that are not well known to these tools.  However, the mechanisms that
   these web filters use to do monitoring and enforcement have the
   potential to cause access issues or other user-visible failures.

   Desktop DLP tools are used in some corporate environments as well.
   Since these tools reside on the desktop, they can intercept traffic
   before it is encrypted and may provide a continued method for
   monitoring leakage of intellectual property from the desktop to the
   Internet or attached devices.

   DLP tools can also be deployed by network service providers, as they
   have the vantage point of monitoring all traffic paired with
   destinations off the enterprise network.  This makes an effective
   solution for enterprises that allow "bring-your-own" devices when the
   traffic is not encrypted and for devices outside the desktop category
   (such as mobile phones) that are used on corporate networks
   nonetheless.

   Enterprises may wish to reduce the traffic on their Internet access
   facilities by monitoring requests for within-policy content and
   caching it.  In this case, repeated requests for Internet content
   spawned by URLs in email trade newsletters or other sources can be
   served within the enterprise network.  Gradual deployment of end-to-
   end encryption would tend to reduce the cacheable content over time,
   owing to concealment of critical headers and payloads.  Many forms of
   enterprise-performance management may be similarly affected.  It
   should be noted that transparent caching is considered an anti-
   pattern.

5.  Security Monitoring for Specific Attack Types

   Effective incident response today requires collaboration at Internet
   scale.  This section will only focus on efforts of collaboration at
   Internet scale that are dedicated to specific attack types.  They may
   require new monitoring and detection techniques in an increasingly
   encrypted Internet.  As mentioned previously, some service providers
   have been interfering with STARTTLS to prevent session encryption to
   be able to perform functions they are used to (injecting ads,
   monitoring, etc.).  By detailing the current monitoring methods used
   for attack detection and response, this information can be used to
   devise new monitoring methods that will be effective in the changed
   Internet via collaboration and innovation.

   Changes to improve encryption or to deploy OS methods have little
   impact on the detection of malicious actors.  Malicious actors have
   had access to strong encryption for quite some time.  Incident
   responders, in many cases, have developed techniques to locate



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   malicious traffic within encrypted sessions.  The following section
   will note some examples where detection and mitigation of such
   traffic has been successful.

5.1.  Mail Abuse and Spam

   The largest operational effort to prevent mail abuse is through the
   Messaging, Malware, Mobile Anti-Abuse Working Group (M3AAWG)
   [M3AAWG].  Mail abuse is combatted directly with mail administrators
   who can shut down or stop continued mail abuse originating from
   large-scale providers that participate in using the Abuse Reporting
   Format (ARF) agents standardized in the IETF [RFC5965] [RFC6430]
   [RFC6590] [RFC6591] [RFC6650] [RFC6651] [RFC6652].  The ARF agent
   directly reports abuse messages to the appropriate service provider
   who can take action to stop or mitigate the abuse.  Since this
   technique uses the actual message, the use of SMTP over TLS between
   mail gateways will not affect its usefulness.  As mentioned
   previously, SMTP over TLS only protects data while in transit, and
   the messages may be exposed on mail servers or mail gateways if a
   user-to-user encryption method is not used.  Current user-to-user
   message encryption methods on email (S/MIME and PGP) do not encrypt
   the email header information used by ARF and the service provider
   operators in their efforts to mitigate abuse.

   Another effort, "Domain-based Message Authentication, Reporting, and
   Conformance (DMARC)" [RFC7489], is a mechanism for policy
   distribution that enables increasingly strict handling of messages
   that fail authentication checks, ranging from no action, through
   altered delivery, up to message rejection.  DMARC is also not
   affected by the use of STARTTLS.

5.2.  Denial of Service

   Responses to Denial-of-Service (DoS) attacks are typically
   coordinated by the service provider community with a few key vendors
   who have tools to assist in the mitigation efforts.  Traffic patterns
   are determined from each DoS attack to stop or rate limit the traffic
   flows with patterns unique to that DoS attack.

   Data types used in monitoring traffic for DDoS are described in the
   documents in development by the DDoS Open Threat Signaling (DOTS)
   [DOTS] Working Group.  The impact of encryption can be understood
   from their documented use cases [DDOS-USECASE].

   Data types used in DDoS attacks have been detailed in the Incident
   Object Description Exchange Format (IODEF) Guidance document (see
   [RFC8274], Appendix B.2) with the help of several members of the
   service provider community.  The examples provided are intended to



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   help identify the useful data in detecting and mitigating these
   attacks independent of the transport and protocol descriptions in the
   documents.

5.3.  Phishing

   Investigations and responses to phishing attacks follow well-known
   patterns, requiring access to specific fields in email headers as
   well as content from the body of the message.  When reporting
   phishing attacks, the recipient has access to each field as well as
   the body to make content reporting possible, even when end-to-end
   encryption is used.  The email header information is useful to
   identify the mail servers and accounts used to generate or relay the
   attack messages in order to take the appropriate actions.  The
   content of the message often includes an embedded attack that may be
   in an infected file or may be a link that results in the download of
   malware to the user's system.

   Administrators often find it helpful to use header information to
   track down similar messages in their mail queue or in users' inboxes
   to prevent further infection.  Combinations of To:, From:, Subject:,
   and Received: from header information might be used for this purpose.
   Administrators may also search for document attachments of the same
   name or size or that contain a file with a matching hash to a known
   phishing attack.  Administrators might also add URLs contained in
   messages to block lists locally, or this may also be done by browser
   vendors through larger-scale efforts like that of the Anti-Phishing
   Working Group (APWG).  See "Coordinating Attack Response at Internet
   Scale (CARIS) Workshop Report" [RFC8073] for additional information
   and pointers to the APWG's efforts on anti-phishing.

   A full list of the fields used in phishing attack incident responses
   can be found in RFC 5901.  Future plans to increase privacy
   protections may limit some of these capabilities if some email header
   fields are encrypted, such as the To:, From:, and Subject: header
   fields.  This does not mean that those fields should not be
   encrypted, only that we should be aware of how they are currently
   used.

   Some products protect users from phishing by maintaining lists of
   known phishing domains (such as misspelled bank names) and blocking
   access.  This can be done by observing DNS, cleartext HTTP, or Server
   Name Indication (SNI) in TLS, in addition to analyzing email.
   Alternate options to detect and prevent phishing attacks may be
   needed.  More recent examples of data exchanged in spear phishing
   attacks has been detailed in the IODEF Guidance document (see
   [RFC8274], Appendix B.3).




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5.4.  Botnets

   Botnet detection and mitigation is complex as botnets may involve
   hundreds or thousands of hosts with numerous C&C servers.  The
   techniques and data used to monitor and detect each may vary.
   Connections to C&C servers are typically encrypted; therefore, a move
   to an increasingly encrypted Internet may not affect the detection
   and sharing methods used.

5.5.  Malware

   Techniques for the detection and monitoring of malware vary.  As
   mentioned in Section 4, malware monitoring may occur at gateways to
   the organization analyzing email and web traffic.  These services can
   also be provided by service providers, changing the scale and
   location of this type of monitoring.  Additionally, incident
   responders may identify attributes unique to types of malware to help
   track down instances by their communication patterns on the Internet
   or by alterations to hosts and servers.

   Data types used in malware investigations have been summarized in an
   example of the IODEF Guidance document (see [RFC8274], Appendix B.3).

5.6.  Spoofed-Source IP Address Protection

   The IETF has reacted to spoofed-source IP address-based attacks,
   recommending the use of network ingress filtering in BCP 38 [RFC2827]
   and of the unicast Reverse Path Forwarding (uRPF) mechanism
   [RFC3704].  But uRPF suffers from limitations regarding its
   granularity: a malicious node can still use a spoofed IP address
   included inside the prefix assigned to its link.  Source Address
   Validation Improvement (SAVI) mechanisms try to solve this issue.
   Basically, a SAVI mechanism is based on the monitoring of a specific
   address assignment/management protocol (e.g., Stateless Address
   Autoconfiguration (SLAAC) [RFC4862], Secure Neighbor Discovery (SEND)
   [RFC3971], and DHCPv4/v6 [RFC2131][RFC3315]) and, according to this
   monitoring, sets up a filtering policy allowing only the IP flows
   with a correct source IP address (i.e., any packet with a source IP
   address from a node not owning it is dropped).  The encryption of
   parts of the address assignment/management protocols, critical for
   SAVI mechanisms, can result in a dysfunction of the SAVI mechanisms.

5.7.  Further Work

   Although incident response work will continue, new methods to prevent
   system compromise through security automation and continuous
   monitoring [SACM] may provide alternate approaches where system
   security is maintained as a preventative measure.



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6.  Application-Based Flow Information Visible to a Network

   This section describes specific techniques used in monitoring
   applications that are visible to the network if a 5-tuple is exposed
   and as such can potentially be used as input for future network-
   management approaches.  It also includes an overview of IP Flow
   Information Export (IPFIX), a flow-based protocol used to export
   information about network flows.

6.1.  IP Flow Information Export

   Many of the accounting, monitoring, and measurement tasks described
   in this document, especially in Sections 2.3.2, 3.1.1, 4.1.3, 4.2,
   and 5.2, use the IPFIX protocol [RFC7011] for export and storage of
   the monitored information.  IPFIX evolved from the widely deployed
   NetFlow protocol [RFC3954], which exports information about flows
   identified by 5-tuple.  While NetFlow was largely concerned with
   exporting per-flow byte and packet counts for accounting purposes,
   IPFIX's extensible Information Model [RFC7012] provides a variety of
   Information Elements (IEs) [IPFIX-IANA] for representing information
   above and below the traditional network-layer flow information.
   Enterprise-specific IEs allow exporter vendors to define their own
   non-standard IEs as well, and many of these are driven by header and
   payload inspection at the Metering Process.

   While the deployment of encryption has no direct effect on the use of
   IPFIX, certain defined IEs may become unavailable when the Metering
   Process observing the traffic cannot decrypt former cleartext
   information.  For example, HTTPS renders HTTP header analysis
   impossible, so IEs derived from the header (e.g., httpContentType,
   httpUserAgent) cannot be exported.

   The collection of IPFIX data itself, of course, provides a point of
   centralization for information that is potentially business and
   privacy critical.  The IPFIX File Format specification [RFC5655]
   recommends encryption for this data at rest, and the IP Flow
   Anonymization specification [RFC6235] defines a metadata format for
   describing the anonymization functions applied to an IPFIX dataset,
   if anonymization is employed for data sharing of IPFIX information
   between enterprises or network operators.

6.2.  TLS Server Name Indication

   When initiating the TLS handshake, the client may provide an
   extension field (server_name) that indicates the server to which it
   is attempting a secure connection.  TLS SNI was standardized in 2003
   to enable servers to present the "correct TLS certificate" to clients
   in a deployment of multiple virtual servers hosted by the same server



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   infrastructure and IP address.  Although this is an optional
   extension, it is today supported by all modern browsers, web servers,
   and developer libraries.  Akamai [Nygren] reports that many of their
   customers see client TLS SNI usage over 99%.  It should be noted that
   HTTP/2 introduces the Alt-SVC method for upgrading the connection
   from HTTP/1 to either unencrypted or encrypted HTTP/2.  If the
   initial HTTP/1 request is unencrypted, the destination alternate
   service name can be identified before the communication is
   potentially upgraded to encrypted HTTP/2 transport.  HTTP/2 requires
   the TLS implementation to support the SNI extension (see Section 9.2
   of [RFC7540]).  It is also worth noting that [RFC7838] "allows an
   origin server to nominate additional means of interacting with it on
   the network", while [RFC8164] allows for a URI to be accessed with
   HTTP/2 and TLS using Opportunistic Security (on an experimental
   basis).

   This information is only available if the client populates the SNI
   extension.  Doing so is an optional part of the TLS standard, and as
   stated above, this has been implemented by all major browsers.  Due
   to its optional nature, though, existing network filters that examine
   a TLS ClientHello for an SNI extension cannot expect to always find
   one.  "SNI Encryption in TLS Through Tunneling" [SNI-TLS] has been
   adopted by the TLS Working Group, which provides solutions to encrypt
   SNI.  As such, there will be an option to encrypt SNI in future
   versions of TLS.  The per-domain nature of SNI may not reveal the
   specific service or media type being accessed, especially where the
   domain is of a provider offering a range of email, video, web pages,
   etc.  For example, certain blog or social network feeds may be deemed
   "adult content", but the SNI will only indicate the server domain
   rather than a URL path.

   There are additional issues for identification of content using SNI:
   [RFC7540] includes connection coalescing, [RFC8336] defines the
   ORIGIN frame, and the proposal outlined in [HTTP2-CERTS] will
   increase the difficulty of passive monitoring.

6.3.  Application-Layer Protocol Negotiation (ALPN)

   ALPN is a TLS extension that may be used to indicate the application
   protocol within the TLS session.  This is likely to be of more value
   to the network where it indicates a protocol dedicated to a
   particular traffic type (such as video streaming) rather than a
   multi-use protocol.  ALPN is used as part of HTTP/2 'h2', but will
   not indicate the traffic types that may make up streams within an
   HTTP/2 multiplex.  ALPN is sent cleartext in the ClientHello, and the
   server returns it in Encrypted Extensions in TLS 1.3.





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6.4.  Content Length, Bitrate, and Pacing

   The content length of encrypted traffic is effectively the same as
   that of the cleartext.  Although block ciphers utilize padding, this
   makes a negligible difference.  Bitrate and pacing are generally
   application specific and do not change much when the content is
   encrypted.  Multiplexed formats (such as HTTP/2 and QUIC [QUIC]) may,
   however, incorporate several application streams over one connection,
   which makes the bitrate/pacing no longer application specific.  Also,
   packet padding is available in HTTP/2, TLS 1.3, and many other
   protocols.  Traffic analysis is made more difficult by such
   countermeasures.

7.  Effect of Encryption on the Evolution of Mobile Networks

   Transport header encryption prevents the use of transit proxies in
   the center of the network and the use of some edge proxies by
   preventing the proxies from taking action on the stream.  It may be
   that the claimed benefits of such proxies could be achieved by
   end-to-end client and server optimizations, distribution using CDNs,
   plus the ability to continue connections across different access
   technologies (across dynamic user IP addresses).  The following
   aspects should be considered in this approach:

   1.  In a wireless mobile network, the delay and channel capacity per
       user and sector varies due to coverage, contention, user
       mobility, scheduling balances fairness, capacity, and service
       QoE.  If most users are at the cell edge, the controller cannot
       use more-complex Quadrature Amplitude Modulation (QAM), thus
       reducing total cell capacity; similarly, if a Universal Mobile
       Telecommunications System (UMTS) edge is serving some number of
       CS-Voice Calls, the remaining capacity for packet services is
       reduced.

   2.  Mobile wireless networks service inbound roamers (users of
       Operator A in the foreign network of Operator B) by backhauling
       their traffic through the network (from Operator B to Operator A)
       and then serving them through the P-Gateway (PGW), General Packet
       Radio Service (GPRS) Support Node (GGSN), CDN, etc., of Operator
       A (the user's home operator).  Increasing window sizes to
       compensate for the path RTT will have the limitations outlined
       earlier for TCP.  The outbound roamer scenario has a similar TCP
       performance impact.

   3.  Issues in deploying CDNs in Radio Access Networks (RANs) include
       decreasing the client-server control loop that requires deploying
       CDNs / Cloud functions that terminate encryption closer to the
       edge.  In Cellular RAN, the user IP traffic is encapsulated into



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       GPRS Tunneling Protocol-User Plane (GTP-U in UMTS and LTE)
       tunnels to handle user mobility; the tunnels terminate in
       APN/GGSN/PGW that are in central locations.  One user's traffic
       may flow through one or more APN's (for example, Internet APN,
       Roaming APN for Operator X, Video-Service APN, OnDeckAPN, etc.).
       The scope of operator private IP addresses may be limited to
       specific APNs.  Since CDNs generally operate on user IP flows,
       deploying them would require enhancing them with tunnel
       translation, tunnel-management functions, etc.

   4.  While CDNs that decrypt flows or split connection proxies
       (similar to split TCP) could be deployed closer to the edges to
       reduce control-loop RTT, with transport header encryption, such
       CDNs perform optimization functions only for partner client
       flows.  Therefore, content from some Small-Medium Businesses
       (SMBs) would not get such CDN benefits.

8.  Response to Increased Encryption and Looking Forward

   As stated in [RFC7258], "an appropriate balance [between network
   management and pervasive monitoring mitigations] will emerge over
   time as real instances of this tension are considered."  Numerous
   operators made it clear in their response to this document that they
   fully support strong encryption and providing privacy for end users;
   this is a common goal.  Operators recognize that not all the
   practices documented need to be supported going forward, either
   because of the risk to end-user privacy or because alternate
   technologies and tools have already emerged.  This document is
   intended to support network engineers and other innovators to work
   toward solving network and security management problems with protocol
   designers and application developers in new ways that facilitate
   adoption of strong encryption rather than preventing the use of
   encryption.  By having the discussions on network and security
   management practices with application developers and protocol
   designers, each side of the debate can understand each other's goals,
   work toward alternate solutions, and disband with practices that
   should no longer be supported.  A goal of this document is to assist
   the IETF in understanding some of the current practices so as to
   identify new work items for IETF-related use cases that can
   facilitate the adoption of strong session encryption and support
   network and security management.

9.  Security Considerations

   There are no additional security considerations as this is a summary
   and does not include a new protocol or functionality.





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10.  IANA Considerations

   This document has no IANA actions.

11.  Informative References

   [ACCORD]   IETF, "Alternatives to Content Classification for Operator
              Resource Deployment (accord) (BOF)", IETF-95 Proceedings,
              April 2016,
              <https://www.ietf.org/proceedings/95/accord.html>.

   [Ben17a]   Benjamin, D., "Chrome Data", Presentation before the TLS
              WG at IETF 100, November 2017,
              <https://datatracker.ietf.org/meeting/100/materials/
              slides-100-tls-sessa-tls13/>.

   [Ben17b]   Benjamin, D., "Subject: Additional TLS 1.3 results from
              Chrome", message to the TLS mailing list, 18 December
              2017, <https://www.ietf.org/mail-archive/web/tls/current/
              msg25168.html>.

   [CAIDA]    CAIDA, "The CAIDA USCD Anonymized Internet Traces 2016
              Dataset", <http://www.caida.org/data/passive/
              passive_2016_dataset.xml>.

   [DarkMail] "Dark Mail Technical Alliance", <https://darkmail.info/>.

   [DDOS-USECASE]
              Dobbins, R., Migault, D., Fouant, S., Moskowitz, R.,
              Teague, N., Xia, L., and K. Nishizuka, "Use cases for DDoS
              Open Threat Signaling", Work in Progress, draft-ietf-dots-
              use-cases-16, July 2018.

   [DOTS]     IETF, "DDoS Open Threat Signaling (dots)",
              <https://datatracker.ietf.org/wg/dots/charter>.

   [EFF2014]  Hoffman-Andrews, J., "ISPs Removing Their Customers' Email
              Encryption", November 2014,
              <https://www.eff.org/deeplinks/2014/11/
              starttls-downgrade-attacks>.

   [Enrich]   Narseo Vallina-Rodriguez, N., Sundaresan, S., Kreibich,
              C., and V. Paxson, "Header Enrichment or ISP Enrichment:
              Emerging Privacy Threats in Mobile Networks", Proceedings
              of the ACM SIGCOMM Workshop on Hot Topics in Middleboxes
              and Network Function Virtualization, pp. 23-30,
              DOI 10.1145/2785989.2786002, August 2015.




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   [GENEVE-REQS]
              Migault, D., Boutros, S., Wing, D., and S. Krishnan,
              "Geneve Protocol Security Requirements", Work in
              Progress, draft-mglt-nvo3-geneve-security-requirements-03,
              February 2018.

   [HTTP2-CERTS]
              Bishop, M., Sullivan, N., and M. Thomson, "Secondary
              Certificate Authentication in HTTP/2", Work in Progress,
              draft-ietf-httpbis-http2-secondary-certs-02, June 2018.

   [IPFIX-IANA]
              IANA, "IP Flow Information Export (IPFIX) Entities",
              <https://www.iana.org/assignments/ipfix/>.

   [JNSLP]    Eskens, S., "10 Standards for Oversight and Transparency
              of National Intelligence Services", Surveillance, Vol. 8,
              No. 3, July 2016, <http://jnslp.com/?s=10+Standards+for+Ov
              ersight+and+Transparency+of+National>.

   [M3AAWG]   M3AAWG, "Messaging, Malware and Mobile Anti-Abuse Working
              Group (M3AAWG)", <https://www.maawg.org/>.

   [MIDDLEBOXES]
              Dolson, D., Snellman, J., Boucadair, M., and C. Jacquenet,
              "An Inventory of Transport-centric Functions Provided by
              Middleboxes", Work in Progress, draft-dolson-transport-
              middlebox-03, June 2018.

   [Nygren]   Nygren, E., "Reaching toward Universal TLS SNI",
              Akamai Technologies, March 2017,
              <https://blogs.akamai.com/2017/03/
              reaching-toward-universal-tls-sni.html>.

   [QUIC]     IETF, "QUIC (quic)",
              <https://datatracker.ietf.org/wg/quic/charter/>.

   [Res17a]   Rescorla, E., "Subject: Preliminary data on Firefox TLS
              1.3 Middlebox experiment", message to the TLS mailing
              list, 5 December 2017, <https://www.ietf.org/mail-archive/
              web/tls/current/msg25091.html>.

   [Res17b]   Rescorla, E., "Subject: More compatibility measurement
              results", message to the TLS mailing list, 22 December
              2017, <https://www.ietf.org/mail-archive/web/tls/current/
              msg25179.html>.





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   [RFC1945]  Berners-Lee, T., Fielding, R., and H. Frystyk, "Hypertext
              Transfer Protocol -- HTTP/1.0", RFC 1945,
              DOI 10.17487/RFC1945, May 1996,
              <https://www.rfc-editor.org/info/rfc1945>.

   [RFC1958]  Carpenter, B., Ed., "Architectural Principles of the
              Internet", RFC 1958, DOI 10.17487/RFC1958, June 1996,
              <https://www.rfc-editor.org/info/rfc1958>.

   [RFC1984]  IAB and IESG, "IAB and IESG Statement on Cryptographic
              Technology and the Internet", BCP 200, RFC 1984,
              DOI 10.17487/RFC1984, August 1996,
              <https://www.rfc-editor.org/info/rfc1984>.

   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,
              <https://www.rfc-editor.org/info/rfc2131>.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <https://www.rfc-editor.org/info/rfc2474>.

   [RFC2663]  Srisuresh, P. and M. Holdrege, "IP Network Address
              Translator (NAT) Terminology and Considerations",
              RFC 2663, DOI 10.17487/RFC2663, August 1999,
              <https://www.rfc-editor.org/info/rfc2663>.

   [RFC2775]  Carpenter, B., "Internet Transparency", RFC 2775,
              DOI 10.17487/RFC2775, February 2000,
              <https://www.rfc-editor.org/info/rfc2775>.

   [RFC2804]  IAB and IESG, "IETF Policy on Wiretapping", RFC 2804,
              DOI 10.17487/RFC2804, May 2000,
              <https://www.rfc-editor.org/info/rfc2804>.

   [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
              May 2000, <https://www.rfc-editor.org/info/rfc2827>.

   [RFC3135]  Border, J., Kojo, M., Griner, J., Montenegro, G., and Z.
              Shelby, "Performance Enhancing Proxies Intended to
              Mitigate Link-Related Degradations", RFC 3135,
              DOI 10.17487/RFC3135, June 2001,
              <https://www.rfc-editor.org/info/rfc3135>.




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   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <https://www.rfc-editor.org/info/rfc3315>.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <https://www.rfc-editor.org/info/rfc3550>.

   [RFC3704]  Baker, F. and P. Savola, "Ingress Filtering for Multihomed
              Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March
              2004, <https://www.rfc-editor.org/info/rfc3704>.

   [RFC3724]  Kempf, J., Ed., Austein, R., Ed., and IAB, "The Rise of
              the Middle and the Future of End-to-End: Reflections on
              the Evolution of the Internet Architecture", RFC 3724,
              DOI 10.17487/RFC3724, March 2004,
              <https://www.rfc-editor.org/info/rfc3724>.

   [RFC3954]  Claise, B., Ed., "Cisco Systems NetFlow Services Export
              Version 9", RFC 3954, DOI 10.17487/RFC3954, October 2004,
              <https://www.rfc-editor.org/info/rfc3954>.

   [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
              "SEcure Neighbor Discovery (SEND)", RFC 3971,
              DOI 10.17487/RFC3971, March 2005,
              <https://www.rfc-editor.org/info/rfc3971>.

   [RFC4787]  Audet, F., Ed. and C. Jennings, "Network Address
              Translation (NAT) Behavioral Requirements for Unicast
              UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
              2007, <https://www.rfc-editor.org/info/rfc4787>.

   [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
              Address Autoconfiguration", RFC 4862,
              DOI 10.17487/RFC4862, September 2007,
              <https://www.rfc-editor.org/info/rfc4862>.

   [RFC5655]  Trammell, B., Boschi, E., Mark, L., Zseby, T., and A.
              Wagner, "Specification of the IP Flow Information Export
              (IPFIX) File Format", RFC 5655, DOI 10.17487/RFC5655,
              October 2009, <https://www.rfc-editor.org/info/rfc5655>.

   [RFC5965]  Shafranovich, Y., Levine, J., and M. Kucherawy, "An
              Extensible Format for Email Feedback Reports", RFC 5965,
              DOI 10.17487/RFC5965, August 2010,
              <https://www.rfc-editor.org/info/rfc5965>.



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   [RFC6108]  Chung, C., Kasyanov, A., Livingood, J., Mody, N., and B.
              Van Lieu, "Comcast's Web Notification System Design",
              RFC 6108, DOI 10.17487/RFC6108, February 2011,
              <https://www.rfc-editor.org/info/rfc6108>.

   [RFC6235]  Boschi, E. and B. Trammell, "IP Flow Anonymization
              Support", RFC 6235, DOI 10.17487/RFC6235, May 2011,
              <https://www.rfc-editor.org/info/rfc6235>.

   [RFC6269]  Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
              P. Roberts, "Issues with IP Address Sharing", RFC 6269,
              DOI 10.17487/RFC6269, June 2011,
              <https://www.rfc-editor.org/info/rfc6269>.

   [RFC6430]  Li, K. and B. Leiba, "Email Feedback Report Type Value:
              not-spam", RFC 6430, DOI 10.17487/RFC6430, November 2011,
              <https://www.rfc-editor.org/info/rfc6430>.

   [RFC6455]  Fette, I. and A. Melnikov, "The WebSocket Protocol",
              RFC 6455, DOI 10.17487/RFC6455, December 2011,
              <https://www.rfc-editor.org/info/rfc6455>.

   [RFC6590]  Falk, J., Ed. and M. Kucherawy, Ed., "Redaction of
              Potentially Sensitive Data from Mail Abuse Reports",
              RFC 6590, DOI 10.17487/RFC6590, April 2012,
              <https://www.rfc-editor.org/info/rfc6590>.

   [RFC6591]  Fontana, H., "Authentication Failure Reporting Using the
              Abuse Reporting Format", RFC 6591, DOI 10.17487/RFC6591,
              April 2012, <https://www.rfc-editor.org/info/rfc6591>.

   [RFC6650]  Falk, J. and M. Kucherawy, Ed., "Creation and Use of Email
              Feedback Reports: An Applicability Statement for the Abuse
              Reporting Format (ARF)", RFC 6650, DOI 10.17487/RFC6650,
              June 2012, <https://www.rfc-editor.org/info/rfc6650>.

   [RFC6651]  Kucherawy, M., "Extensions to DomainKeys Identified Mail
              (DKIM) for Failure Reporting", RFC 6651,
              DOI 10.17487/RFC6651, June 2012,
              <https://www.rfc-editor.org/info/rfc6651>.

   [RFC6652]  Kitterman, S., "Sender Policy Framework (SPF)
              Authentication Failure Reporting Using the Abuse Reporting
              Format", RFC 6652, DOI 10.17487/RFC6652, June 2012,
              <https://www.rfc-editor.org/info/rfc6652>.






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   [RFC7011]  Claise, B., Ed., Trammell, B., Ed., and P. Aitken,
              "Specification of the IP Flow Information Export (IPFIX)
              Protocol for the Exchange of Flow Information", STD 77,
              RFC 7011, DOI 10.17487/RFC7011, September 2013,
              <https://www.rfc-editor.org/info/rfc7011>.

   [RFC7012]  Claise, B., Ed. and B. Trammell, Ed., "Information Model
              for IP Flow Information Export (IPFIX)", RFC 7012,
              DOI 10.17487/RFC7012, September 2013,
              <https://www.rfc-editor.org/info/rfc7012>.

   [RFC7143]  Chadalapaka, M., Satran, J., Meth, K., and D. Black,
              "Internet Small Computer System Interface (iSCSI) Protocol
              (Consolidated)", RFC 7143, DOI 10.17487/RFC7143, April
              2014, <https://www.rfc-editor.org/info/rfc7143>.

   [RFC7146]  Black, D. and P. Koning, "Securing Block Storage Protocols
              over IP: RFC 3723 Requirements Update for IPsec v3",
              RFC 7146, DOI 10.17487/RFC7146, April 2014,
              <https://www.rfc-editor.org/info/rfc7146>.

   [RFC7230]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Message Syntax and Routing",
              RFC 7230, DOI 10.17487/RFC7230, June 2014,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC7234]  Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
              Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
              RFC 7234, DOI 10.17487/RFC7234, June 2014,
              <https://www.rfc-editor.org/info/rfc7234>.

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <https://www.rfc-editor.org/info/rfc7258>.

   [RFC7348]  Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
              L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
              eXtensible Local Area Network (VXLAN): A Framework for
              Overlaying Virtualized Layer 2 Networks over Layer 3
              Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
              <https://www.rfc-editor.org/info/rfc7348>.

   [RFC7435]  Dukhovni, V., "Opportunistic Security: Some Protection
              Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
              December 2014, <https://www.rfc-editor.org/info/rfc7435>.






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   [RFC7457]  Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
              Known Attacks on Transport Layer Security (TLS) and
              Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC7457,
              February 2015, <https://www.rfc-editor.org/info/rfc7457>.

   [RFC7489]  Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
              Message Authentication, Reporting, and Conformance
              (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
              <https://www.rfc-editor.org/info/rfc7489>.

   [RFC7498]  Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for
              Service Function Chaining", RFC 7498,
              DOI 10.17487/RFC7498, April 2015,
              <https://www.rfc-editor.org/info/rfc7498>.

   [RFC7525]  Sheffer, Y., Holz, R., and P. Saint-Andre,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
              2015, <https://www.rfc-editor.org/info/rfc7525>.

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,
              <https://www.rfc-editor.org/info/rfc7540>.

   [RFC7619]  Smyslov, V. and P. Wouters, "The NULL Authentication
              Method in the Internet Key Exchange Protocol Version 2
              (IKEv2)", RFC 7619, DOI 10.17487/RFC7619, August 2015,
              <https://www.rfc-editor.org/info/rfc7619>.

   [RFC7624]  Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
              Trammell, B., Huitema, C., and D. Borkmann,
              "Confidentiality in the Face of Pervasive Surveillance: A
              Threat Model and Problem Statement", RFC 7624,
              DOI 10.17487/RFC7624, August 2015,
              <https://www.rfc-editor.org/info/rfc7624>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <https://www.rfc-editor.org/info/rfc7665>.

   [RFC7754]  Barnes, R., Cooper, A., Kolkman, O., Thaler, D., and E.
              Nordmark, "Technical Considerations for Internet Service
              Blocking and Filtering", RFC 7754, DOI 10.17487/RFC7754,
              March 2016, <https://www.rfc-editor.org/info/rfc7754>.




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   [RFC7799]  Morton, A., "Active and Passive Metrics and Methods (with
              Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
              May 2016, <https://www.rfc-editor.org/info/rfc7799>.

   [RFC7826]  Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M.,
              and M. Stiemerling, Ed., "Real-Time Streaming Protocol
              Version 2.0", RFC 7826, DOI 10.17487/RFC7826, December
              2016, <https://www.rfc-editor.org/info/rfc7826>.

   [RFC7838]  Nottingham, M., McManus, P., and J. Reschke, "HTTP
              Alternative Services", RFC 7838, DOI 10.17487/RFC7838,
              April 2016, <https://www.rfc-editor.org/info/rfc7838>.

   [RFC7858]  Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
              and P. Hoffman, "Specification for DNS over Transport
              Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
              2016, <https://www.rfc-editor.org/info/rfc7858>.

   [RFC8073]  Moriarty, K. and M. Ford, "Coordinating Attack Response at
              Internet Scale (CARIS) Workshop Report", RFC 8073,
              DOI 10.17487/RFC8073, March 2017,
              <https://www.rfc-editor.org/info/rfc8073>.

   [RFC8164]  Nottingham, M. and M. Thomson, "Opportunistic Security for
              HTTP/2", RFC 8164, DOI 10.17487/RFC8164, May 2017,
              <https://www.rfc-editor.org/info/rfc8164>.

   [RFC8165]  Hardie, T., "Design Considerations for Metadata
              Insertion", RFC 8165, DOI 10.17487/RFC8165, May 2017,
              <https://www.rfc-editor.org/info/rfc8165>.

   [RFC8250]  Elkins, N., Hamilton, R., and M. Ackermann, "IPv6
              Performance and Diagnostic Metrics (PDM) Destination
              Option", RFC 8250, DOI 10.17487/RFC8250, September 2017,
              <https://www.rfc-editor.org/info/rfc8250>.

   [RFC8274]  Kampanakis, P. and M. Suzuki, "Incident Object Description
              Exchange Format Usage Guidance", RFC 8274,
              DOI 10.17487/RFC8274, November 2017,
              <https://www.rfc-editor.org/info/rfc8274>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.






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   [RFC8336]  Nottingham, M. and E. Nygren, "The ORIGIN HTTP/2 Frame",
              RFC 8336, DOI 10.17487/RFC8336, March 2018,
              <https://www.rfc-editor.org/info/rfc8336>.

   [SACM]     IETF, "Security Automation and Continuous Monitoring
              (sacm)", <https://datatracker.ietf.org/wg/sacm/charter/>.

   [SNI-TLS]  Huitema, C. and E. Rescorla, "Issues and Requirements for
              SNI Encryption in TLS", Work in Progress, draft-ietf-tls-
              sni-encryption-03, May 2018.

   [Snowden]  Verble, J., "The NSA and Edward Snowden: Surveillance in
              the 21st Century", SIGCAS Computer & Society, Vol. 44,
              No. 3, DOI 10.1145/2684097.2684101, September 2014,
              <http://www.jjsylvia.com/bigdatacourse/wp-content/
              uploads/2016/04/p14-verble-1.pdf>.

   [TCPcrypt]
              IETF, "TCP Increased Security (tcpinc)",
              <https://datatracker.ietf.org/wg/tcpinc/charter>.

   [TS3GPP]   3GPP, "Non-Access-Stratum (NAS) protocol for Evolved
              Packet System (EPS); Stage 3", 3GPP TS 24.301, version
              15.2.0, March 2018.

   [UPCON]    3GPP, "User Plane Congestion Management", 3GPP Rel-13,
              September 2014, <http://www.3gpp.org/DynaReport/
              FeatureOrStudyItemFile-570029.htm>.

   [UserData]
              Durumeric, Z., Ma, Z., Springall, D., Barnes, R.,
              Sullivan, N., Bursztein, E., Bailey, M., Alex Halderman,
              J., and V. Paxson, "The Security Impact of HTTPS
              Interception", Network and Distributed Systems Symposium,
              February 2017,
              <http://dx.doi.org/10.14722/ndss.2017.23456>.















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Acknowledgements

   Thanks to our reviewers, Natasha Rooney, Kevin Smith, Ashutosh Dutta,
   Brandon Williams, Jean-Michel Combes, Nalini Elkins, Paul Barrett,
   Badri Subramanyan, Igor Lubashev, Suresh Krishnan, Dave Dolson,
   Mohamed Boucadair, Stephen Farrell, Warren Kumari, Alia Atlas, Roman
   Danyliw, Mirja Kuehlewind, Ines Robles, Joe Clarke, Kyle Rose,
   Christian Huitema, and Chris Morrow for their editorial and content
   suggestions.  Surya K. Kovvali provided material for Section 7.
   Chris Morrow and Nik Teague provided reviews and updates specific to
   the DoS fingerprinting text.  Brian Trammell provided the IPFIX text.

Authors' Addresses

   Kathleen Moriarty (editor)
   Dell EMC
   176 South St
   Hopkinton, MA
   United States of America

   Email: Kathleen.Moriarty@dell.com


   Al Morton (editor)
   AT&T Labs
   200 Laurel Avenue South
   Middletown, NJ  07748
   United States of America

   Phone: +1 732 420 1571
   Fax:   +1 732 368 1192
   Email: acm@research.att.com



















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