path: root/doc/rfc/rfc8253.txt

Internet Engineering Task Force (IETF)                          D. Lopez
Request for Comments: 8253                           O. Gonzalez de Dios
Updates: 5440                                             Telefonica I+D
Category: Standards Track                                          Q. Wu
ISSN: 2070-1721                                                 D. Dhody
                                                                  Huawei
                                                            October 2017


       PCEPS: Usage of TLS to Provide a Secure Transport for the
         Path Computation Element Communication Protocol (PCEP)

Abstract

   The Path Computation Element Communication Protocol (PCEP) defines
   the mechanisms for the communication between a Path Computation
   Client (PCC) and a Path Computation Element (PCE), or among PCEs.
   This document describes PCEPS -- the usage of Transport Layer
   Security (TLS) to provide a secure transport for PCEP.  The
   additional security mechanisms are provided by the transport protocol
   supporting PCEP; therefore, they do not affect the flexibility and
   extensibility of PCEP.

   This document updates RFC 5440 in regards to the PCEP initialization
   phase procedures.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in 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/rfc8253.












Lopez, et al.                Standards Track                    [Page 1]
^L
RFC 8253                          PCEPS                     October 2017


Copyright Notice

   Copyright (c) 2017 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
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may
   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

























Lopez, et al.                Standards Track                    [Page 2]
^L
RFC 8253                          PCEPS                     October 2017


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   5
   3.  Applying PCEPS  . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.2.  Initiating TLS Procedures . . . . . . . . . . . . . . . .   5
     3.3.  The StartTLS Message  . . . . . . . . . . . . . . . . . .   8
     3.4.  TLS Connection Establishment  . . . . . . . . . . . . . .  13
     3.5.  Peer Identity . . . . . . . . . . . . . . . . . . . . . .  15
     3.6.  Connection Establishment Failure  . . . . . . . . . . . .  16
   4.  Discovery Mechanisms  . . . . . . . . . . . . . . . . . . . .  16
     4.1.  DANE Applicability  . . . . . . . . . . . . . . . . . . .  17
   5.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .  17
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
     6.1.  New PCEP Message  . . . . . . . . . . . . . . . . . . . .  18
     6.2.  New Error-Values  . . . . . . . . . . . . . . . . . . . .  19
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   8.  Manageability Considerations  . . . . . . . . . . . . . . . .  20
     8.1.  Control of Function and Policy  . . . . . . . . . . . . .  20
     8.2.  Information and Data Models . . . . . . . . . . . . . . .  21
     8.3.  Liveness Detection and Monitoring . . . . . . . . . . . .  21
     8.4.  Verifying Correct Operations  . . . . . . . . . . . . . .  21
     8.5.  Requirements on Other Protocols . . . . . . . . . . . . .  22
     8.6.  Impact on Network Operation . . . . . . . . . . . . . . .  22
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  22
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  22
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  23
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26





















Lopez, et al.                Standards Track                    [Page 3]
^L
RFC 8253                          PCEPS                     October 2017


1.  Introduction

   The Path Computation Element Communication Protocol (PCEP) [RFC5440]
   defines the mechanisms for the communication between a Path
   Computation Client (PCC) and a Path Computation Element (PCE), or
   between two PCEs.  These interactions include requests and replies
   that can be critical for a sustainable network operation and adequate
   resource allocation; therefore, appropriate security becomes a key
   element in the PCE infrastructure.  As the applications of the PCE
   framework evolve and more complex service patterns emerge, the
   definition of a secure mode of operation becomes more relevant.

   The Security Considerations section of [RFC5440] analyzes the
   potential threats to PCEP and their consequences; it also discusses
   several mechanisms for protecting PCEP against security attacks,
   without making a specific recommendation on a particular one or
   defining their application in depth.  Moreover, [RFC6952] states the
   importance of ensuring PCEP communication confidentiality, especially
   when PCEP communication endpoints do not reside in the same
   Autonomous System (AS), as the interception of PCEP messages could
   leak sensitive information related to computed paths and resources.

   Transport Layer Security (TLS) [RFC5246] is one of the solutions that
   seems most adequate among those mentioned in these documents, as it
   provides support for peer authentication, message encryption, and
   integrity.  TLS provides well-known mechanisms to support key
   configuration and exchange, as well as means to perform security
   checks on the results of PCE Discovery (PCED) procedures via the
   Interior Gateway Protocol (IGP) [RFC5088] [RFC5089].

   This document describes a security container for the transport of
   PCEP messages; therefore, it does not affect the flexibility and
   extensibility of PCEP.

   This document describes how to apply TLS to secure interactions with
   PCE, including initiation of the TLS procedures, the TLS handshake
   mechanism, the TLS methods for peer authentication, the applicable
   TLS ciphersuites for data exchange, and the handling of errors in the
   security checks.  In the rest of this document, we refer to this
   usage of TLS to provide a secure transport for PCEP as "PCEPS".

   Within this document, PCEP communications are described through a
   PCC-PCE relationship.  The PCE architecture also supports PCE-PCE
   communication; this is achieved by requesting the PCE to fill the
   role of a PCC, as usual.  Thus, in this document, the PCC refers to a
   PCC or a PCE initiating the PCEP session and acting as a client.





Lopez, et al.                Standards Track                    [Page 4]
^L
RFC 8253                          PCEPS                     October 2017


2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Applying PCEPS

3.1.  Overview

   The steps involved in establishing a PCEPS session are as follows:

   1.  Establishment of a TCP connection.

   2.  Initiation of the TLS procedures by the StartTLS message from PCE
       to PCC and from PCC to PCE.

   3.  Negotiation and establishment of a TLS connection.

   4.  Start exchange of PCEP messages as per [RFC5440].

   This document uses the standard StartTLS procedure in PCEP instead of
   using a different port for the secured session.  This is done to
   avoid requesting allocation of another port number for PCEPS.  The
   StartTLS procedure makes more efficient use of scarce port numbers
   and allows simpler configuration of PCEP.

   Implementations SHOULD follow the best practices and recommendations
   for using TLS, as per [RFC7525].

   It should be noted that this procedure updates what is defined in
   Sections 4.2.1 and 6.7 of [RFC5440] regarding the initialization
   phase and the processing of messages prior to the Open message.  The
   details of processing, including backward compatibility, are
   discussed in the following sections.

3.2.  Initiating TLS Procedures

   Since PCEP can operate either with or without TLS, it is necessary
   for a PCEP speaker to indicate whether it wants to set up a TLS
   connection or not.  For this purpose, this document specifies a new
   PCEP message called "StartTLS".  Thus, the PCEP session is secured
   via TLS from the start, before the exchange of any other PCEP message
   (including the Open message).  This document thus updates [RFC5440],
   which requires the Open message to be the first PCEP message that is
   exchanged.  In the case of a PCEP session using TLS, the StartTLS



Lopez, et al.                Standards Track                    [Page 5]
^L
RFC 8253                          PCEPS                     October 2017


   message will be sent first.  Also, a PCEP speaker that supports PCEPS
   MUST NOT start the OpenWait timer after the TCP establishment;
   instead, it starts a StartTLSWait timer as described in Section 3.3.

   The PCEP speaker MAY discover that the PCEP peer supports PCEPS or
   can be preconfigured to use PCEPS for a given peer (see Section 4 for
   more details).  An existing PCEP session cannot be secured via TLS;
   the session MUST be closed and re-established with TLS as per the
   procedure described in this document.

   The StartTLS message is a PCEP message sent by a PCC to a PCE and by
   a PCE to a PCC in order to initiate the TLS procedure for PCEP.  The
   PCC initiates the use of TLS by sending a StartTLS message.  The PCE
   agrees to the use of TLS by responding with its own StartTLS message.
   If the PCE is configured to only support TLS, it may send the
   StartTLS message immediately upon TCP connection establishment;
   otherwise, it MUST wait to see if the PCC's first message is an Open
   or a StartTLS message.  The TLS negotiation and establishment
   procedures are triggered once the PCEP speaker has sent and received
   the StartTLS message.  The Message-Type field of the PCEP common
   header for the StartTLS message is set to 13.

   Once the TCP connection has been successfully established, the first
   message sent by the PCC to the PCE and by the PCE to the PCC MUST be
   a StartTLS message for PCEPS.  Note that this is a significant change
   from [RFC5440], where the first PCEP message is the Open message.

   A PCEP speaker receiving a StartTLS message, after any other PCEP
   exchange has taken place (by receiving or sending any other messages
   from either side), MUST treat it as an unexpected message and reply
   with a PCEP Error (PCErr) message with Error-Type set to 25 (PCEP
   StartTLS failure) and Error-value set to 1 (Reception of StartTLS
   after any PCEP exchange), and it MUST close the TCP connection.

   Any message received prior to the StartTLS or Open message MUST
   trigger a protocol error condition causing a PCErr message to be sent
   with Error-Type set to 25 (PCEP StartTLS failure) and Error-value set
   to 2 (Reception of any other message apart from StartTLS, Open, or
   PCErr), and it MUST close the TCP connection.

   If the PCEP speaker that does not support PCEPS receives a StartTLS
   message, it will behave according to the existing error mechanism
   described in Section 6.2 of [RFC5440] (if the message is received
   prior to an Open message) or Section 6.9 of [RFC5440] (if an unknown
   message is received).  See Section 5 for more details.






Lopez, et al.                Standards Track                    [Page 6]
^L
RFC 8253                          PCEPS                     October 2017


   If the PCEP speaker that only supports PCEPS connections (as a local
   policy) receives an Open message, it MUST treat it as an unexpected
   message and reply with a PCErr message with Error-Type set to 1 (PCEP
   session establishment failure) and Error-value set to 1 (reception of
   an invalid Open message or a non Open message), and it MUST close the
   TCP connection.

   If a PCC supports PCEPS connections and allows non-PCEPS connections
   (as a local policy), it MUST first try to establish PCEPS by sending
   a StartTLS message, and in case it receives a PCErr message from the
   PCE, it MAY retry to establish a connection without PCEPS by sending
   an Open message.  If a PCE supports PCEPS connections and allows
   non-PCEPS connections (as a local policy), it MUST wait to respond
   after TCP establishment, based on the message received from the PCC.
   In case of a StartTLS message, the PCE MUST respond by sending a
   StartTLS message and moving to TLS establishment procedures as
   described in this document.  In case of an Open message, the PCE MUST
   respond with an Open message and move to the PCEP session
   establishment procedure as per [RFC5440].  If a PCE supports PCEPS
   connections only (as a local policy), it MAY send a StartTLS message
   to the PCC without waiting to receive a StartTLS message from the
   PCC.

   If a PCEP speaker that is unwilling or unable to negotiate TLS
   receives a StartTLS message, it MUST return a PCErr message (in the
   clear) with Error-Type set to 25 (PCEP StartTLS failure) and Error-
   value set to:

   o  3 (Failure, connection without TLS is not possible) if it is not
      willing to exchange PCEP messages without the solicited TLS
      connection, and it MUST close the TCP session.

   o  4 (Failure, connection without TLS is possible) if it is willing
      to exchange PCEP messages without the solicited TLS connection,
      and it MUST close the TCP session.  The receiver MAY choose to
      attempt to re-establish the PCEP session without TLS next.
      Re-establishing the PCEP session without TLS SHOULD be limited to
      only one attempt.

   If the PCEP speaker supports PCEPS and can establish a TLS
   connection, it MUST start the TLS connection negotiation and
   establishment steps described in Section 3.4 before the PCEP
   initialization procedure (see Section 4.2.1 of [RFC5440]).

   After the exchange of StartTLS messages, if the TLS negotiation fails
   for some reason (e.g., the required mechanisms for certificate
   revocation checking are not available), both peers MUST immediately
   close the connection.



Lopez, et al.                Standards Track                    [Page 7]
^L
RFC 8253                          PCEPS                     October 2017


   A PCEP speaker that does not support PCEPS sends the Open message
   directly, as per [RFC5440].  A PCEP speaker that supports PCEPS, but
   has learned in the last exchange the peer's willingness to
   re-establish the session without TLS, MAY send the Open message
   directly, as per [RFC5440].  Re-establishing the PCEP session without
   TLS SHOULD be limited to only one attempt.

   Given the asymmetric nature of TLS for connection establishment, it
   is relevant to identify the roles of each of the PCEP peers in it.
   The PCC SHALL act as the TLS client, and the PCE SHALL act as the TLS
   server as per [RFC5246].

   As per the recommendation from [RFC7525] to avoid downgrade attacks,
   PCEP peers that support PCEPS SHOULD default to strict TLS
   configuration, i.e., not allowing non-TLS PCEP sessions to be
   established.  PCEPS implementations MAY provide an option to allow
   the operator to manually override strict TLS configuration and allow
   unsecured connections.  Execution of this override SHOULD trigger a
   warning about the security implications of permitting unsecured
   connections.

3.3.  The StartTLS Message

   The StartTLS message is used to initiate the TLS procedure for a
   PCEPS session between the PCEP peers.  A PCEP speaker sends the
   StartTLS message to request negotiation and establishment of a TLS
   connection for PCEP.  On receiving a StartTLS message from the PCEP
   peer (i.e., when the PCEP speaker has sent and received the StartTLS
   message), it is ready to start the negotiation and establishment of
   TLS and move to the steps described in Section 3.4.

   The collision resolution procedures described in [RFC5440] for the
   exchange of Open messages MUST be applied by the PCEP peers during
   the exchange of StartTLS messages.

   The format of a StartTLS message is as follows:

      <StartTLS Message>::= <Common Header>

   The StartTLS message MUST contain only the PCEP common header with
   the Message-Type field set to 13.

   Once the TCP connection has been successfully established, the PCEP
   speaker MUST start a timer called the "StartTLSWait timer".  After
   the expiration of this timer, if neither the StartTLS message nor a
   PCErr/Open message (in case of failure and PCEPS not being supported
   by the peer, respectively) has been received, the PCEP speaker MUST
   send a PCErr message with Error-Type set to 25 (PCEP StartTLS



Lopez, et al.                Standards Track                    [Page 8]
^L
RFC 8253                          PCEPS                     October 2017


   failure) and Error-value set to 5 (No StartTLS message (nor PCErr/
   Open) before StartTLSWait timer expiry), and it MUST release the TCP
   connection.  A RECOMMENDED value for the StartTLSWait timer is 60
   seconds.  The value of the StartTLSWait timer MUST NOT be less than
   that of the OpenWait timer.

   The following figures illustrate the various interactions between a
   PCC and a PCE, based on the support for the PCEPS capability, during
   the PCEP session initialization.

                  +-+-+                 +-+-+
                  |PCC|                 |PCE|
                  +-+-+                 +-+-+
                    |                     |
                    | StartTLS            |
                    | msg                 |
                    |-------              |
                    |       \   StartTLS  |
                    |        \  msg       |
                    |         \  ---------|
                    |          \/         |
                    |          /\         |
                    |         /  -------->|
                    |        /            |
                    |<------              |
                    |:::::::::TLS:::::::::|
                    |:::::Establishment:::|
                    |                     |
                    |                     |
                    |:::::::PCEP::::::::::|
                    |                     |

            Figure 1: Both PCEP speakers support PCEPS (strict)


















Lopez, et al.                Standards Track                    [Page 9]
^L
RFC 8253                          PCEPS                     October 2017


                  +-+-+                 +-+-+
                  |PCC|                 |PCE|
                  +-+-+                 +-+-+
                    |                     |
                    | StartTLS            |
                    | msg                 |
                    |-------              |
                    |       \   StartTLS  |
                    |        \  msg       |
                    |         \  ---------|
                    |          \/         |
                    |          /\         |
                    |         /  -------->|
                    |        /            |
                    |<------              |
                    |:::::::::TLS:::::::::| TLS Establishment
                    |:::::Establishment:::| Failure; both
                    |                     | peers close
                                            the session

      Figure 2: Both PCEP speakers support PCEPS (strict) but cannot
                               establish TLS





























Lopez, et al.                Standards Track                   [Page 10]
^L
RFC 8253                          PCEPS                     October 2017


                  +-+-+                 +-+-+
                  |PCC|                 |PCE|
                  +-+-+                 +-+-+
                    |                     |  Does not support
                    | StartTLS            |  PCEPS and thus
                    | msg                 |  sends Open
                    |-------              |
                    |       \   Open      |
                    |        \  msg       |
                    |         \  ---------|
                    |          \/         |
                    |          /\         |
                    |         /  -------->|
                    |        /            |
                    |<------              |
                    |                     |
                    |<--------------------| Send Error
                    |       PCErr         | Type=1,Value=1
                    |                     | (non-Open message
                    |<--------------------|  received)
                    |       Close         |
                    ///////// TCP /////////
                    //////re-establish/////
          Send Open | Open                |
          this time | msg                 |
                    |-------              |
                    |       \   Open      |
                    |        \  msg       |
                    |         \  ---------|
                    |          \/         |
                    |          /\         |
                    |         /  -------->|
                    |        /            |
                    |<------              |

     Figure 3: PCE does not support connection with PCEPS, whereas PCC
                 supports connection with or without PCEPS














Lopez, et al.                Standards Track                   [Page 11]
^L
RFC 8253                          PCEPS                     October 2017


                  +-+-+                 +-+-+
                  |PCC|                 |PCE|
                  +-+-+                 +-+-+
                    |                     |
                    | StartTLS            |
                    | msg                 | PCE waits
                    |-------------------->| for PCC and
                    |            StartTLS | responds with
                    |<--------------------| Start TLS
                    |                     |
                    |:::::::::TLS:::::::::|
                    |:::::Establishment:::|
                    |                     |
                    |                     |
                    |:::::::PCEP::::::::::|
                    |                     |

   Figure 4: Both PCEP speakers support connection with or without PCEPS


                  +-+-+                 +-+-+
                  |PCC|                 |PCE|
                  +-+-+                 +-+-+
                    |                     |
                    | StartTLS            |
                    | msg                 | PCE waits
                    |-------------------->| for PCC
                    |               PCErr |
                    |<--------------------| Send Error
                    |                     | Type=25,Value=3
                    |                     | (Failure, connection
                    |<--------------------|  without TLS is not
                    |       Close         |  possible)

      Figure 5: Both PCEP speakers support connection with or without
                PCEPS, but PCE cannot start TLS negotiation















Lopez, et al.                Standards Track                   [Page 12]
^L
RFC 8253                          PCEPS                     October 2017


                  +-+-+                 +-+-+
                  |PCC|                 |PCE|
                  +-+-+                 +-+-+
                    |                     |
                    | Open                |
                    | msg                 | PCE waits
                    |-------------------->| for PCC and
                    |                Open | responds with
                    |<--------------------| Open
                    |                     |
                    |:::::::PCEP::::::::::|
                    |                     |

   Figure 6: PCE supports connection with or without PCEPS, whereas PCC
                  does not support connection with PCEPS

3.4.  TLS Connection Establishment

   Once the establishment of TLS has been agreed upon by the PCEP peers,
   the connection establishment SHALL follow the following steps:

   1.  Immediately negotiate a TLS session according to [RFC5246].  The
       following restrictions apply:

       *  Support for TLS v1.2 [RFC5246] or later is REQUIRED.

       *  Support for certificate-based mutual authentication is
          REQUIRED.

       *  Negotiation of a ciphersuite providing for integrity
          protection is REQUIRED.

       *  Negotiation of a ciphersuite providing for confidentiality is
          RECOMMENDED.

       *  Support for and negotiation of compression is OPTIONAL.

       *  PCEPS implementations MUST, at a minimum, support negotiation
          of the TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256 [RFC6460] and
          SHOULD support TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384 as
          well.  Implementations SHOULD support the NIST P-256
          (secp256r1) curve [RFC4492].  In addition, PCEPS
          implementations MUST support negotiation of the
          mandatory-to-implement ciphersuites required by the versions
          of TLS that they support from TLS 1.3 onwards.






Lopez, et al.                Standards Track                   [Page 13]
^L
RFC 8253                          PCEPS                     October 2017


   2.  Peer authentication can be performed in any of the following two
       REQUIRED operation models:

       *  TLS with X.509 certificates using Public-Key Infrastructure
          Exchange (PKIX) trust models:

          +  Implementations MUST allow the configuration of a list of
             trusted Certification Authorities (CAs) for incoming
             connections.

          +  Certificate validation MUST include the verification rules
             as per [RFC5280].

          +  PCEPS implementations SHOULD incorporate revocation methods
             (Certificate Revocation List (CRL) downloading, Online
             Certificate Status Protocol (OCSP), etc.) according to the
             trusted CA policies.

          +  Implementations SHOULD indicate their trusted CAs.  For TLS
             1.2, this is done using "certificate_authorities" on the
             server side (see Section 7.4.4 of [RFC5246]) and the
             "TrustedAuthorities" extension on the client side (see
             Section 6 of [RFC6066]).

          +  Implementations MUST follow the rules and guidelines for
             peer validation as defined in [RFC6125].  If an expected
             DNS name or IP address for the peer is configured, then the
             implementations MUST check them against the values in the
             presented certificate.  The DNS names and the IP addresses
             can be contained in the Common Name Identifier (CN-ID)
             [RFC6125] or the subjectAltName entries.  For verification,
             only one of these entries is considered.  The following
             precedence applies: for DNS name validation, DNS-ID
             [RFC6125] has precedence over CN-ID, and for IP address
             validation, subjectAltName:iPAddr has precedence over
             CN-ID.

          +  Implementations MAY allow the configuration of a set of
             additional properties of the certificate to check for a
             peer's authorization to communicate (e.g., a set of allowed
             values in URI-ID [RFC6125] or a set of allowed X.509 v3
             Certificate Policies).  The definitions of these properties
             are out of scope of this document.

       *  TLS with X.509 certificates using certificate fingerprints:
          Implementations MUST allow the configuration of a list of
          certificates that are trusted to identify peers, identified
          via the fingerprint of certificate octets encoded by the



Lopez, et al.                Standards Track                   [Page 14]
^L
RFC 8253                          PCEPS                     October 2017


          Distinguished Encoding Rules (DER).  Implementations MUST
          support SHA-256 as defined by [SHS] as the hash algorithm for
          the fingerprint, but a later revision may demand support for a
          stronger hash function.

   3.  Start exchanging PCEP messages.

       *  Once the TLS connection has been successfully established, the
          PCEP speaker MUST start the OpenWait timer [RFC5440]; after
          the expiration of this timer, if no Open message has been
          received, the PCEP speaker sends a PCErr message and releases
          the TCP/TLS connection.

3.5.  Peer Identity

   Depending on the peer authentication method in use, PCEPS supports
   different operation modes to establish a peer's identity and whether
   it is entitled to perform requests or can be considered authoritative
   in its replies.  PCEPS implementations SHOULD provide mechanisms for
   associating peer identities with different levels of access and/or
   authoritativeness, and they MUST provide a mechanism for establishing
   a default level for properly identified peers.  Any connection
   established with a peer that cannot be properly identified SHALL be
   terminated before any PCEP exchange takes place.

   In TLS X.509 mode using fingerprints, a peer is uniquely identified
   by the fingerprint of the presented certificate.

   There are numerous trust models in PKIX environments, and it is
   beyond the scope of this document to define how a particular
   deployment determines whether a peer is trustworthy.  Implementations
   that want to support a wide variety of trust models should expose as
   many details of the presented certificate to the administrator as
   possible so that the trust model can be implemented by the
   administrator.  At least the following parameters of the X.509
   certificate SHOULD be exposed:

   o  Peer's IP Address

   o  Peer's Fully Qualified Domain Name (FQDN)

   o  Certificate Fingerprint

   o  Issuer

   o  Subject

   o  All X.509 v3 Extended Key Usage



Lopez, et al.                Standards Track                   [Page 15]
^L
RFC 8253                          PCEPS                     October 2017


   o  All X.509 v3 Subject Alternative Name

   o  All X.509 v3 Certificate Policies

   Note that the remote IP address used for the TCP session
   establishment is also exposed.

   [RFC8232] specifies a Speaker Entity Identifier TLV
   (SPEAKER-ENTITY-ID) as an optional TLV that is included in the OPEN
   object.  It contains a unique identifier for the node that does not
   change during the lifetime of the PCEP speaker.  An implementation
   would thus expose the speaker entity identifier as part of the X.509
   v3 certificate's subjectAltName:otherName, so that an implementation
   could use this identifier for the peer identification trust model.

   In addition, a PCC MAY apply the procedures described in "DNS-Based
   Authentication of Named Entities (DANE)" [RFC6698] to verify its peer
   identity when using DNS discovery.  See Section 4.1 for further
   details.

3.6.  Connection Establishment Failure

   In case the initial TLS negotiation or the peer identity check fails,
   according to the procedures listed in this document, both peers MUST
   immediately close the connection.

   The initiator SHOULD follow the procedure listed in [RFC5440] to
   retry session setup as per the exponential back-off session
   establishment retry procedure.

4.  Discovery Mechanisms

   This document does not specify any discovery mechanism for support of
   PCEPS.  [PCE-DISCOVERY-PCEPS-SUPPORT] and [PCE-DISCOVERY-DNS] make
   the following proposals:

   o  A PCE can advertise its capability to support PCEPS using the
      IGP's advertisement mechanism of the PCED information.  The
      PCE-CAP-FLAGS sub-TLV is an optional sub-TLV used to advertise PCE
      capabilities.  It is present within the PCED sub-TLV carried by
      OSPF or IS-IS.  [RFC5088] and [RFC5089] provide the description
      and processing rules for this sub-TLV when carried within OSPF and
      IS-IS, respectively.  PCE capability bits are defined in
      [RFC5088].  A new capability flag bit for the PCE-CAP-FLAGS
      sub-TLV that can be announced as an attribute to distribute PCEP
      security support information is proposed in
      [PCE-DISCOVERY-PCEPS-SUPPORT].




Lopez, et al.                Standards Track                   [Page 16]
^L
RFC 8253                          PCEPS                     October 2017


   o  A PCE can advertise its capability to support PCEPS using DNS
      [PCE-DISCOVERY-DNS] by identifying the support of TLS.

4.1.  DANE Applicability

   DANE [RFC6698] defines a secure method to associate the certificate
   that is obtained from a TLS server with a domain name using DNS,
   i.e., using the TLSA DNS resource record (RR) to associate a TLS
   server certificate or public key with the domain name where the
   record is found, thus forming a "TLSA certificate association".  The
   DNS information needs to be protected by DNS Security (DNSSEC).  A
   PCC willing to apply DANE to verify server identity MUST conform to
   the rules defined in Section 4 of [RFC6698].  The implementation MUST
   support service certificate constraint (TLSA certificate usages type
   1) with Matching type 1 (SHA2-256) as described in [RFC6698] and
   [RFC7671].  The server's domain name must be authorized separately,
   as TLSA does not provide any useful authorization guarantees.

5.  Backward Compatibility

   The procedures described in this document define a security container
   for the transport of PCEP requests and replies carried by a TLS
   connection initiated by means of a specific extended message
   (StartTLS) that does not interfere with PCEP speaker implementations
   not supporting it.

   A PCC that does not support PCEPS will send an Open message as the
   first message on TCP establishment.  A PCE that only supports PCEPS
   will send a StartTLS message on TCP establishment.  The PCC would
   consider the received StartTLS message as an error and behave
   according to the existing error mechanism of [RFC5440], i.e., it
   would send a PCErr message with Error-Type 1 (PCEP session
   establishment failure) and Error-value 1 (reception of an invalid
   Open message or a non Open message) and close the session.

   A PCC that support PCEPS will send a StartTLS message as the first
   message on TCP establishment.  A PCE that does not support PCEPS
   would consider receiving a StartTLS message as an error, respond with
   a PCErr message with Error-Type 1 (PCEP session establishment
   failure) and Error-value 1 (reception of an invalid Open message or a
   non Open message), and close the session.

   If a StartTLS message is received at any other time by a PCEP speaker
   that does not implement PCEPS, it would consider it as an unknown
   message and would behave according to the existing error mechanism of
   [RFC5440], i.e., it would send a PCErr message with Error-Type 2
   (Capability not supported) and close the session.




Lopez, et al.                Standards Track                   [Page 17]
^L
RFC 8253                          PCEPS                     October 2017


   An existing PCEP session cannot be upgraded to PCEPS; the session
   needs to be terminated and re-established as per the procedure
   described in this document.  During the incremental upgrade, the PCEP
   speaker SHOULD allow session establishment with and without TLS.
   Once both PCEP speakers are upgraded to support PCEPS, the PCEP
   session is re-established with TLS; otherwise, a PCEP session without
   TLS is set up.  A redundant PCE MAY also be used during the
   incremental deployment to take over the PCE undergoing upgrade.  Once
   the upgrade is completed, support for the unsecured version SHOULD be
   removed.

   A PCE that accepts connections with or without PCEPS would respond
   based on the message received from the PCC.  A PCC that supports
   connection with or without PCEPS would first attempt to connect with
   PCEPS, and in case of error, it MAY retry to establish connection
   without PCEPS.  For successful TLS operations with PCEP, both PCEP
   peers in the network would need to be upgraded to support this
   document.

   Note that a PCEP implementation that supports PCEPS would respond
   with a PCErr message with Error-Type set to 25 (PCEP StartTLS
   failure) and Error-value set to 2 (Reception of any other message
   apart from StartTLS, Open, or PCErr) if any other message is sent
   before a StartTLS or Open message.  If the sender of the invalid
   message is a PCEP implementation that does not support PCEPS, it will
   not be able to understand this error.  A PCEPS implementation could
   also send the PCErr message as per [RFC5440] with Error-Type 1 (PCEP
   session establishment failure) and Error-value 1 (reception of an
   invalid Open message or a non Open message) before closing the
   session.

6.  IANA Considerations

6.1.  New PCEP Message

   The following new message type has been allocated within the "PCEP
   Messages" sub-registry of the "Path Computation Element Protocol
   (PCEP) Numbers" registry:

      Value      Description                    Reference
      -------------------------------------------------------
      13         StartTLS                       This document









Lopez, et al.                Standards Track                   [Page 18]
^L
RFC 8253                          PCEPS                     October 2017


6.2.  New Error-Values

   The following new error types and error values have been allocated
   within the "PCEP-ERROR Object Error Types and Values" sub-registry of
   the "Path Computation Element Protocol (PCEP) Numbers" registry:

   Error-Type   Meaning           Error-value             Reference
   ---------------------------------------------------------------------
    25          PCEP StartTLS     0: Unassigned            This document
                failure
                                  1: Reception of          This document
                                  StartTLS after
                                  any PCEP exchange

                                  2: Reception of          This document
                                  any other message
                                  apart from StartTLS,
                                  Open, or PCErr

                                  3: Failure, connection   This document
                                  without TLS is not
                                  possible

                                  4: Failure, connection   This document
                                  without TLS is
                                  possible

                                  5: No StartTLS message   This document
                                  (nor PCErr/Open)
                                  before StartTLSWait
                                  timer expiry

7.  Security Considerations

   While the application of TLS satisfies the requirement on
   confidentiality as well as fine-grained, policy-based peer
   authentication, there are security threats that it cannot address.
   It may be advisable to apply additional protection measures, in
   particular in what relates to attacks specifically addressed to
   forging the TCP connection underpinning TLS, especially in the case
   of long-lived connections.  One of these measures is the application
   of the TCP Authentication Option (TCP-AO) [RFC5925], which is fully
   compatible with and deemed as complementary to TLS.  The mechanisms
   to configure the requirements to use TCP-AO and other lower-layer
   protection measures with a particular peer are outside the scope of
   this document.





Lopez, et al.                Standards Track                   [Page 19]
^L
RFC 8253                          PCEPS                     October 2017


   Since computational resources required by the TLS handshake and
   ciphersuite are higher than unencrypted TCP, clients connecting to a
   PCEPS server can more easily create high-load conditions, and a
   malicious client might create a denial-of-service attack more easily.

   Some TLS ciphersuites only provide integrity validation of their
   payload and provide no encryption; such ciphersuites SHOULD NOT be
   used by default.  Administrators MAY allow the usage of these
   ciphersuites after careful weighting of the risk of relevant internal
   data leakage that can occur in such a case, as explicitly stated by
   [RFC6952].

   When using certificate fingerprints to identify PCEPS peers, any two
   certificates that produce the same hash value will be considered the
   same peer.  Therefore, it is important to make sure that the hash
   function used is cryptographically uncompromised, so that attackers
   are very unlikely to be able to produce a hash collision with a
   certificate of their choice.  This document mandates support for
   SHA-256 as defined by [SHS], but a later revision may demand support
   for stronger functions if suitable attacks on it are known.

   PCEPS implementations that continue to accept connections without TLS
   are susceptible to downgrade attacks as described in [RFC7457].  An
   attacker could attempt to remove the use of StartTLS messages that
   request the use of TLS as it pass on the wire in clear and could also
   attempt to inject a PCErr message that suggests attempting PCEP
   connection without TLS.

   The guidance given in [RFC7525] SHOULD be followed to avoid attacks
   on TLS.

8.  Manageability Considerations

   All manageability requirements and considerations listed in [RFC5440]
   apply to PCEP protocol extensions defined in this document.  In
   addition, requirements and considerations listed in this section
   apply.

8.1.  Control of Function and Policy

   A PCE or PCC implementation SHOULD allow configuring the PCEP
   security via TLS capabilities as described in this document.

   A PCE or PCC implementation supporting PCEP security via TLS MUST
   support general TLS configuration as per [RFC5246].  At least the
   configuration of one of the trust models and its corresponding
   parameters, as described in Sections 3.4 and 3.5, MUST be supported
   by the implementation.



Lopez, et al.                Standards Track                   [Page 20]
^L
RFC 8253                          PCEPS                     October 2017


   A PCEPS implementation SHOULD allow configuring the StartTLSWait
   timer value.

   PCEPS implementations MAY provide an option to allow the operator to
   manually override strict TLS configuration and allow unsecure
   connections.  Execution of this override SHOULD trigger a warning
   about the security implications of permitting unsecure connections.

   Further, the operator needs to develop suitable security policies
   around PCEP within his network.  The PCEP peers SHOULD provide ways
   for the operator to complete the following tasks in regards to a PCEP
   session:

   o  Determine if a session is protected via PCEPS.

   o  Determine the version of TLS, the mechanism used for
      authentication, and the ciphersuite in use.

   o  Determine if the certificate could not be verified and the reason
      for this circumstance.

   o  Inspect the certificate offered by the PCEP peer.

   o  Be warned if the StartTLS procedure fails for the PCEP peers that
      are known to support PCEPS via configurations or capability
      advertisements.

8.2.  Information and Data Models

   The PCEP MIB module is defined in [RFC7420].  The MIB module could be
   extended to include the ability to view the PCEPS capability,
   TLS-related information, and the TLS status for each PCEP peer.

   Further, to allow the operator to configure the PCEPS capability and
   various TLS-related parameters as well as to view the current TLS
   status for a PCEP session, the PCEP YANG module [PCEP-YANG] is
   extended to include TLS-related information.

8.3.  Liveness Detection and Monitoring

   Mechanisms defined in this document do not imply any new liveness
   detection and monitoring requirements in addition to those already
   listed in [RFC5440] and [RFC5246].

8.4.  Verifying Correct Operations

   A PCEPS implementation SHOULD log error events and provide PCEPS
   failure statistics with reasons.



Lopez, et al.                Standards Track                   [Page 21]
^L
RFC 8253                          PCEPS                     October 2017


8.5.  Requirements on Other Protocols

   Mechanisms defined in this document do not imply any new requirements
   on other protocols.  Note that Section 4 lists possible discovery
   mechanisms for support of PCEPS.

8.6.  Impact on Network Operation

   Mechanisms defined in this document do not have any significant
   impact on network operations in addition to those already listed in
   [RFC5440] and on the policy and management implications discussed
   above.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC6066]  Eastlake 3rd, D., "Transport Layer Security (TLS)
              Extensions: Extension Definitions", RFC 6066,
              DOI 10.17487/RFC6066, January 2011,
              <https://www.rfc-editor.org/info/rfc6066>.









Lopez, et al.                Standards Track                   [Page 22]
^L
RFC 8253                          PCEPS                     October 2017


   [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
              Verification of Domain-Based Application Service Identity
              within Internet Public Key Infrastructure Using X.509
              (PKIX) Certificates in the Context of Transport Layer
              Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
              2011, <https://www.rfc-editor.org/info/rfc6125>.

   [RFC6698]  Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
              2012, <https://www.rfc-editor.org/info/rfc6698>.

   [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>.

   [RFC7671]  Dukhovni, V. and W. Hardaker, "The DNS-Based
              Authentication of Named Entities (DANE) Protocol: Updates
              and Operational Guidance", RFC 7671, DOI 10.17487/RFC7671,
              October 2015, <https://www.rfc-editor.org/info/rfc7671>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [SHS]      National Institute of Standards and Technology, "Secure
              Hash Standard (SHS)", FIPS PUB 180-4,
              DOI 10.6028/NIST.FIPS.180-4, August 2015,
              <http://nvlpubs.nist.gov/nistpubs/FIPS/
              NIST.FIPS.180-4.pdf>.

9.2.  Informative References

   [PCE-DISCOVERY-DNS]
              Wu, Q., Dhody, D., King, D., Lopez, D., and J. Tantsura,
              "Path Computation Element (PCE) Discovery using Domain
              Name System(DNS)", Work in Progress, draft-wu-pce-dns-pce-
              discovery-10, March 2017.

   [PCE-DISCOVERY-PCEPS-SUPPORT]
              Lopez, D., Wu, Q., Dhody, D., Wang, Z., and D. King, "IGP
              extension for PCEP security capability support in the PCE
              discovery", Work in Progress, draft-wu-pce-discovery-
              pceps-support-07, March 2017.





Lopez, et al.                Standards Track                   [Page 23]
^L
RFC 8253                          PCEPS                     October 2017


   [PCEP-YANG]
              Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A
              YANG Data Model for Path Computation Element
              Communications Protocol (PCEP)", Work in Progress,
              draft-ietf-pce-pcep-yang-05, July 2017.

   [RFC4492]  Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
              Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
              for Transport Layer Security (TLS)", RFC 4492,
              DOI 10.17487/RFC4492, May 2006,
              <https://www.rfc-editor.org/info/rfc4492>.

   [RFC4513]  Harrison, R., Ed., "Lightweight Directory Access Protocol
              (LDAP): Authentication Methods and Security Mechanisms",
              RFC 4513, DOI 10.17487/RFC4513, June 2006,
              <https://www.rfc-editor.org/info/rfc4513>.

   [RFC5088]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "OSPF Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5088, DOI 10.17487/RFC5088,
              January 2008, <https://www.rfc-editor.org/info/rfc5088>.

   [RFC5089]  Le Roux, JL., Ed., Vasseur, JP., Ed., Ikejiri, Y., and R.
              Zhang, "IS-IS Protocol Extensions for Path Computation
              Element (PCE) Discovery", RFC 5089, DOI 10.17487/RFC5089,
              January 2008, <https://www.rfc-editor.org/info/rfc5089>.

   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC6460]  Salter, M. and R. Housley, "Suite B Profile for Transport
              Layer Security (TLS)", RFC 6460, DOI 10.17487/RFC6460,
              January 2012, <https://www.rfc-editor.org/info/rfc6460>.

   [RFC6614]  Winter, S., McCauley, M., Venaas, S., and K. Wierenga,
              "Transport Layer Security (TLS) Encryption for RADIUS",
              RFC 6614, DOI 10.17487/RFC6614, May 2012,
              <https://www.rfc-editor.org/info/rfc6614>.

   [RFC6952]  Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
              BGP, LDP, PCEP, and MSDP Issues According to the Keying
              and Authentication for Routing Protocols (KARP) Design
              Guide", RFC 6952, DOI 10.17487/RFC6952, May 2013,
              <https://www.rfc-editor.org/info/rfc6952>.






Lopez, et al.                Standards Track                   [Page 24]
^L
RFC 8253                          PCEPS                     October 2017


   [RFC7420]  Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
              Hardwick, "Path Computation Element Communication Protocol
              (PCEP) Management Information Base (MIB) Module",
              RFC 7420, DOI 10.17487/RFC7420, December 2014,
              <https://www.rfc-editor.org/info/rfc7420>.

   [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>.

   [RFC8232]  Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
              and D. Dhody, "Optimizations of Label Switched Path State
              Synchronization Procedures for a Stateful PCE", RFC 8232,
              DOI 10.17487/RFC8232, September 2017,
              <https://www.rfc-editor.org/info/rfc8232>.

Acknowledgements

   This specification relies on the analysis and profiling of TLS
   included in [RFC6614] and the procedures described for the StartTLS
   command in [RFC4513].

   We would like to thank Joe Touch for his suggestions and support
   regarding the StartTLS mechanisms.

   Thanks to Daniel King for reminding the authors about manageability
   considerations.

   Thanks to Cyril Margaria for shepherding this document.

   Thanks to David Mandelberg for early SECDIR review comments as well
   as further review during IETF last call.

   Thanks to Dan Frost for the RTGDIR review and comments.

   Thanks to Dale Worley for the Gen-ART review and comments.

   Thanks to Tianran Zhou for the OPSDIR review.

   Thanks to Deborah Brungard for being the responsible AD and guiding
   the authors as needed.

   Also, thanks to Mirja Kuhlewind, Eric Rescorla, Warren Kumari,
   Kathleen Moriarty, Suresh Krishnan, Ben Campbell, and Alexey Melnikov
   for the IESG review and comments.





Lopez, et al.                Standards Track                   [Page 25]
^L
RFC 8253                          PCEPS                     October 2017


Authors' Addresses

   Diego R. Lopez
   Telefonica I+D
   Don Ramon de la Cruz, 82
   Madrid  28006
   Spain

   Phone: +34 913 129 041
   Email: diego.r.lopez@telefonica.com


   Oscar Gonzalez de Dios
   Telefonica I+D
   Don Ramon de la Cruz, 82
   Madrid  28006
   Spain

   Phone: +34 913 129 041
   Email: oscar.gonzalezdedios@telefonica.com


   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: sunseawq@huawei.com


   Dhruv Dhody
   Huawei
   Divyashree Techno Park, Whitefield
   Bangalore, KA  560066
   India

   Email: dhruv.ietf@gmail.com













Lopez, et al.                Standards Track                   [Page 26]
^L