path: root/doc/rfc/rfc5979.txt

Internet Engineering Task Force (IETF)                           C. Shen
Request for Comments: 5979                                H. Schulzrinne
Category: Experimental                                       Columbia U.
ISSN: 2070-1721                                                   S. Lee
                                                                 Samsung
                                                                 J. Bang
                                                             Samsung AIT
                                                              March 2011


                     NSIS Operation over IP Tunnels

Abstract

   NSIS Quality of Service (QoS) signaling enables applications to
   perform QoS reservation along a data flow path.  When the data flow
   path contains IP tunnel segments, NSIS QoS signaling has no effect
   within those tunnel segments.  Therefore, the resulting tunnel
   segments could become the weakest QoS link and invalidate the QoS
   efforts in the rest of the end-to-end path.  The problem with NSIS
   signaling within the tunnel is caused by the tunnel encapsulation
   that masks packets' original IP header fields.  Those original IP
   header fields are needed to intercept NSIS signaling messages and
   classify QoS data packets.  This document defines a solution to this
   problem by mapping end-to-end QoS session requests to corresponding
   QoS sessions in the tunnel, thus extending the end-to-end QoS
   signaling into the IP tunnel segments.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  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).  Not
   all documents approved by the IESG are a candidate for any level of
   Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc5979.






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Copyright Notice

   Copyright (c) 2011 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
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   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
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   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.

























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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Problem Statement  . . . . . . . . . . . . . . . . . . . . . .  6
     3.1.  IP Tunneling Protocols . . . . . . . . . . . . . . . . . .  6
     3.2.  NSIS QoS Signaling in the Presence of IP Tunnels . . . . .  7
   4.  Design Overview  . . . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  Design Requirements  . . . . . . . . . . . . . . . . . . . 10
     4.2.  Overall Design Approach  . . . . . . . . . . . . . . . . . 11
     4.3.  Tunnel Flow ID for Different IP Tunneling Protocols  . . . 13
   5.  NSIS Operation over Tunnels with Preconfigured QoS Sessions  . 14
     5.1.  Sender-initiated Reservation . . . . . . . . . . . . . . . 14
     5.2.  Receiver-Initiated Reservation . . . . . . . . . . . . . . 15
   6.  NSIS Operation over Tunnels with Dynamically Created QoS
       Sessions . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     6.1.  Sender-Initiated Reservation . . . . . . . . . . . . . . . 17
     6.2.  Receiver-Initiated Reservation . . . . . . . . . . . . . . 19
   7.  NSIS-Tunnel Signaling Capability Discovery . . . . . . . . . . 22
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 24
   10. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 24
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 25
     11.2. Informative References . . . . . . . . . . . . . . . . . . 25

1.  Introduction

   IP tunneling [RFC1853] [RFC2003] is a technique that allows a packet
   to be encapsulated and carried as payload within an IP packet.  The
   resulting encapsulated packet is called an IP tunnel packet, and the
   packet being tunneled is called the original packet.  In typical
   scenarios, IP tunneling is used to exert explicit forwarding path
   control (e.g., in Mobile IP [RFC5944]), implement secure IP data
   delivery (e.g., in IPsec [RFC4301]), and help packet routing in IP
   networks of different characteristics (e.g., between IPv6 and IPv4
   networks [RFC4213]).  Section 3.1 summarizes a list of common IP
   tunneling protocols.

   This document considers the situation when the packet being tunneled
   contains a Next Step In Signaling (NSIS) [RFC4080] packet.  NSIS is
   an IP signaling architecture consisting of a Generic Internet
   Signaling Transport (GIST) [RFC5971] sub-layer for signaling
   transport, and an NSIS Signaling Layer Protocol (NSLP) sub-layer
   customizable for different applications.  We focus on the Quality of
   Service (QoS) NSLP [RFC5974] which provides functionalities that
   extend those of the earlier RSVP [RFC2205] signaling.  In this
   document, the terms "NSIS" and "NSIS QoS" are used interchangeably.



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   Without additional efforts, NSIS signaling does not work within IP
   tunnel segments of a signaling path.  The reason is that tunnel
   encapsulation masks the original packet including its header and
   payload.  However, information from the original packet is required
   both for NSIS peer node discovery and for QoS data flow packet
   classification.  Without access to information from the original
   packet, an IP tunnel acts as an NSIS-unaware virtual link in the end-
   to-end NSIS signaling path.

   This document defines a mechanism to extend end-to-end NSIS signaling
   for QoS reservation into IP tunnels.  The NSIS-aware IP tunnel
   endpoints that support this mechanism are called NSIS-tunnel-aware
   endpoints.  There are two main operation modes.  On one hand, if the
   tunnel already has preconfigured QoS sessions, the NSIS-tunnel-aware
   endpoints map end-to-end QoS signaling requests directly to existing
   tunnel sessions as long as there are enough tunnel session resources;
   on the other hand, if no preconfigured tunnel QoS sessions are
   available, the NSIS-tunnel-aware endpoints dynamically initiate and
   maintain tunnel QoS sessions that are then associated with the
   corresponding end-to-end QoS sessions.  Note that whether or not the
   tunnel preconfigures QoS sessions, and which preconfigured tunnel QoS
   sessions a particular end-to-end QoS signaling request should be
   mapped to are policy issues that are out of scope of this document.

   The rest of this document is organized as follows.  Section 2 defines
   terminology.  Section 3 presents the problem statement including
   common IP tunneling protocols and existing behavior of NSIS QoS
   signaling over IP tunnels.  Section 4 introduces the design
   requirements and overall approach of our mechanism.  More details
   about how NSIS QoS signaling operates with tunnels that use
   preconfigured QoS and dynamic QoS signaling are provided in Sections
   5 and 6.  Section 7 describes a method to automatically discover
   whether a tunnel endpoint node supports the NSIS-tunnel
   interoperation mechanism defined in this document.  Section 8
   discusses IANA considerations, and Section 9 considers security.

2.  Terminology

   This document uses terminology defined in [RFC2473], [RFC5971], and
   [RFC5974].  In addition, the following terms are used:

   IP Tunnel:  A tunnel that is configured as a virtual link between two
      IP nodes and on which the encapsulating protocol is IP.

   Tunnel IP Header:  The IP header prepended to the original packet
      during encapsulation.  It specifies the tunnel endpoints as source
      and destination.




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   Tunnel-Specific Header:  The header fields inserted by the
      encapsulation mechanism after the tunnel IP header and before the
      original packet.  These headers may or may not exist depending on
      the specific tunnel mechanism used.  An example of such header
      fields is the Encapsulation Security Payload (ESP) header for
      IPsec [RFC4301] tunneling mode.

   Tunnel Intermediate Node (Tmid):  A node that resides in the middle
      of the forwarding path between the tunnel entry-point node and the
      tunnel exit-point node.

   Flow Identifier (Flow ID):  The set of header fields that is used to
      identify a data flow.  For example, it may include flow sender and
      receiver addresses, and protocol and port numbers.

   End-to-End QoS Signaling:  The signaling process that manipulates the
      QoS control information in the end-to-end path from the flow
      sender to the flow receiver.  When the end-to-end flow path
      contains tunnel segments, this document uses end-to-end QoS
      signaling to refer to the QoS signaling outside the tunnel
      segments.  This document uses "end-to-end QoS signaling" and "end-
      to-end signaling" interchangeably.

   Tunnel QoS Signaling:  The signaling process that manipulates the QoS
      control information in the path inside a tunnel, between the
      tunnel entry-point and the tunnel exit-point nodes.  This document
      uses "tunnel QoS signaling" and "tunnel signaling"
      interchangeably.

   NSIS-Aware Node:  A node that supports NSIS signaling.

   NSIS-Aware Tunnel Endpoint Node:  A tunnel endpoint node that is also
      an NSIS node.

   NSIS-Tunnel-Aware Endpoint Node:  An NSIS-aware tunnel endpoint node
      that also supports the mechanism for NSIS operating over IP
      tunnels defined in this document.














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3.  Problem Statement

3.1.  IP Tunneling Protocols

                    Tunnel from node B to node D
                     <---------------------->
                  Tunnel       Tunnel        Tunnel
                  Entry-Point  Intermediate  Exit-Point
                  Node         Node          Node
   +-+            +-+          +-+           +-+            +-+
   |A|-->--//-->--|B|=====>====|C|===//==>===|D|-->--//-->--|E|
   +-+            +-+          +-+           +-+            +-+
   Original                                                 Original
   Packet                                                   Packet
   Source                                                   Destination
   Node                                                     Node

                            Figure 1: IP Tunnel

   The following description about IP tunneling is derived from
   [RFC2473] and adapted for both IPv4 and IPv6.

   IP tunneling (Figure 1) is a technique for establishing a "virtual
   link" between two IP nodes for transmitting data packets as payloads
   of IP packets.  From the point of view of the two nodes, this
   "virtual link", called an IP tunnel, appears as a point-to-point link
   on which IP acts like a link-layer protocol.  The two IP nodes play
   specific roles.  One node encapsulates original packets received from
   other nodes or from itself and forwards the resulting tunnel packets
   through the tunnel.  The other node decapsulates the received tunnel
   packets and forwards the resulting original packets towards their
   destinations, possibly itself.  The encapsulating node is called the
   tunnel entry-point node (Tentry), and it is the source of the tunnel
   packets.  The decapsulating node is called the tunnel exit-point node
   (Texit), and it is the destination of the tunnel packets.

   An IP tunnel is a unidirectional mechanism - the tunnel packet flow
   takes place in one direction between the IP tunnel entry-point and
   exit-point nodes.  Bidirectional tunneling is achieved by combining
   two unidirectional mechanisms, that is, configuring two tunnels, each
   in opposite direction to the other -- the entry-point node of one
   tunnel is the exit-point node of the other tunnel.

   Figure 2 illustrates the original packet and the resulting tunnel
   packet.  In a tunnel packet, the original packet is encapsulated
   within the tunnel header.  The tunnel header contains two components,
   the tunnel IP header and other tunnel-specific headers.  The tunnel
   IP header specifies the tunnel entry-point node as the IP source



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   address and the tunnel exit-point node as the IP destination address,
   causing the tunnel packet to be forwarded in the tunnel.  The tunnel-
   specific header between the tunnel IP header and the original packet
   is optional, depending on the tunneling protocol in use.

                         +----------------------------------//-----+
                         | Original |                              |
                         |          |   Original Packet Payload    |
                         | Header   |                              |
                         +----------------------------------//-----+
                          <            Original Packet            >
                                               |
                                               v
    <  Tunnel Headers   > <            Original Packet            >
   +---------+-----------+-------------------------//--------------+
   | Tunnel  | Tunnel-   |                                         |
   | IP      | Specific  |             Original Packet             |
   | Header  | Header    |                                         |
   +---------+-----------+-------------------------//--------------+
    <                        Tunnel IP Packet                     >

                     Figure 2: IP Tunnel Encapsulation

   Commonly used IP tunneling protocols include Generic Routing
   Encapsulation (GRE) [RFC1701][RFC2784], Generic Routing Encapsulation
   over IPv4 Networks (GREIPv4) [RFC1702] and IP Encapsulation within IP
   (IPv4INIPv4) [RFC1853][RFC2003], Minimal Encapsulation within IP
   (MINENC) [RFC2004], IPv6 over IPv4 Tunneling (IPv6INIPv4) [RFC4213],
   Generic Packet Tunneling in IPv6 Specification (IPv6GEN) [RFC2473]
   and IPsec tunneling mode [RFC4301] [RFC4303].  Among these tunneling
   protocols, the tunnel headers in IPv4INIPv4, IPv6INIPv4, and IPv6GEN
   contain only a tunnel IP header, and no tunnel-specific header.  All
   the other tunneling protocols have a tunnel header consisting of both
   a tunnel IP header and a tunnel-specific header.  The tunnel-specific
   header is the GRE header for GRE and GREIPv4, the minimum
   encapsulation header for MINENC, and the ESP header for IPsec
   tunneling mode.  As will be discussed in Section 4.3, some of the
   tunnel-specific headers may be used to identify a flow in the tunnel
   and facilitate NSIS operating over IP tunnels.

3.2.  NSIS QoS Signaling in the Presence of IP Tunnels

   Typically, applications use NSIS QoS signaling to reserve resources
   for a flow along the flow path.  NSIS QoS signaling can be initiated
   by either the flow sender or flow receiver.  Figure 3 shows an
   example scenario with five NSIS nodes, including flow sender node A,
   flow receiver node E, and intermediate NSIS nodes B, C, and D.  Nodes
   that are not NSIS QoS capable are not shown.



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    NSIS QoS       NSIS QoS     NSIS QoS      NSIS QoS       NSIS QoS
    Node           Node         Node          Node           Node
    +-+            +-+          +-+           +-+            +-+
    |A|-->--//-->--|B|----->----|C|---//-->---|D|-->--//-->--|E|
    +-+            +-+          +-+           +-+            +-+
    Flow                                                     Flow
    Sender                                                   Receiver
    Node                                                     Node

             Figure 3: Example Scenario of NSIS QoS Signaling

   Figure 4 illustrates a sender-initiated signaling sequence in the
   scenario of Figure 3.  Sender node A sends a RESERVE message towards
   receiver node E.  The RESERVE message gets forwarded by intermediate
   NSIS Nodes B, C, and D and finally reaches receiver node E.  Receiver
   node E then sends back a RESPONSE message confirming the QoS
   reservation, again through the previous intermediate NSIS nodes in
   the flow path.

   There are two important aspects in the above signaling process that
   are worth mentioning.  First, the flow sender does not initially know
   exactly which intermediate nodes are NSIS-aware and should be
   involved in the signaling process for a flow from node A to node E.
    Discovery of those nodes (namely, nodes B, C, and D) is accomplished
   by a separate NSIS peer discovery process (not shown above; see
   [RFC5971]).  The NSIS peer discovery messages contain special IP
   header and payload formats or include a Router Alert Option (RAO)
   [RFC2113] [RFC2711].  The special formats of NSIS discovery messages
   allow nodes B, C, and D to intercept the messages and subsequently
   insert themselves into the signaling path for the flow in question.
   After formation of the signaling path, all signaling messages
   corresponding to this flow will be passed to these nodes for
   processing.  Other nodes that are not NSIS-aware simply forward all
   signaling messages, as they would any other IP packets that do not
   require additional handling.
















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    Node A         Node B         Node C         Node D         Node E
      |              |              |              |              |
      |   RESERVE    |              |              |              |
      +------------->|              |              |              |
      |              |   RESERVE    |              |              |
      |              +------------->|              |              |
      |              |              |   RESERVE    |              |
      |              |              +------------->|              |
      |              |              |              |   RESERVE    |
      |              |              |              +------------->|
      |              |              |              |   RESPONSE   |
      |              |              |              |<-------------+
      |              |              |   RESPONSE   |              |
      |              |              |<-------------+              |
      |              |   RESPONSE   |              |              |
      |              |<-------------+              |              |
      |   RESPONSE   |              |              |              |
      |<-------------+              |              |              |
      |              |              |              |              |
      |              |              |              |              |

               Figure 4: Sender-Initiated NSIS QoS Signaling

   Second, the goal of QoS signaling is to install control information
   to give QoS treatment for the flow being signaled.  Basic QoS control
   information includes the data Flow ID for packet classification and
   the type of QoS treatment those packets are entitled to.  The Flow ID
   contains a set of header fields such as flow sender and receiver
   addresses, and protocol and port numbers.

   Now consider Figure 5 where nodes B, C, and D are endpoints and
   intermediate nodes of an IP tunnel.  During the signaling path
   discovery process, node B can still intercept and process NSIS peer
   discovery messages if it recognizes them before performing tunnel
   encapsulation; node D can identify NSIS peer discovery messages after
   performing tunnel decapsulation.  A tunnel intermediate node such as
   node C, however, only sees the tunnel header of the packets and will
   not be able to identify the original NSIS peer discovery message or
   insert itself in the flow signaling path.  Furthermore, the Flow ID
   of the original flow is based on IP header fields of the original
   packet.  Those fields are also hidden in the payload of the tunnel
   packet.  So, there is no way node C can classify packets belonging to
   that flow in the tunnel.








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                     Tunnel from node B to node D
                      <---------------------->
                   Tunnel       Tunnel        Tunnel
                   Entry-Point  Intermediate  Exit-Point
    NSIS QoS       NSIS QoS     NSIS QoS      NSIS QoS       NSIS QoS
    Node           Node         Node          Node           Node
    +-+            +-+          +-+           +-+            +-+
    |A|-->--//-->--|B|=====>====|C|===//==>===|D|-->--//-->--|E|
    +-+            +-+          +-+           +-+            +-+
    Flow                                                     Flow
    Sender                                                   Receiver
    Node                                                     Node

      Figure 5: Example Scenario of NSIS QoS Signaling with IP Tunnel

   In summary, an IP tunnel segment normally appears like a QoS-unaware
   virtual link.  Since the best QoS of an end-to-end path is judged
   based on its weakest segment, we need a mechanism to extend NSIS into
   the IP tunnel segments, which should allow the tunnel intermediate
   nodes to intercept original NSIS signaling messages and classify
   original data flow packets in the presence of tunnel encapsulation.

4.  Design Overview

4.1.  Design Requirements

   We identify the following design requirements for NSIS operating over
   IP tunnels.

   o  The mechanism should work with all common IP tunneling protocols
      listed in Section 3.1.

   o  Some IP tunnels maintain preconfigured QoS sessions inside the
      tunnel.  The mechanism should work for IP tunnels both with and
      without preconfigured tunnel QoS sessions.

   o  The mechanism should minimize the required upgrade to existing
      infrastructure in order to facilitate its deployment.
      Specifically, we should limit the necessary upgrade to the tunnel
      endpoints.

   o  The mechanism should provide a method for one NSIS-tunnel-aware
      endpoint to discover whether the other endpoint is also NSIS-
      tunnel-aware, when necessary.

   o  The mechanism should learn from the design experience of previous
      related work on RSVP over IP tunnels (RSVP-TUNNEL) [RFC2746],
      while also addressing the following major differences of NSIS from



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      RSVP.  First, NSIS is designed as a generic framework to
      accommodate various signaling application needs, and therefore is
      split into a signaling transport layer and a signaling application
      layer; RSVP does not have a layer split and is designed only for
      QoS signaling.  Second, NSIS QoS NSLP allows both sender-initiated
      and receiver-initiated reservations; RSVP only supports receiver-
      initiated reservations.  Third, NSIS deals only with unicast; RSVP
      also supports multicast.  Fourth, NSIS integrates a new SESSION-ID
      feature which is different from the session identification concept
      in RSVP.

4.2.  Overall Design Approach

   The overall design of this NSIS signaling and IP tunnel interworking
   mechanism draws similar concepts from RSVP-TUNNEL [RFC2746], but is
   tailored and extended for NSIS operation.

   Since we only consider unidirectional flows, to accommodate flows in
   both directions of a tunnel, we require both tunnel entry-point and
   tunnel exit-point to be NSIS-tunnel-aware.  An NSIS-tunnel-aware
   endpoint knows whether the other tunnel endpoint is NSIS-tunnel-aware
   either through preconfiguration or through an NSIS-tunnel capability
   discovery mechanism defined in Section 7.

   Tunnel endpoints need to always intercept NSIS peer discovery
   messages and insert themselves into the NSIS signaling path so they
   can receive all NSIS signaling messages and coordinate their
   interaction with tunnel QoS.

   To facilitate QoS handling in the tunnel, an end-to-end QoS session
   is mapped to a tunnel QoS session, either preconfigured or
   dynamically created.  The tunnel session uses a tunnel Flow ID based
   on information available in the tunnel headers, thus allowing tunnel
   intermediate nodes to classify flow packets correctly.

   For tunnels that maintain preconfigured QoS sessions, upon receiving
   a request to reserve resources for an end-to-end session, the tunnel
   endpoint maps the end-to-end QoS session to an existing tunnel
   session.  To simplify the design, the mapping decision is always made
   by the tunnel entry-point, regardless of whether the end-to-end
   session uses sender-initiated or receiver-initiated NSIS signaling
   mode.  The details about which end-to-end session can be mapped to
   which preconfigured tunnel session depend on policy mechanisms
   outside the scope of this document.

   For tunnels that do not maintain preconfigured QoS sessions, the
   NSIS-tunnel-aware endpoints dynamically create and manage a
   corresponding tunnel QoS session for the end-to-end session.  Since



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   the initiation mode of both QoS sessions can be sender-initiated or
   receiver-initiated, to simplify the design, we require that the
   initiation mode of the tunnel QoS session follows that of the end-to-
   end QoS session.  In other words, the end-to-end QoS session and its
   corresponding tunnel QoS session are either both sender-initiated or
   both receiver-initiated.  To keep the handling mechanism consistent
   with the case for tunnels with preconfigured QoS sessions, the tunnel
   entry-point always initiates the mapping between the tunnel session
   and the end-to-end session.

   As the mapping initiator, the tunnel entry-point records the
   association between the end-to-end session and its corresponding
   tunnel session, both in tunnels with and without preconfigured QoS
   sessions.  This association serves two purposes, one for the
   signaling plane and the other for the data plane.  For the signaling
   plane, the association enables the tunnel entry-point to coordinate
   necessary interactions between the end-to-end and the tunnel QoS
   sessions, such as QoS adjustment in sender-initiated reservations.
   For the data plane, the association allows the tunnel entry-point to
   correctly encapsulate data flow packets according to the chosen
   tunnel Flow ID.  Since the tunnel Flow ID uses header fields that are
   visible inside the tunnel, the tunnel intermediate nodes can classify
   the data flow packets and apply appropriate QoS treatment.

   In addition to the tunnel entry-point recording the association
   between the end-to-end session and its corresponding tunnel session,
   the tunnel exit-point also needs to maintain the same association for
   similar reasons.  For the signaling plane, this association at the
   tunnel exit-point enables the interaction of the end-to-end and the
   tunnel QoS session such as QoS adjustment in receiver-initiated
   reservations.  For the data plane, this association tells the tunnel
   exit-point that the relevant data flow packets need to be
   decapsulated according to the corresponding tunnel Flow ID.

   In tunnels with preconfigured QoS sessions, the tunnel exit-point may
   also learn about the mapping information between the corresponding
   tunnel and end-to-end QoS sessions through preconfiguration as well.
   In tunnels without preconfigured QoS sessions, the tunnel exit-point
   knows the mapping between the corresponding tunnel and end-to-end QoS
   sessions through the NSIS signaling process that creates the tunnel
   QoS sessions inside the tunnel, with the help of appropriate QoS NSLP
   session-binding and message-binding mechanisms.

   One problem for NSIS operating over IP tunnels that dynamically
   create QoS sessions is that it involves two signaling sequences.  The
   outcome of the tunnel signaling session directly affects the outcome
   of the end-to-end signaling session.  Since the two signaling
   sessions overlap in time, there are circumstances when a tunnel



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   endpoint has to decide whether it should proceed with the end-to-end
   signaling session while it is still waiting for results of the tunnel
   session.  This problem can be addressed in two ways, namely
   sequential mode and parallel mode.  In sequential mode, end-to-end
   signaling pauses while it is waiting for results of tunnel signaling,
   and resumes upon receipt of the tunnel signaling outcome.  In
   parallel mode, end-to-end signaling continues outside the tunnel
   while tunnel signaling is still in process and its outcome is
   unknown.  The parallel mode may lead to reduced signaling delays if
   the QoS resources in the tunnel path are sufficient compared to the
   rest of the end-to-end path.  If the QoS resources in the tunnel path
   are more constraint than the rest of the end-to-end path, however,
   the parallel mode may lead to wasted end-to-end signaling or may
   necessitate renegotiation after the tunnel signaling outcome becomes
   available.  In those cases, the signaling flow of the parallel mode
   also tends to be complicated.  This document adopts a sequential mode
   approach for the two signaling sequences.

4.3.  Tunnel Flow ID for Different IP Tunneling Protocols

   A tunnel Flow ID identifies the end-to-end flow for packet
   classification within the tunnel.  The tunnel Flow ID is based on a
   set of tunnel header fields.  Different tunnel Flow IDs can be chosen
   for different tunneling mechanisms in order to minimize the
   classification overhead.  This document specifies the following Flow
   ID formats for the respective tunneling protocols.

   o  For IPv6 tunneling protocols (IPv6GEN), the tunnel Flow ID
      consists of the tunnel entry-point IPv6 address and the tunnel
      exit-point IPv6 address plus a unique IPv6 flow label [RFC3697].

   o  For IPsec tunnel mode (IPsec), the tunnel Flow ID contains the
      tunnel entry-point IP address and the tunnel exit-point IP address
      plus the Security Parameter Index (SPI).

   o  For all other tunneling protocols (GRE, GREIPv4, IPv4INIPv4,
      MINENC, IPv6INIPv4), the tunnel entry-point inserts an additional
      UDP header between the tunnel header and the original packet.  The
      Flow ID consists of the tunnel entry-point and tunnel exit-point
      IP addresses and the source port number in the additional UDP
      header.  The source port number is dynamically chosen by the
      tunnel entry-point and conveyed to the tunnel exit-point.  In
      these cases, it is especially important that the tunnel exit-point
      understands the additional UDP encapsulation, and therefore can
      correctly decapsulate both the normal tunnel header and the
      additional UDP header.  In other words, both tunnel endpoints need
      to be NSIS-tunnel-aware.




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   The above recommendations about choosing the tunnel Flow ID apply to
   dynamically created QoS tunnel sessions.  For preconfigured QoS
   tunnel sessions, the corresponding Flow ID is determined by the
   configuration mechanism itself.  For example, if the tunnel QoS is
   Diffserv based, the Diffserv Code Point (DSCP) field value may be
   used to identify the corresponding tunnel session.

5.  NSIS Operation over Tunnels with Preconfigured QoS Sessions

   When tunnel QoS is managed by preconfigured QoS sessions, both the
   tunnel entry-point and tunnel exit-point need to be configured with
   information about the Flow ID of the tunnel QoS session.  This allows
   the tunnel endpoints to correctly perform matching encapsulating and
   decapsulating operations.  The procedures of NSIS operating over
   tunnels with preconfigured QoS sessions depend on whether the end-to-
   end NSIS signaling is sender-initiated or receiver-initiated.  But in
   both cases, it is the tunnel entry-point that first creates the
   mapping between a tunnel session and an end-to-end session.

5.1.  Sender-initiated Reservation

   Figure 6 illustrates the signaling sequence when end-to-end signaling
   outside the tunnel is sender-initiated.  Upon receiving a RESERVE
   message from the sender, Tentry checks the tunnel QoS configuration,
   determines whether and how this end-to-end session can be mapped to a
   preconfigured tunnel session.  The mapping criteria are part of the
   preconfiguration and outside the scope of this document.  Tentry then
   tunnels the RESERVE message to Texit.  Texit forwards the RESERVE
   message to the receiver.  The receiver replies with a RESPONSE
   message that arrives at Texit, Tentry, and finally the sender.  If
   the RESPONSE message that Tentry receives confirms that the overall
   signaling is successful, Tentry starts to encapsulate all incoming
   packets of the data flow using the tunnel Flow ID corresponding to
   the mapped tunnel session.  Texit knows how to decapsulate the tunnel
   packets because it recognizes the mapped tunnel Flow ID based on
   information supplied during tunnel session preconfiguration.















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    Sender         Tentry          Tmid          Texit         Receiver

      |              |              |              |              |
      |   RESERVE    |              |              |              |
      +------------->|              |              |              |
      |              |           RESERVE           |              |
      |              +---------------------------->|              |
      |              |              |              |   RESERVE    |
      |              |              |              +------------->|
      |              |              |              |   RESPONSE   |
      |              |              |              |<-------------+
      |              |           RESPONSE          |              |
      |              |<----------------------------+              |
      |   RESPONSE   |              |              |              |
      |<-------------+              |              |              |
      |              |              |              |              |
      |              |              |              |              |

     Figure 6: Sender-Initiated End-to-End Session with Preconfigured
                            Tunnel QoS Sessions

5.2.  Receiver-Initiated Reservation

   Figure 7 shows the signaling sequence when end-to-end signaling
   outside the tunnel is receiver-initiated.  Upon receiving the first
   end-to-end Query message, Tentry examines the tunnel QoS
   configuration, then updates and tunnels the Query message to Texit.
   Texit decapsulates the QUERY message, processes it, and forwards it
   toward the receiver.  The receiver sends back a RESERVE message
   passing through Texit and arriving at Tentry.  Tentry decides on
   whether and how the QoS request for this end-to-end session can be
   mapped to a preconfigured tunnel session based on criteria outside
   the scope of this document.  Then, Tentry forwards the RESERVE
   message towards the sender.  The signaling continues until a RESPONSE
   message arrives at Tentry, Texit, and finally the receiver.  If the
   RESPONSE message that Tentry receives confirms that the overall
   signaling is successful, Tentry starts to encapsulate all incoming
   packets of the data flow using the tunnel Flow ID corresponding to
   the mapped tunnel session.  Similarly, Texit knows how to decapsulate
   the tunnel packets because it recognizes the mapped tunnel Flow ID
   based on information supplied during tunnel session preconfiguration.

   Since separate tunnel QoS signaling is not involved in preconfigured
   QoS tunnels, Figures 6 and 7 make the tunnel look like a single
   virtual link.  The signaling path simply skips all tunnel
   intermediate nodes.  However, both Tentry and Texit need to deploy
   the NSIS-tunnel-related functionalities described above, including
   acting on the end-to-end NSIS signaling messages based on tunnel QoS



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   status, mapping end-to-end and tunnel QoS sessions, and correctly
   encapsulating and decapsulating tunnel packets according to the
   tunnel protocol and the configured tunnel Flow ID.

    Sender         Tentry          Tmid          Texit         Receiver

      |              |              |              |              |
      |    QUERY     |              |              |              |
      +------------->|              |              |              |
      |              |            QUERY            |              |
      |              +---------------------------->|              |
      |              |              |              |    QUERY     |
      |              |              |              +------------->|
      |              |              |              |   RESERVE    |
      |              |              |              |<-------------+
      |              |           RESERVE           |              |
      |              |<----------------------------+              |
      |   RESERVE    |              |              |              |
      |<-------------+              |              |              |
      |   RESPONSE   |              |              |              |
      +------------->|              |              |              |
      |              |           RESPONSE          |              |
      |              +---------------------------->|              |
      |              |              |              |   RESPONSE   |
      |              |              |              +------------->|
      |              |              |              |              |
      |              |              |              |              |

    Figure 7: Receiver-Initiated End-to-End Session with Preconfigured
                            Tunnel QoS Sessions

6.  NSIS Operation over Tunnels with Dynamically Created QoS Sessions

   When there are no preconfigured tunnel QoS sessions, a tunnel can
   apply the same NSIS QoS signaling mechanism used for the end-to-end
   path to manage the QoS inside the tunnel.  The tunnel NSIS signaling
   involves only those NSIS nodes in the tunnel forwarding path.  The
   Flow IDs for the tunnel signaling are based on tunnel header fields.
   NSIS peer discovery messages inside the tunnel distinguish themselves
   using the tunnel header fields, which solves the problem for tunnel
   intermediate NSIS nodes to intercept signaling messages.

   When tunnel endpoints dynamically create tunnel QoS sessions, the
   initiation mode of the tunnel session always follows the initiation
   mode of the end-to-end session.  Specifically, when the end-to-end
   session is sender-initiated, the tunnel session should also be
   sender-initiated; when the end-to-end session is receiver-initiated,
   the tunnel session should also be receiver-initiated.



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   The tunnel entry-point conveys the corresponding tunnel Flow ID
   associated with an end-to-end session to the tunnel exit-point during
   the tunnel signaling process.  The tunnel entry-point also informs
   the exit-point of the binding between the corresponding tunnel
   session and end-to-end session through the BOUND_SESSION_ID QoS NSLP
   message object.  The reservation message dependencies between the
   tunnel session and end-to-end session are resolved using the MSG-ID
   and BOUND-MSG-ID objects of the QoS NSLP message binding mechanism.

6.1.  Sender-Initiated Reservation

   Figure 8 shows the typical messaging sequence of how NSIS operates
   over IP tunnels when both the end-to-end session and tunnel session
   are sender-initiated.  Tunnel signaling messages are distinguished
   from end-to-end messages by a prime symbol after the message name.
   The sender first sends an end-to-end RESERVE message (1) that arrives
   at Tentry.  Tentry chooses the tunnel Flow ID, creates the tunnel
   session, and associates the end-to-end session with the tunnel
   session.  Tentry then sends a tunnel RESERVE' message (2) matching
   the request of the end-to-end session towards Texit to reserve tunnel
   resources.  This RESERVE' message (2) includes a MSG-ID object that
   contains a randomly generated 128-bit MSG-ID.  Meanwhile, Tentry
   inserts a BOUND-MSG-ID object containing the same MSG-ID as well as a
   BOUND-SESSION-ID object containing the SESSION-ID of the tunnel
   session into the original RESERVE message, and sends this RESERVE
   message (3) towards Texit using normal tunnel encapsulation.  The
   Message_Binding_Type flags of both the MSG-ID and BOUND-MSG-ID
   objects in the RESERVE' and RESERVE messages (2, 3) are SET,
   indicating a bidirectional binding.  The tunnel RESERVE' message (2)
   is processed hop-by-hop inside the tunnel for the flow identified by
   the chosen tunnel Flow ID, while the end-to-end RESERVE message (3)
   passes through the tunnel intermediate nodes (Tmid) just like other
   tunneled packets.  These two messages could arrive at Texit in
   different orders, and the reaction of Texit in these different
   situations should combine the tunnel QoS message processing rules
   with the QoS NSLP processing principles for message binding
   [RFC5974], as illustrated below.

   The first possibility is shown in the example messaging flow of
   Figure 8, where the tunnel RESERVE' message (2), also known as the
   triggering message in QoS NSLP message binding terms, arrives first.
   Since the message binding is bidirectional, Texit records the MSG-ID
   of the RESERVE' message (2), enqueues it and starts a MsgIDWait timer
   waiting for the end-to-end RESERVE message (3), also known as the
   bound signaling message in QoS NSLP message binding terms.  The timer






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   Sender         Tentry         Tmid           Texit         Receiver

     |              |              |              |              |
     | RESERVE(1)   |              |              |              |
     +------------->|              |              |              |
     |              | RESERVE'(2)  |              |              |
     |              +=============>|              |              |
     |              |              | RESERVE'(2)  |              |
     |              |              +=============>|              |
     |              |          RESERVE(3)         |              |
     |              +---------------------------->|              |
     |              |              | RESPONSE'(4) |              |
     |              |              |<=============+              |
     |              | RESPONSE'(4) |              |              |
     |              |<=============+              |              |
     |              |              |              |  RESERVE(5)  |
     |              |              |              +------------->|
     |              |              |              | RESPONSE(6)  |
     |              |              |              |<-------------+
     |              |         RESPONSE(6)         |              |
     |              |<----------------------------+              |
     | RESPONSE(6)  |              |              |              |
     |<-------------+              |              |              |
     |              |              |              |              |
     |              |              |              |              |

     (1,5): RESERVE w/o BOUND-MSG-ID and BOUND-SESSION-ID
     (2): RESERVE' w/ MSG-ID
     (3): RESERVE w/ BOUND-MSG-ID and BOUND-SESSION-ID

   Figure 8: Sender-Initiated Reservation for Both End-to-End and Tunnel
                                 Signaling

   value is set to the default retransmission timeout period
   QOSNSLP_REQUEST_RETRY.  When the end-to-end RESERVE message (3)
   arrives, Texit notices that there is an existing stored MSG-ID which
   matches the MSG-ID in the BOUND-MSG-ID object of the incoming RESERVE
   message (3).  Therefore, the message binding condition has been
   satisfied.  Texit resumes processing of the tunnel RESERVE' message
   (2), creates the reservation state for the tunnel session, and sends
   a tunnel RESPONSE' message (4) to Tentry.  At the same time, Texit
   checks the BOUND-SESSION-ID object of the end-to-end RESERVE message
   (3) and records the binding of the corresponding tunnel session with
   the end-to-end session.  Texit also updates the end-to-end RESERVE
   message based on the result of the tunnel session reservation,
   removes its tunnel BOUND-SESSION-ID and BOUND-MSG-ID object and
   forwards the end-to-end RESERVE message (5) along the path towards




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   the receiver.  When the receiver receives the end-to-end RESERVE
   message (5), it sends an end-to-end RESPONSE message (6) back to the
   sender.

   The second possibility is that the end-to-end RESERVE message arrives
   before the tunnel RESERVE' message at Texit.  In that case, Texit
   notices a BOUND-SESSION-ID object and a BOUND-MSG-ID object in the
   end-to-end RESERVE message, but realizes that the tunnel session does
   not exist yet.  So, Texit enqueues the RESERVE message and starts a
   MsgIDWait timer.  The timer value is set to the default
   retransmission timeout period QOSNSLP_REQUEST_RETRY.  When the
   corresponding tunnel RESERVE' message arrives with a MSG-ID matching
   that of the outstanding BOUND-MSG-ID object, the message binding
   condition is satisfied.  Texit sends a tunnel RESPONSE' message back
   to Tentry and updates the end-to-end RESERVE message by incorporating
   the result of the tunnel session reservation, as well as removing the
   tunnel BOUND-SESSION-ID and BOUND-MSG-ID objects.  Texit then
   forwards the end-to-end RESERVE message along the path towards the
   receiver.  When the receiver receives the end-to-end RESERVE message,
   it sends an end-to-end RESPONSE message back to the sender.

   Yet another possibility is that the tunnel RESERVE' message arrives
   at Texit first, but the end-to-end RESERVE message never arrives.  In
   that case, the MsgIDWait timer for the queued tunnel RESERVE' message
   will expire.  Texit should then send a tunnel RESPONSE' message back
   to Tentry indicating a reservation error has occurred, and discard
   the tunnel RESERVE' message.  The last possibility is that the end-
   to-end RESERVE message arrives at Texit first, but the tunnel
   RESERVE' message never arrives.  In that case, the MsgIDWait timer
   for the queued end-to-end RESERVE message will expire.  Texit should
   then treat this situation as a local reservation failure, and
   according to [RFC5974], Texit as a stateful QoS NSLP should generate
   an end-to-end RESPONSE message indicating RESERVE error to the
   sender.

   Once the end-to-end and the tunnel QoS session have both been
   successfully created and associated, the tunnel endpoints Tentry and
   Texit coordinate the signaling between the two sessions and make sure
   that adjustment or teardown of either session may trigger similar
   actions for the other session as necessary, by invoking appropriate
   signaling messages.

6.2.  Receiver-Initiated Reservation

   Figure 9 shows the typical messaging sequence of how NSIS signaling
   operates over IP tunnels when both end-to-end and tunnel sessions are
   receiver-initiated.  Upon receiving an end-to-end QUERY message (1)
   from the sender, Tentry chooses the tunnel Flow ID and sends a tunnel



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   Sender         Tentry          Tmid          Texit         Receiver

     |              |              |              |              |
     |   QUERY(1)   |              |              |              |
     +------------->|              |              |              |
     |              |  QUERY'(2)   |              |              |
     |              +=============>|              |              |
     |              |              |  QUERY'(2)   |              |
     |              |              +=============>|              |
     |              |              | RESPONSE'(3) |              |
     |              |              |<=============+              |
     |              | RESPONSE'(3) |              |              |
     |              |<=============+              |              |
     |              |           QUERY(4)          |              |
     |              +---------------------------->|              |
     |              |              |              |   QUERY(5)   |
     |              |              |              +------------->|
     |              |              |              |  RESERVE(6)  |
     |              |              |              |<-------------+
     |              |              | RESERVE'(7)  |              |
     |              |              |<=============+              |
     |              | RESERVE'(7)  |              |              |
     |              |<=============+              |              |
     |              |          RESERVE(8)         |              |
     |              |<----------------------------+              |
     |              | RESPONSE'(9) |              |              |
     |              +=============>|              |              |
     |              |              | RESPONSE'(9) |              |
     |              |              +=============>|              |
     | RESERVE(10)  |              |              |              |
     |<-------------+              |              |              |
     | RESPONSE(11) |              |              |              |
     +------------->|              |              |              |
     |              |         RESPONSE(11)        |              |
     |              +---------------------------->|              |
     |              |              |              | RESPONSE(11) |
     |              |              |              +------------->|
     |              |              |              |              |
     |              |              |              |              |
     (1), (5): QUERY w/ RESERVE-INIT
     (2): QUERY' w/ RII
     (4): QUERY w/ RESERVE-INIT and BOUND-SESSION-ID
     (6), (10): RESERVE w/o BOUND-SESSION-ID
     (7): RESERVE' w/ MSG-ID
     (8): RESERVE w/ BOUND-MSG-ID and BOUND-SESSION-ID

     Figure 9: Receiver-Initiated Reservation for Both End-to-end and
                             Tunnel Signaling



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   QUERY' message (2) matching the request of the end-to-end session
   towards Texit.  This tunnel QUERY' message (2) is meant to discover
   QoS characteristics of the tunnel path, rather than initiate an
   actual reservation.  Therefore, it includes a Request Identification
   Information (RII) object but does not set the RESERVE-INIT flag.  The
   tunnel QUERY' message (2) is processed hop-by-hop inside the tunnel
   for the flow identified by the tunnel Flow ID.  When Texit receives
   this tunnel QUERY' message (2), it replies with a corresponding
   tunnel RESPONSE' message (3) containing the tunnel path
   characteristics.  After receiving the tunnel RESPONSE' message (3),
   Tentry creates the tunnel session, generates an outgoing end-to-end
   QUERY message (4) considering the tunnel path characteristics,
   appends a tunnel BOUND-SESSION-ID object containing the tunnel
   SESSION-ID, and sends it toward Texit using normal tunnel
   encapsulation.  The end-to-end QUERY message (4) passes along tunnel
   intermediate nodes like other tunneled packets.  Upon receiving this
   end-to-end QUERY message (4), Texit notices the tunnel session
   binding, creates the tunnel session state, removes the tunnel BOUND-
   SESSION-ID object, and forwards the end-to-end QUERY message (5)
   further along the path.

   The end-to-end QUERY message (5) arrives at the receiver and triggers
   a RESERVE message (6).  When Texit receives the RESERVE message (6),
   it notices that the session is bound to a receiver-initiated tunnel
   session.  Therefore, Texit triggers a RESERVE' message (7) toward
   Tentry for the tunnel session reservation.  This tunnel RESERVE'
   message (7) includes a randomly generated 128-bit MSG-ID.  Meanwhile,
   Texit inserts a BOUND-MSG-ID object containing the same MSG-ID and a
   BOUND-SESSION-ID object containing the tunnel SESSION-ID into the
   end-to-end RESERVE message (8), and sends it towards Tentry using
   normal tunnel encapsulation.  The Message_Binding_Type flags of the
   MSG-ID and BOUND-MSG-ID objects in the RESERVE' and RESERVE messages
   (7,8) are SET, indicating a bidirectional binding.

   At Tentry, the tunnel RESERVE' message (7) and the end-to-end RESERVE
   message (8) could arrive in either order.  In a typical case shown in
   Figure 9, the tunnel RESERVE' message (7) arrives first.  Tentry then
   records the MSG-ID of the tunnel RESERVE' message (7) and starts a
   MsgIDWait timer.  When the end-to-end RESERVE message (8) with the
   BOUND-MSG-ID object containing the same MSG-ID arrives, the message
   binding condition is satisfied.  Tentry resumes processing of the
   tunnel RESERVE' message (7), creates the reservation state for the
   tunnel session, and sends a tunnel RESPONSE' message (9) to Texit.
   At the same time, Tentry creates the outgoing end-to-end RESERVE
   message (10) by incorporating results of the tunnel session
   reservation and removing the BOUND-SESSION-ID and BOUND-MSG-ID





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   objects, and forwards it along the path towards the sender.  When the
   sender receives the end-to-end RESERVE message (10), it sends an end-
   to-end RESPONSE message (11) back to the receiver.

   If the end-to-end RESERVE message arrives before the tunnel RESERVE'
   message at Tentry, or either of the two messages fails to arrive at
   Tentry, the processing rules at Tentry are similar to those of Texit
   in the situation discussed in Section 6.1.

   Once the end-to-end and the tunnel QoS session have both been
   successfully created and associated, the tunnel endpoints Tentry and
   Texit coordinate the signaling between the two sessions and make sure
   that adjustment or teardown of either session can trigger similar
   actions for the other session as necessary, by invoking appropriate
   signaling messages.

7.  NSIS-Tunnel Signaling Capability Discovery

   The mechanism of NSIS operating over IP tunnels requires the
   coordination of both tunnel endpoints in tasks such as special
   encapsulation and decapsulation of data flow packets according to the
   chosen tunnel Flow ID, as well as the possible creation and
   adjustment of the end-to-end and tunnel QoS sessions.  Therefore, one
   NSIS-tunnel-aware endpoint needs to know that the other tunnel
   endpoint is also NSIS-tunnel-aware before initiating this mechanism
   of NSIS operating over IP tunnels.  In some cases, especially for IP
   tunnels with preconfigured QoS sessions, an NSIS-tunnel-aware
   endpoint can learn about whether the other tunnel endpoint is also
   NSIS-tunnel-aware through preconfiguration.  In other cases where
   such preconfiguration is not available, the initiating NSIS-tunnel-
   aware endpoint may dynamically discover the other tunnel endpoint's
   capability through a QoS NSLP NODE_CAPABILITY_TUNNEL object defined
   in this section.

   The NODE_CAPABILITY_TUNNEL object is a zero-length object with a
   standard NSLP object header as shown in Figure 10.

     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |A|B|r|r|         Type          |r|r|r|r|        Length         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 10: NODE_CAPABILITY_TUNNEL Object Format

   Type: NODE_CAPABILITY_TUNNEL (0x015) from the shared NSLP object type
   space




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   Length: 0

   The bits marked 'A' and 'B' define the desired behavior for objects
   whose Type field is not recognized.  If a node does not recognize the
   NODE_CAPABILITY_TUNNEL object, the desired behavior is "Forward".
   That is, the object must be retained unchanged and forwarded as a
   result of message processing.  This is satisfied by setting 'AB' to
   '10'.

   The 'r' bit stands for 'reserved'.

   The NODE_CAPABILITY_TUNNEL object is included in a tunnel QUERY' or
   RESERVE' message by a tunnel endpoint that needs to learn about the
   other endpoint's capability for NSIS tunnel handling.  If the
   receiving tunnel endpoint is indeed NSIS-tunnel-aware, it recognizes
   this object and knows that the sending endpoint is NSIS-tunnel-aware.
   The receiving tunnel endpoint places the same object in a tunnel
   RESPONSE' message to inform the sending endpoint that it is also
   NSIS-tunnel-aware.  The use of the NODE_CAPABILITY_TUNNEL object in
   the cases of sender-initiated reservation and receiver-initiated
   reservation are as follows.

   First, assume that the end-to-end session is sender-initiated as in
   Figure 8, and the NSIS-tunnel-aware Tentry wants to discover the NSIS
   tunnel capability of Texit.  After receiving the first end-to-end
   RESERVE message (1), Tentry inserts an RII object and a
   NODE_CAPABILITY_TUNNEL object into the tunnel RESERVE' message (2)
   and sends it to Texit.  If Texit is NSIS-tunnel-aware, it learns from
   the NODE_CAPABILITY_TUNNEL object that Tentry is also NSIS-tunnel-
   aware and includes the same object into the tunnel RESPONSE' message
   (4) sent back to Tentry.

   Second, assume that the end-to-end session is receiver-initiated as
   in Figure 9, and the NSIS-tunnel-aware Tentry wants to discover the
   NSIS tunnel capability of Texit.  Upon receiving the first end-to-end
   QUERY message (1), Tentry inserts an RII object and a
   NODE_CAPABILITY_TUNNEL object in the tunnel QUERY' message (2) and
   sends it toward Texit.  If Texit is NSIS-tunnel-aware, it learns from
   the NODE_CAPABILITY_TUNNEL object that Tentry is also NSIS-tunnel-
   aware and includes the same object tunnel RESPONSE' message (3) sent
   to Tentry.

8.  IANA Considerations

   This document defines a new object type called NODE_CAPABILITY_TUNNEL
   for QoS NSLP.  Its Type value (0x015) has been assigned by IANA.  The
   object format and the setting of the extensibility bits are defined
   in Section 7.



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9.  Security Considerations

   This NSIS and IP tunnel interoperation mechanism has two IPsec-
   related security implications.  First, NSIS messages may require per-
   hop processing within the IPsec tunnel, and that is potentially
   incompatible with IPsec.  A similar problem exists for RSVP
   interacting with IPsec, when the Router Alert option is used
   (Appendix A.1 of RFC 4302 [RFC4302]).  If this mechanism is indeed
   used for NSIS and IPsec tunnels, a so-called covert channel could
   exist where someone can create spurious NSIS signaling flows within
   the protected network in order to create signaling in the outside
   network, which then someone else is monitoring.  For highly secure
   networks, this would be seen as a way to smuggle information out of
   the network, and therefore this channel will need to be rate-limited.
   A similar covert channel rate-limit problem exists for using
   Differentiated Services (DS) or Explicit Congestion Notification
   (ECN) fields with IPsec (Section 5.1.2 of RFC 4301 [RFC4301]).

   Second, since the NSIS-tunnel-aware endpoint is responsible for
   adapting changes between the NSIS signaling both inside and outside
   the tunnel, there could be additional risks for an IPsec endpoint
   that is also an NSIS-tunnel-aware endpoint.  For example, security
   vulnerability (e.g., buffer overflow) on the NSIS stack of that IPsec
   tunnel endpoint may be exposed to the unprotected outside network.
   Nevertheless, it should also be noted that if any node along the
   signaling path is compromised, the whole end-to-end QoS signaling
   could be affected, whether or not the end-to-end path includes an
   IPsec tunnel.

   Several other documents discuss security issues for NSIS.  General
   threats for NSIS can be found in [RFC4081].  Security considerations
   for NSIS NTLP and QoS NSLP are discussed in [RFC5971] and [RFC5974],
   respectively.

10.  Acknowledgments

   The authors would like to thank Roland Bless, Francis Dupont, Lars
   Eggert, Adrian Farrel, Russ Housley, Georgios Karagiannis, Jukka
   Manner, Martin Rohricht, Peter Saint-Andre, Martin Stiemerling,
   Hannes Tschofenig, and other members of the NSIS working group for
   comments.  Thanks to Yaron Sheffer for pointing out the IPsec-related
   security considerations.









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11.  References

11.1.  Normative References

   [RFC2113]  Katz, D., "IP Router Alert Option", RFC 2113,
              February 1997.

   [RFC2473]  Conta, A. and S. Deering, "Generic Packet Tunneling in
              IPv6 Specification", RFC 2473, December 1998.

   [RFC2711]  Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
              RFC 2711, October 1999.

   [RFC2746]  Terzis, A., Krawczyk, J., Wroclawski, J., and L. Zhang,
              "RSVP Operation Over IP Tunnels", RFC 2746, January 2000.

   [RFC3697]  Rajahalme, J., Conta, A., Carpenter, B., and S. Deering,
              "IPv6 Flow Label Specification", RFC 3697, March 2004.

   [RFC4080]  Hancock, R., Karagiannis, G., Loughney, J., and S. Van den
              Bosch, "Next Steps in Signaling (NSIS): Framework",
              RFC 4080, June 2005.

   [RFC4081]  Tschofenig, H. and D. Kroeselberg, "Security Threats for
              Next Steps in Signaling (NSIS)", RFC 4081, June 2005.

   [RFC5971]  Schulzrinne, H. and R. Hancock, "GIST: General Internet
              Signalling Transport", RFC 5971, October 2010.

   [RFC5974]  Manner, J., Karagiannis, G., and A. McDonald, "NSIS
              Signaling Layer Protocol (NSLP) for Quality-of-Service
              Signaling", RFC 5974, October 2010.

11.2.  Informative References

   [RFC1701]  Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic
              Routing Encapsulation (GRE)", RFC 1701, October 1994.

   [RFC1702]  Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic
              Routing Encapsulation over IPv4 networks", RFC 1702,
              October 1994.

   [RFC1853]  Simpson, W., "IP in IP Tunneling", RFC 1853, October 1995.

   [RFC2003]  Perkins, C., "IP Encapsulation within IP", RFC 2003,
              October 1996.





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   [RFC2004]  Perkins, C., "Minimal Encapsulation within IP", RFC 2004,
              October 1996.

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
              Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1
              Functional Specification", RFC 2205, September 1997.

   [RFC2784]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
              Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
              March 2000.

   [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
              for IPv6 Hosts and Routers", RFC 4213, October 2005.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              December 2005.

   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, December 2005.

   [RFC5944]  Perkins, C., Ed., "IP Mobility Support for IPv4, Revised",
              RFC 5944, November 2010.


























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Authors' Addresses

   Charles Shen
   Columbia University
   Department of Computer Science
   1214 Amsterdam Avenue, MC 0401
   New York, NY  10027
   USA

   Phone: +1 212 854 3109
   EMail: charles@cs.columbia.edu


   Henning Schulzrinne
   Columbia University
   Department of Computer Science
   1214 Amsterdam Avenue, MC 0401
   New York, NY  10027
   USA

   Phone: +1 212 939 7004
   EMail: hgs@cs.columbia.edu


   Sung-Hyuck Lee
   Convergence Technologies & Standardization Lab
   Samsung Information System America, INC.
   95 West Plumeria Drive
   San Jose, CA  95134
   USA

   Phone: 1-408-544-5809
   EMail: sung1.lee@samsung.com


   Jong Ho Bang
   SAMSUNG Advanced Institute of Technology
   San 14-1, Nongseo-ri, Giheung-eup
   Yongin-si, Gyeonggi-do  449-712
   South Korea

   Phone: +82 31 280 9585
   EMail: jh0278.bang@samsung.com








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