Non-Penultimate Hop Popping Behavior and Out-of-Band Mapping for RSVP-TE Label Switched Paths
RFC 6511

Internet Engineering Task Force (IETF)                            Z. Ali
Request for Comments: 6511                                    G. Swallow
Category: Standards Track                                  Cisco Systems
ISSN: 2070-1721                                              R. Aggarwal
                                                        Juniper Networks
                                                           February 2012

    Non-Penultimate Hop Popping Behavior and Out-of-Band Mapping for
                      RSVP-TE Label Switched Paths

Abstract

   There are many deployment scenarios that require an egress Label
   Switching Router (LSR) to receive binding of the Resource Reservation
   Protocol - Traffic Engineering (RSVP-TE) Label Switched Path (LSP) to
   an application and a payload identifier using some "out-of-band"
   (OOB) mechanism.  This document defines protocol mechanisms to
   address this requirement.  The procedures described in this document
   are equally applicable for point-to-point (P2P) and point-to-
   multipoint (P2MP) LSPs.

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 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/rfc6511.

Copyright Notice

   Copyright (c) 2012 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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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect

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   to this document.  Code Components extracted from this document must
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   the Trust Legal Provisions and are provided without warranty as
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   This document may contain material from IETF Documents or IETF
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   than English.

 Table of Contents

   1. Introduction ....................................................2
      1.1. Conventions Used in This Document ..........................3
   2. RSVP-TE Signaling Extensions ....................................3
      2.1. Signaling Non-PHP Behavior .................................3
      2.2. Signaling OOB Mapping Indication ...........................5
      2.3. Relationship between OOB and Non-PHP Flags .................6
      2.4. Egress Procedure for Label Binding .........................6
   3. Security Considerations .........................................7
   4. IANA Considerations .............................................7
      4.1. Attribute Flags for LSP Attributes Object ..................7
      4.2. New RSVP Error Sub-Code ....................................8
   5. Acknowledgements ................................................8
   6. References ......................................................8
      6.1. Normative References .......................................8
      6.2. Informative References .....................................9

1.  Introduction

   When Resource Reservation Protocol - Traffic Engineering (RSVP-TE) is
   used for applications like Multicast Virtual Private Network (MVPN)
   [RFC6513] and Virtual Private LAN Service (VPLS) [RFC4761], an egress
   Label Switching Router (LSR) receives the binding of the RSVP-TE
   Label Switched Path (LSP) to an application and a payload identifier
   using an "out-of-band" (OOB) mechanism (e.g., Border Gateway Protocol
   (BGP)).  In such cases, the egress LSR cannot make correct forwarding
   decisions until such OOB mapping information is received.
   Furthermore, in order to apply the binding information, the egress
   LSR needs to identify the incoming LSP on which traffic is coming.

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   Therefore, non-Penultimate Hop Popping (non-PHP) behavior is required
   to apply OOB mapping.  Non-PHP behavior requires the egress LSRs to
   assign a non-NULL label for the LSP being signaled.

   There are other applications that require non-PHP behavior.  When
   RSVP-TE point-to-multipoint (P2MP) LSPs are used to carry IP
   multicast traffic non-PHP behavior enables a leaf LSR to identify the
   P2MP TE LSP on which traffic is received.  Hence, the egress LSR can
   determine whether traffic is received on the expected P2MP LSP and
   discard traffic that is not received on the expected P2MP LSP.  Non-
   PHP behavior is also required to determine the context of upstream
   assigned labels when the context is a MPLS LSP.  Non-PHP behavior may
   also be required for MPLS Transport Profile (MPLS-TP) LSPs [RFC5921].

   This document defines two new flags in the Attributes Flags TLV of
   the LSP Attributes object defined in [RFC5420]: one flag for
   communication of non-PHP behavior and one flag to indicate that the
   binding of the LSP to an application and a payload identifier
   (Payload ID) needs to be learned via an out-of-band mapping
   mechanism.  As there is one-to-one correspondence between bits in the
   Attribute Flags TLV and the Record Route Object (RRO) Attributes
   subobject, corresponding flags to be carried in the RRO Attributes
   subobject are also defined.

   The procedures described in this document are equally applicable for
   point-to-point (P2P) and P2MP LSPs.  Specification of the OOB
   communication mechanism(s) is beyond the scope of this document.

1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  RSVP-TE Signaling Extensions

   This section describes the signaling extensions required to address
   the above-mentioned requirements.

2.1.  Signaling Non-PHP Behavior

   In order to request non-PHP behavior for an RSVP-TE LSP, this
   document defines a new flag in the Attributes Flags TLV of the LSP
   Attributes object defined in [RFC5420]:

      Bit Number 7: Non-PHP behavior flag

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   In order to indicate to the ingress LSR that the egress LSR
   recognizes the "Non-PHP behavior flag", the same bit is used in the
   Flags field of the Record Route Object (RRO) Attributes subobject.

   An ingress LSR sets the "Non-PHP behavior flag" to signal that the
   egress LSRs SHOULD assign a non-NULL label for the LSP being
   signaled.  This flag MUST NOT be modified by any other LSRs in the
   network.  LSRs other than the egress LSRs SHOULD ignore this flag.

   If an egress LSR receiving the Path message supports the LSP
   Attributes object and the Attributes Flags TLV and also recognizes
   the "Non-PHP behavior flag", it MUST allocate a non-NULL local label.
   The egress LSR MUST also set the "Non-PHP behavior flag" in the Flags
   field of the RRO Attributes subobject.

   If the egress LSR

   -  supports the LSP Attributes object but does not recognize the
      Attributes Flags TLV; or

   -  supports the LSP Attributes object and recognizes the Attributes
      Flags TLV, but does not recognize the "Non-PHP behavior flag";

   then it silently ignores the request according to the processing
   rules of [RFC5420].

   An ingress LSR requesting non-PHP behavior SHOULD examine the "Non-
   PHP behavior flag" in the Flags field of the RRO Attributes subobject
   and MAY send a Path Tear to the egress, which has not set the "Non-
   PHP behavior flag".  An ingress LSR requesting non-PHP behavior MAY
   also examine the label value corresponding to the egress LSR(s) in
   the RRO and MAY send a Path Tear to the egress, which assigns a NULL
   label value.

   When signaling a P2MP LSP, a source node may wish to solicit an
   individual response to the "Non-PHP behavior flag" from the leaf
   nodes.  Given the constraints on how the LSP Attributes may be
   carried in Path and Resv messages according to [RFC5420], in this
   situation, the source node MUST use a separate Path message for each
   leaf in networks where [RFC6510] is not supported.  In networks with
   [RFC6510] deployed, either a single leaf per Path message or multiple
   leaves per Path message MAY be used by the source node.

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2.2.  Signaling OOB Mapping Indication

   This document defines a single flag to indicate that the normal
   binding mechanism of an RSVP session is overridden.  The actual out-
   of-band mappings are beyond the scope of this document.  The flag is
   carried in the Attributes Flags TLV of the LSP Attributes object
   defined in [RFC5420] and is defined as follows:

      Bit Number 8: OOB mapping flag

   In order to indicate to the ingress LSR that the egress LSR
   recognizes the "OOB mapping flag", the following same bit is used in
   the Flags field of the Record Route object (RRO) Attributes
   subobject.

   An ingress LSR sets the "OOB mapping flag" to signal the egress LSR
   that the binding of RSVP-TE LSP to an application and a payload
   identifier is being signaled out-of-band.  This flag MUST NOT be
   modified by any other LSRs in the network.  LSRs other than the
   egress LSRs SHOULD ignore this flag.

   When an egress LSR that supports the "OOB mapping flag" receives a
   Path message with that flag set, the egress LSR  MUST set the "OOB
   mapping flag" in the Flags field of the RRO Attributes subobject.
   The rest of the RSVP signaling proceeds as normal.  However, the LSR
   MUST have received the OOB mapping before accepting traffic on the
   LSP.  This implies that the egress LSR MUST NOT set up forwarding
   state for the LSP before it receives the OOB mapping.

   Note that the payload information SHOULD be supplied by the OOB
   mapping.  If the egress LSR receives the payload information from OOB
   mapping, then the LSR MUST ignore the L3PID (Layer 3 Protocol ID) in
   the Label Request Object [RFC3209].

   If the egress LSR

   -  supports the LSP Attributes object but does not recognize the
      Attributes Flags TLV; or

   -  supports the LSP Attributes object and recognizes the Attributes
      Flags TLV, but does not recognize the "OOB mapping flag";

   then it silently ignores the request according to the processing
   rules of [RFC5420].

   An ingress LSR requesting OOB mapping SHOULD examine the "OOB mapping
   flag" in the Flags field of the RRO Attributes subobject and MAY send
   a Path Tear to the egress, which has not set the "OOB mapping flag".

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   When signaling a P2MP LSP, a source node may wish to solicit an
   individual response to the "OOB mapping flag" from the leaf nodes.
   Given the constraints on how the LSP Attributes object may be carried
   in Path and Resv messages according to [RFC5420], in this situation,
   the source node MUST use a separate Path message for each leaf in
   networks where [RFC6510] is not supported.  In networks with
   [RFC6510] deployed, either a single leaf per Path message or multiple
   leaves per Path message MAY be used by the source node.

   In deploying applications where the egress LSR receives the binding
   of the RSVP-TE LSP to an application and a payload identifier using
   an OOB mechanism, it is important to recognize that the OOB mapping
   is sent asynchronously with respect to the signaling of RSVP-TE LSP.
   The egress LSR only installs forwarding state for the LSP after it
   receives the OOB mapping.  In deploying applications using an OOB
   mechanism, an ingress LSR may need to know when the egress is
   properly set up for forwarding (i.e., has received the OOB mapping).
   How the ingress LSR determines that the LSR is properly set up for
   forwarding at the egress LSR is beyond the scope of this document.
   Nonetheless, if the OOB mapping is not received by the egress LSR
   within a reasonable time, the procedure defined in Section 2.4 to
   tear down the LSP is followed.

2.3.  Relationship between OOB and Non-PHP Flags

   The "Non-PHP behavior flag" and "OOB mapping flag" can appear and be
   processed independently of each other.  However, as mentioned
   earlier, in the context of the applications discussed in this
   document, OOB mapping requires non-PHP behavior.  An ingress LSR
   requesting the OOB mapping MAY also set the "Non-PHP behavior flag"
   in the LSP Attributes object in the Path message.

2.4.  Egress Procedure for Label Binding

   RSVP-TE signaling completion and the OOB mapping information
   reception happen asynchronously at the egress.  As mentioned in
   Section 2.2, egress waits for the OOB mapping before accepting
   traffic on the LSP.  Nonetheless, MPLS Operations, Administration,
   and Maintenance (OAM) mechanisms, e.g., LSP ping and traceroute, as
   defined in [RFC4379] and [RFC6425], are expected to work
   independently of OOB mapping learning process.

   In order to avoid unnecessary use of the resources and possible
   black-holing of traffic, an egress LSR MAY send a Path Error message
   if the OOB mapping information is not received within a reasonable
   time.  This Path Error message SHOULD include the error code/sub-code
   "Notify Error / no OOB mapping received" for all affected LSPs.  If a
   notify request was included when the LSP was initially set up, a

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   Notify message (as defined in [RFC3473]) MAY also be used for
   delivery of this information to the ingress LSR.  An egress LSR MAY
   implement a cleanup timer for this purpose.  The time-out value is a
   local decision at the egress, with a RECOMMENDED default value of 60
   seconds.

3.  Security Considerations

   The addition of non-PHP behavior adds a variety of attacks on the
   label assigned by the egress node.  As change in the value of the
   egress label reported in the RRO can cause the LSP to be torn down,
   additional security considerations for protecting labels assigned by
   the egress node are required.  Security mechanisms as identified in
   [RFC5920], [RFC2205], [RFC3209], [RFC3473], [RFC5420], and [RFC4875]
   can be used for this purpose.  This document does not introduce any
   additional security issues above those identified in [RFC5920],
   [RFC2205], [RFC3209], [RFC3473], [RFC5420], and [RFC4875].

4.  IANA Considerations

   The following changes to the Resource Reservation Protocol - Traffic
   Engineering (RSVP-TE) Parameters registry are required.

4.1.  Attribute Flags for LSP Attributes Object

   The following new flags are defined for the Attributes Flags TLV in
   the LSP Attributes object.

   o  Non-PHP behavior flag:

      This flag is used in the Attributes Flags TLV in a Path message.
      The flag has a corresponding new flag to be used in the RRO
      Attributes subobject.  As per [RFC5420], the bit numbering in the
      Attribute Flags TLV and the RRO Attributes subobject is identical.
      That is, the same attribute is indicated by the same bit in both
      places.  This flag is not allowed in the Attributes Flags TLV in a
      Resv message.  Specifically, attributes of this flag are as
      follows:

      - Bit Number: 7

      - Attribute flag carried in Path message: Yes

      - Attribute flag carried in Resv message: No

      - Attribute flag carried in RRO message: Yes

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   o  OOB mapping flag:

      This flag is used in the Attributes Flags TLV in a Path message.
      The flag has a corresponding new flag to be used in the RRO
      Attributes subobject.  As per [RFC5420], the bit numbering in the
      Attribute Flags TLV and the RRO Attributes subobject is identical.
      That is, the same attribute is indicated by the same bit in both
      places.  This flag is not allowed in the Attributes Flags TLV in a
      Resv message.  Specifically, attributes of this flag are as
      follows:

      - Bit Number: 8

      - Attribute flag carried in Path message: Yes

      - Attribute flag carried in Resv message: No

      - Attribute flag carried in RRO message: Yes

4.2.  New RSVP Error Sub-Code

   For Error Code = 25 "Notify Error" (see [RFC3209]), the following
   sub-code is defined.

         Sub-code                    Value
         --------                    -----

         No OOB mapping received     12

5.  Acknowledgements

   The authors would like to thank Yakov Rekhter for his suggestions on
   this document.

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

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

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001.

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   [RFC3473]  Berger, L., Ed., "Generalized Multi-Protocol Label
              Switching (GMPLS) Signaling Resource ReserVation Protocol-
              Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
              January 2003.

   [RFC4875]  Aggarwal, R., Ed., Papadimitriou, D., Ed., and S.
              Yasukawa, Ed., "Extensions to Resource Reservation
              Protocol - Traffic Engineering (RSVP-TE) for Point-to-
              Multipoint TE Label Switched Paths (LSPs)", RFC 4875, May
              2007.

   [RFC5420]  Farrel, A., Ed., Papadimitriou, D., Vasseur, JP., and A.
              Ayyangarps, "Encoding of Attributes for MPLS LSP
              Establishment Using Resource Reservation Protocol Traffic
              Engineering (RSVP-TE)", RFC 5420, February 2009.

   [RFC6510]  Berger, L. and G. Swallow, "Resource Reservation Protocol
              (RSVP) Message Formats for Label Switched Path (LSP)
              Attributes Objects", RFC 6510, February 2012.

6.2.  Informative References

   [RFC4379]  Kompella, K. and G. Swallow, "Detecting Multi-Protocol
              Label Switched (MPLS) Data Plane Failures", RFC 4379,
              February 2006.

   [RFC4761]  Kompella, K., Ed., and Y. Rekhter, Ed., "Virtual Private
              LAN Service (VPLS) Using BGP for Auto-Discovery and
              Signaling", RFC 4761, January 2007.

   [RFC5920]  Fang, L., Ed., "Security Framework for MPLS and GMPLS
              Networks", RFC 5920, July 2010.

   [RFC5921]  Bocci, M., Ed., Bryant, S., Ed., Frost, D., Ed., Levrau,
              L., and L. Berger, "A Framework for MPLS in Transport
              Networks", RFC 5921, July 2010.

   [RFC6425]  Saxena, S., Ed., Swallow, G., Ali, Z., Farrel, A.,
              Yasukawa, S., and T. Nadeau, "Detecting Data-Plane
              Failures in Point-to-Multipoint MPLS - Extensions to LSP
              Ping", RFC 6425, November 2011.

   [RFC6513]  Rosen, E., Ed., and R. Aggarwal, Ed., "Multicast in
              MPLS/BGP IP VPNs", RFC 6513, February 2012.

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Authors' Addresses

   Zafar Ali
   Cisco Systems, Inc.
   EMail: zali@cisco.com

   George Swallow
   Cisco Systems, Inc.
   EMail: swallow@cisco.com

   Rahul Aggarwal
   Juniper Networks
   EMail: raggarwa_1@yahoo.com

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