RSVP-TE unnumbered links: Signalling Unnumbered Links in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)

Network Working Group                                        K. Kompella
Request for Comments: 3477                                    Y. Rekhter
Category: Standards Track                               Juniper Networks
                                                            January 2003


     Signalling Unnumbered Links in Resource ReSerVation Protocol -
                     Traffic Engineering (RSVP-TE)

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   Current signalling used by Multi-Protocol Label Switching Traffic
   Engineering (MPLS TE) does not provide support for unnumbered links.
   This document defines procedures and extensions to Resource
   ReSerVation Protocol (RSVP) for Label Switched Path (LSP) Tunnels
   (RSVP-TE), one of the MPLS TE signalling protocols, that are needed
   in order to support unnumbered links.

Specification of Requirements

   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 BCP 14, RFC 2119
   [RFC2119].

1. Overview

   Supporting MPLS TE over unnumbered links (i.e., links that do not
   have IP addresses) involves two components: (a) the ability to carry
   (TE) information about unnumbered links in IGP TE extensions (ISIS or
   OSPF), and (b) the ability to specify unnumbered links in MPLS TE
   signalling.  The former is covered in [GMPLS-ISIS, GMPLS-OSPF].  The
   focus of this document is on the latter.

   Current signalling used by MPLS TE does not provide support for
   unnumbered links because the current signalling does not provide a
   way to indicate an unnumbered link in its Explicit Route and Record
   Route Objects.  This document proposes simple procedures and
   extensions that allow RSVP-TE signalling [RFC3473] to be used with
   unnumbered links.

2. Link Identifiers

   An unnumbered link has to be a point-to-point link.  An LSR at each
   end of an unnumbered link assigns an identifier to that link.  This
   identifier is a non-zero 32-bit number that is unique within the
   scope of the LSR that assigns it.  If one is using OSPF or ISIS as
   the IGP in support of traffic engineering, then the IS-IS and/or OSPF
   and RSVP modules on an LSR must agree on the identifiers.

   There is no a priori relationship between the identifiers assigned to
   a link by the LSRs at each end of that link.

   LSRs at the two end points of an unnumbered link exchange with each
   other the identifiers they assign to the link.  Exchanging the
   identifiers may be accomplished by configuration, by means of a
   protocol such as LMP ([LMP]), by means of RSVP/CR-LDP (especially in
   the case where a link is a Forwarding Adjacency, see below), or by
   means of IS-IS or OSPF extensions ([ISIS-GMPLS], [OSPF-GMPLS]).

   Consider an (unnumbered) link between LSRs A and B.  LSR A chooses an
   identifier for that link.  So does LSR B.  From A's perspective, we
   refer to the identifier that A assigned to the link as the "link
   local identifier" (or just "local identifier"), and to the identifier
   that B assigned to the link as the "link remote identifier" (or just
   "remote identifier").  Likewise, from B's perspective, the identifier
   that B assigned to the link is the local identifier, and the
   identifier that A assigned to the link is the remote identifier.

   In the context of this document the term "Router ID" means a stable
   IP address of an LSR that is always reachable if there is any
   connectivity to the LSR.  This is typically implemented as a
   "loopback address"; the key attribute is that the address does not
   become unusable if an interface on the LSR is down.  In some cases
   this value will need to be configured.  If one is using the OSPF or
   ISIS as the IGP in support of traffic engineering, then it is
   RECOMMENDED for the Router ID to be set to the "Router Address" as
   defined in [OSPF-TE], or "Traffic Engineering Router ID" as defined
   in [ISIS-TE].

   This section is equally applicable to the case of unnumbered
   component links (see [LINK-BUNDLE]).

3. Unnumbered Forwarding Adjacencies

   If an LSR that originates an LSP advertises this LSP as an unnumbered
   Forwarding Adjacency in IS-IS or OSPF (see [LSP-HIER]), or the LSR
   uses the Forwarding Adjacency formed by this LSP as an unnumbered
   component link of a bundled link (see [LINK-BUNDLE]), the LSR MUST
   allocate an identifier to that Forwarding Adjacency (just like for
   any other unnumbered link).  Moreover, the Path message used for
   establishing the LSP that forms the Forwarding Adjacency MUST contain
   the LSP_TUNNEL_INTERFACE_ID object (described below), with the LSR's
   Router ID set to the head end's Router ID, and the Interface ID set
   to the identifier that the LSR allocated to the Forwarding Adjacency.

   If the Path message contains the LSP_TUNNEL_INTERFACE_ID object, then
   the tail-end LSR MUST allocate an identifier to that Forwarding
   Adjacency (just like for any other unnumbered link).  Furthermore,
   the Resv message for the LSP MUST contain an LSP_TUNNEL_INTERFACE_ID
   object, with the LSR's Router ID set to the tail-end's Router ID, and
   the Interface ID set to the identifier allocated by the tail-end LSR.

   For the purpose of processing the ERO and the IF_ID RSVP_HOP objects,
   an unnumbered Forwarding Adjacency is treated as an unnumbered (TE)
   link or an unnumbered component link as follows.  The LSR that
   originates the Adjacency sets the link local identifier for that link
   to the value that the LSR allocates to that Forwarding Adjacency, and
   the link remote identifier to the value carried in the Interface ID
   field of the Reverse Interface ID object.  The LSR that is a tail-end
   of that Forwarding Adjacency sets the link local identifier for that
   link to the value that the LSR allocates to that Forwarding
   Adjacency, and the link remote identifier to the value carried in the
   Interface ID field of the Forward Interface ID object.

3.1. LSP_TUNNEL_INTERFACE_ID Object

   The LSP_TUNNEL_INTERFACE_ID object has a class number of of 193, C-
   Type of 1 and length of 12.  The format is given below.

   Figure 1: LSP_TUNNEL_INTERFACE_ID Object

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        LSR's Router ID                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Interface ID (32 bits)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   This object can optionally appear in either a Path message or a Resv
   message.  In the former case, we call it the "Forward Interface ID"
   for that LSP; in the latter case, we call it the "Reverse Interface
   ID" for the LSP.

4. Signalling Unnumbered Links in EROs

   A new subobject of the Explicit Route Object (ERO) is used to specify
   unnumbered links.  This subobject has the following format:

   Figure 2: Unnumbered Interface ID Subobject

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |L|    Type     |     Length    |    Reserved (MUST be zero)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Router ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Interface ID (32 bits)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type is 4 (Unnumbered Interface ID).  The Length is 12.

   The Interface ID is the identifier assigned to the link by the LSR
   specified by the router ID.

4.1. Processing the IF_ID RSVP_HOP object

   When an LSR receives a Path message containing the IF_ID RSVP_HOP
   object (see [RFC3473], [RFC3471]) with the IF_INDEX TLV, the LSR
   processes this TLV as follows.  The LSR must have information about
   the identifiers assigned by its neighbors to the unnumbered links
   between the neighbors and the LSR.  The LSR uses this information to
   find a link with tuple <Router ID, local identifier> matching the
   tuple <IP Address, Interface ID> carried in the IF_INDEX TLV.  If the
   matching tuple is found, the match identifies the link for which the
   LSR has to perform label allocation.

   Otherwise, the LSR SHOULD return an error using the IF_ID ERROR_SPEC
   object (see [RFC3473], [RFC3471]).  The Error code in the object is
   set to 24.  The Error value in the object is set to 16.

4.2. Processing the ERO

   The Unnumbered Interface ID subobject is defined to be a part of a
   particular abstract node if that node has the Router ID that is equal
   to the Router ID field in the subobject, and if the node has an
   (unnumbered) link or an (unnumbered) Forwarding Adjacency whose local
   identifier (from that node's point of view) is equal to the value
   carried in the Interface ID field of the subobject.

   With this in mind, the ERO processing in the presence of the
   Unnumbered Interface ID subobject follows the rules specified in
   section 4.3.4.1 of [RFC3209].

   As part of the ERO processing, or to be more precise, as part of the
   next hop selection, if the outgoing link is unnumbered, the Path
   message that the node sends to the next hop MUST include the IF_ID
   RSVP_HOP object, with the IP address field of that object set to the
   Router ID of the node, and the Interface ID field of that object set
   to the identifier assigned to the link by the node.

5. Record Route Object

   A new subobject of the Record Route Object (RRO) is used to record
   that the LSP path traversed an unnumbered link.  This subobject has
   the following format:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |     Length    |     Flags     | Reserved (MBZ)|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           Router ID                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     Interface ID (32 bits)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type is 4 (Unnumbered Interface ID); the Length is 12.  Flags are
   defined below.

   0x01  Local protection available

      Indicates that the link downstream of this node is protected via a
      local repair mechanism.  This flag can only be set if the Local
      protection flag was set in the SESSION_ATTRIBUTE object of the
      corresponding Path message.

   0x02  Local protection in use

      Indicates that a local repair mechanism is in use to maintain this
      tunnel (usually in the face of an outage of the link it was
      previously routed over).

5.1. Handling RRO

   If at an intermediate node (or at the head-end), the ERO subobject
   that was used to determine the next hop is of type Unnumbered
   Interface ID, and a RRO object was received in the Path message (or
   is desired in the original Path message), an RRO subobject of type
   Unnumbered Interface ID MUST be appended to the received RRO when
   sending a Path message downstream.

   If the ERO subobject that was used to determine the next hop is of
   any other type, the handling procedures of [RFC3209] apply.  Also, if
   Label Recording is desired, the procedures of [RFC3209] apply.

6. Security Considerations

   This document makes a small extension to RFC 3209 [RFC3209] to refine
   and explicate the use of unnumbered links.  As such it poses no new
   security concerns.  In fact, one might argue that use of the extra
   interface identify could make an RSVP message harder to spoof.

7. IANA Considerations

   The IANA assigns values to RSVP protocol parameters.  The current
   document defines a new subobject for the EXPLICIT_ROUTE object and
   for the ROUTE_RECORD object.  The rules for the assignment of
   subobject numbers have been defined in [RFC3209], using the
   terminology of BCP 26, RFC 2434, "Guidelines for Writing an IANA
   Considerations Section in RFCs".  Those rules apply to the assignment
   of subobject numbers for the new subobject of the EXPLICIT_ROUTE and
   ROUTE_RECORD objects.

   Furthermore, the same Internet authority needs to assign a class
   number to the LSP_TUNNEL_INTERFACE_ID object.  This must be of the
   form 11bbbbbb (i.e., RSVP silently ignores this unknown object but
   forwards it).

8. Intellectual Property Considerations

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights.  Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11.  Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard.  Please address the information to the IETF Executive
   Director.

9. Acknowledgments

   Thanks to Lou Berger and Markus Jork for pointing out that the RRO
   should be extended in like fashion to the ERO.  Thanks also to Rahul
   Aggarwal and Alan Kullberg for their comments on the text.  Finally,
   thanks to Bora Akyol, Vach Kompella, and George Swallow.

10. References

10.1. Normative references

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

   [RFC3471]     Berger, L., Editor, "Generalized Multi-Protocol Label
                 Switching (MPLS) Signaling Functional Description", RFC
                 3471, January 2003.

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

10.2. Non-normative references

   [GMPLS-ISIS]  Kompella, K., Rekhter, Y., Banerjee, A. et al., "IS-IS
                 Extensions in Support of Generalized MPLS", Work in
                 Progress.

   [GMPLS-OSPF]  Kompella, K., Rekhter, Y., Banerjee, A. et al., "OSPF
                 Extensions in Support of Generalized MPLS", Work in
                 Progress.

   [ISIS-TE]     Li, T. and H. Smit, "IS-IS extensions for Traffic
                 Engineering", Work in Progress.

   [LINK-BUNDLE] Kompella, K., Rekhter, Y. and L. Berger, "Link Bundling
                 in MPLS Traffic Engineering", Work in Progress.

   [LSP-HIER]    Kompella, K. and Y. Rekhter, "LSP Hierarchy with MPLS
                 TE", Work in Progress.

   [LMP]         Lang, J., Mitra, K., et al., "Link Management Protocol
                 (LMP)", Work in Progress.

   [OSPF-TE]     Katz, D., Yeung, D., Kompella, K., "Traffic Engineering
                 Extensions to OSPF Version 2", Work in Progress.

11. Authors' Addresses

   Kireeti Kompella
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA 94089

   EMail: kireeti@juniper.net


   Yakov Rekhter
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA 94089

   EMail: yakov@juniper.net

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