Network Working Group                                        K. Kompella
Request for Comments: 3480                                    Y. Rekhter
Category: Standards Track                               Juniper Networks
                                                            A. Kullberg
                                                       NetPlane Systems
                                                          February 2003


                Signalling Unnumbered Links in CR-LDP
           (Constraint-Routing Label Distribution Protocol)

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 Constraint-Routing
  Label Distribution Protocol (CR-LDP), 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.





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  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 Objects.
  This document proposes simple procedures and extensions that allow
  CR-LDP signalling [CR-LDP] 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 CR-LDP 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 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 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]).




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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 REQUEST message used for
  establishing the LSP that forms the Forwarding Adjacency MUST contain
  an LSP_TUNNEL_INTERFACE_ID TLV (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 REQUEST message contains the LSP_TUNNEL_INTERFACE_ID TLV, then
  the tail-end LSR MUST allocate an identifier to that Forwarding
  Adjacency (just like for any other unnumbered link).  Furthermore,
  the MAPPING message for the LSP MUST contain an
  LSP_TUNNEL_INTERFACE_ID TLV, 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 Explicit Route TLV and the
  Interface ID TLV, 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 TLV (for the
  definition of Reverse Interface ID TLV see below).  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 TLV (for the
  definition of Forward Interface ID see below).

















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3.1. LSP_TUNNEL_INTERFACE_ID TLV

  The LSP_TUNNEL_INTERFACE ID TLV has Type 0x0836 and length 8.  The
  format is given below.

  Figure 1: LSP_TUNNEL_INTERFACE_ID TLV

   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |0|0|            Type           |            Length             |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                        LSR's Router ID                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Interface ID (32 bits)                     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  This TLV can optionally appear in either a REQUEST message or a
  MAPPING 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 Explicit Route TLV

  A new Type of ER-Hop TLV of the Explicit Route TLV is used to specify
  unnumbered links.  This Type is called Unnumbered Interface ID, and
  has the following format:

  The Type is 0x0837, and the Length is 12.  The L bit is set to
  indicate a loose hop, and cleared to indicate a strict hop.

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

  Figure 2: Unnumbered Interface ID

   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |0|0|          Type             |            Length = 12        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |L|                         Reserved                            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                           Router ID                           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                     Interface ID (32 bits)                    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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RFC 3480         Signalling Unnumbered Links in CR-LDP     February 2003


4.1. Processing the IF_ID TLV

  When an LSR receives a REQUEST message containing the IF_ID
  (Interface ID) TLV (see [GMPLS-CRLDP]) 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.

4.2. Processing the Unnumbered Interface ID ER-Hop TLV

  The Unnumbered Interface ID ER-Hop 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 Unnumbered Interface ID ER-Hop, 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
  Unnumbered Interface ID ER-Hop.

  With this in mind, the Explicit Route TLV processing in the presence
  of the Unnumbered Interface ID ER-Hop follows the rules specified in
  section 4.8.1 of [CR-LDP].

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

5. IANA Considerations

  RFC 3036 [LDP] defines the LDP TLV name space.  RFC 3212 [CD-LDP]
  further subdivides the range of that TLV space for TLVs associated
  with the CR-LDP in the range 0x0800 - 0x08FF, and defines the rules
  for the assignment of TLVs within that range using the terminology of
  BCP 26, RFC 2434, "Guidelines for Writing an IANA Considerations
  Section in RFCs".  Those rules apply to the assignment of TLV Types
  for the Unnumbered Interface ID and LSP_TUNNEL_INTERFACE_ID TLVs
  defined in this document.






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RFC 3480         Signalling Unnumbered Links in CR-LDP     February 2003


6. Security Considerations

  This document extends CR-LDP and raises no new security issues.  CR-
  LDP inherits the same security mechanism described in Section 4.0 of
  [LDP] to protect against the introduction of spoofed TCP segments
  into LDP session connection streams.

7. Acknowledgments

  Thanks to Rahul Aggarwal for his comments on the text.  Thanks also
  to Bora Akyol, Vach Kompella, and George Swallow.

8. References

8.1. Normative References

  [CR-LDP]      Jamoussi, B., Andersson, L., Callon, R., Dantu, R., Wu,
                L., Doolan, P., Worster, T., Feldman, N., Fredette, A.,
                Girish, M., Gray, E., Heinanen, J., Kilty, T. and A.
                Malis, "Constraint-Based LSP Setup using LDP", RFC
                3212, January 2002.

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

  [GMPLS-CRLDP] Ashwood, P., Ed. and L. Berger, "Generalized Multi-
                Protocol Label Switching (GMPLS) Signaling Constraint-
                based Routed Label Distribution Protocol (CR-LDP)
                Extensions", RFC 3472 January 2003.

  [LDP]         Andersson, L., Doolan, P., Feldman, N., Fredette, A.
                and B. Thomas, "LDP Specification", RFC 3036, January
                2001

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

8.2. Informative References

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

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





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RFC 3480         Signalling Unnumbered Links in CR-LDP     February 2003


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

  [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.

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

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

9. Authors' Addresses

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

  EMail: [email protected]

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

  EMail: [email protected]

  Alan Kullberg
  NetPlane Systems, Inc.
  Westwood Executive Center
  200 Lowder Brook Drive
  Westwood, MA  02090

  EMail: [email protected]











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RFC 3480         Signalling Unnumbered Links in CR-LDP     February 2003


10.  Full Copyright Statement

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

  This document and translations of it may be copied and furnished to
  others, and derivative works that comment on or otherwise explain it
  or assist in its implementation may be prepared, copied, published
  and distributed, in whole or in part, without restriction of any
  kind, provided that the above copyright notice and this paragraph are
  included on all such copies and derivative works.  However, this
  document itself may not be modified in any way, such as by removing
  the copyright notice or references to the Internet Society or other
  Internet organizations, except as needed for the purpose of
  developing Internet standards in which case the procedures for
  copyrights defined in the Internet Standards process must be
  followed, or as required to translate it into languages other than
  English.

  The limited permissions granted above are perpetual and will not be
  revoked by the Internet Society or its successors or assigns.

  This document and the information contained herein is provided on an
  "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
  TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
  BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
  HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
  MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

  Funding for the RFC Editor function is currently provided by the
  Internet Society.



















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