Network Working Group                             Kireeti Kompella
Internet Draft                                    Juniper Networks
Expiration Date: February 2002                       Yakov Rekhter
                                                  Juniper Networks


                 Signalling Unnumbered Links in RSVP-TE

                   draft-ietf-mpls-rsvp-unnum-02.txt


. Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
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   and may be updated, replaced, or obsoleted by other documents at any
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   material or to cite them other than as ``work in progress.''

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   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.


. Abstract

   Current signalling used by MPLS TE doesn't provide support for
   unnumbered links. This document defines procedures and extensions to
   RSVP-TE, one of the MPLS TE signalling protocols, that are needed in
   order to support unnumbered links.













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. 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 doesn't provide support for
   unnumbered links because the current signalling doesn't 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 [RSVP-TE] to be used with unnumbered links.


. Interface Identifiers

   Since unnumbered links are not identified by an IP address, then for
   the purpose of MPLS TE they need some other identifier. We assume
   that each unnumbered link on a Label Switched Router (LSR) is given a
   unique 32-bit identifier. The scope of this identifier is the LSR to
   which the link belongs; moreover, the IS-IS and/or OSPF and RSVP
   modules on an LSR must agree on interface identifiers.

   Note that links are directed, i.e., a link l is from some LSR A to
   some other LSR B. LSR A chooses the interface identifier for link l.
   To be completely clear, we call this the "outgoing interface
   identifier from LSR A's point of view". If there is a reverse link
   from LSR B to LSR A (for example, a point-to-point SONET interface
   connecting LSRs A and B would be represented as two links, one from A
   to B, and another from B to A), B chooses the outgoing interface
   identifier for the reverse link; we call this the link's "incoming
   interface identifier from A's point of view". There is no a priori
   relationship between the two interface identifiers.
















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. 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 [BUNDLE]), the LSR MUST
   allocate an interface 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 an 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 interface identifier that the LSR allocated to the
   Forwarding Adjacency.

   If the LSP is bidirectional, and the tail-end LSR (of the forward
   LSP) advertises the reverse LSP as an unnumbered Forwarding
   Adjacency, the tail-end LSR MUST allocate an interface identifier to
   the reverse Forwarding Adjacency. 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 interface identifier allocated by the tail-end LSR.


5.1. LSP_TUNNEL_INTERFACE_ID Object

   The LSP_TUNNEL_INTERFACE_ID object has a class number of type
   11bbbbbb (to be assigned by IANA), 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.







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. 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)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   This subobject MUST be strict (i.e., the L bit MUST be 0). The Type
   is 4 (Unnumbered Interface ID). The Length is 12.

   The Interface ID is the outgoing interface identifier with respect to
   the LSR specified by the router ID.


6.1. Processing the Unnumbered Interface ID Subobject

   First of all, the receiving LSR must validate that it received the
   Path message correctly. If the first subobject in the ERO is an
   Unnumbered Interface subobject, the check is done as follows (for
   other types of ERO subobjects, the rules in [RSVP-TE] apply).

   The PHOP or IF_ID RSVP_HOP object in the message MUST contain the
   same Router ID (IP Address) as the Router ID carried in the
   subobject.  If not, the receiving LSR MUST return a PathErr.  If
   IF_ID RSVP_HOP object is present, and it carries the IF_INDEX TLV,
   the receiving LSR SHOULD check that the value carried in this TLV is
   the same as carried in the subobject. If the value is different, the
   receiving LSR MUST return a PathErr.

   If the above checks are passes, the LSR checks whether the tuple
   <Router ID, Interface ID> from the Unnumbered Interface subobject
   matches the tuple <Router ID, Forward Interface ID> of any of the
   LSPs for which the LSR is a tail-end. If a match is found, the match
   identifies the Forwarding Adjacency for which the LSR has to perform
   label allocation.

   Otherwise, the LSR MUST check whether the tuple <Router ID, Interface



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   ID> from the Unnumbered Interface subobject matches the tuple <Router
   ID, Reverse Interface ID> of any of the bidirectional LSPs for which
   the LSR is the head-end. If a match is found, the match identifies
   the Forwarding Adjacency for which the LSR has to perform label
   allocation, namely, the reverse Forwarding Adjacency for the LSP
   identified by the match.

   Otherwise, the LSR must have information about the identifiers
   assigned by its neighbors to the unnumbered links (i.e., incoming
   interface identifiers from LSR's point of view). The LSR uses this
   information to find a link with tuple <Router ID, incoming interface
   identifier> matching the tuple <Router ID, Interface ID> from the
   Unnumbered Interface subobject. If the matching tuple is found, and
   the link is not a bundled link, the match identifies the link for
   which the LSR has to perform label allocation. If the matching tuple
   is found, and the link is a bundled link, the LSR follows the
   procedures for label allocation as described in [LINK-BUNDLE].

   Otherwise, the LSR SHOULD return a "Bad initial subobject" error.


6.2. Selecting the Next Hop

   Once an LSR determines the link for which the LSR has to perform
   label allocation, the LSR removes the initial subobject in the ERO,
   and computes the next hop. The next hop for an Unnumbered Interface
   subobject is computed as follows. The Interface ID in the subobject
   MUST refer to an outgoing interface identifier that this node
   allocated; if not, the LSR SHOULD return a "Bad EXPLICIT_ROUTE
   object" error. The next hop is the LSR at the other end of the link
   that the Interface ID refers to. If this is the LSR itself, the
   subobject is removed, and the process repeated. If the next hop is
   some other LSR, then this is the next hop to which a Path message
   must be sent.

   When sending a Path message to the next hop, if the Path message
   carries the PHOP object, then this object MUST contain the LSR's
   Router ID. If the Path message carries the IF_ID object, then this
   object MUST contain the IF_INDEX TLV, with IP Address in that TLV set
   to the LSR's Router ID, and Interface ID set to the Interface ID
   carried in the first subobject of the ERO.










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. 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_ATTRIBUITE
            object of the cooresponding Path message.

      0x02  Local protection in use

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


7.1. 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 [RSVP-TE] apply. Also, if
   Label Recording is desired, the procedures of [RSVP-TE] apply.






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. Security Considerations

   This document raises no new security concerns for RSVP.


. IANA Considerations

   The responsible Internet authority (presently called 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 [RSVP-TE], using the terminology of BCP
   26 "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., this is an 8-bit number whose two most
   significant bits are 1).


. 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 and Vach Kompella.


. References

   [BUNDLE] Kompella, K., Rekhter, Y., and Berger, L., "Link Bundling in
   MPLS Traffic Engineering", draft-kompella-mpls-bundle-05.txt (work in
   progress)

   [ISIS-TE] Smit, H., and Li, T., "IS-IS extensions for Traffic
   Engineering", draft-ietf-isis-traffic-02.txt (work in progress)

   [LSP-HIER] Kompella, K., and Rekhter, Y., "LSP Hierarchy with MPLS
   TE", draft-ietf-mpls-lsp-hierarchy-02.txt (work in progress)

   [OSPF-TE] Katz, D., and Yeung, D., "Traffic Engineering Extensions to
   OSPF", draft-katz-yeung-ospf-traffic-04.txt (work in progress)

   [RSVP-TE] Awduche, D., Berger, L., Gan, D. H., Li, T., Srinivasan,
   V., and Swallow, G., "RSVP-TE: Extensions to RSVP for LSP Tunnels",
   draft-ietf-mpls-rsvp-lsp-tunnel-08.txt (work in progress)



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. Author Information


Kireeti Kompella
Juniper Networks, Inc.
 N. Mathilda Ave.
Sunnyvale, CA 94089
e-mail: kireeti@juniper.net

Yakov Rekhter
Juniper Networks, Inc.
 N. Mathilda Ave.
Sunnyvale, CA 94089
e-mail: yakov@juniper.net





































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