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Network Working Group                             Kireeti Kompella
Internet Draft                                    Juniper Networks
Expiration Date: February 2001                       Yakov Rekhter
                                                     Cisco Systems


               Traffic Engineering with Unnumbered Links

                    draft-kompella-mpls-unnum-01.txt


1. 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 groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as ``work in progress.''

   The list of current Internet-Drafts can be accessed at
   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.


2. Abstract

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












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3. 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 [ISIS-TE, OSPF-TE]. 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 extensions to these two
   objects that allows MPLS TE signalling to be used with unnumbered
   links.


4. 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 16-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.  A good
   candidate for the interface identifier is the SNMP IfIndex of the
   link, if it exists.

   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.  There is no a priori relationship
   between the two interface identifiers.














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5. 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:

       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    |     Interface ID (16 bits)    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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


5.1. Interpreting the Unnumbered Interface ID Subobject

   The Interface ID is the outgoing interface identifier with respect to
   the previous node in the path (i.e., the PHOP).  If the Path message
   contains an Unnumbered Interface ID subobject as the first subobject
   in the ERO, then the PHOP object in the message must contain the
   router ID of the previous node.


5.2. Processing the Unnumbered Interface ID Subobject

   On receiving an ERO with an Unnumbered Interface ID subobject as the
   first subobject, the receiving node MAY validate that it received the
   Path Message correctly.  To do so, the node must maintain a database
   of Traffic Engineering information distributed by IS-IS and/or OSPF.

   To validate that it received the Path message correctly, the node
   looks up in its Traffic Engineering database for the node
   corresponding to the router ID in the PHOP object in the Path
   message. It then checks that there is a link from the previous node
   to itself that carries the same Interface ID as the one in the ERO
   subobject. If this is not the case, the receiving node has received
   the message in error and SHOULD return a "Bad initial subobject"
   error.  Otherwise, the receiving node removes the first subobject,
   and continues processing the ERO.


5.3. Selecting the Next Hop

   If, after processing and removing all initial subobjects in the ERO
   that refer to itself, the receiving node finds a subobject of type
   Unnumbered Interface ID, it determines the next hop as follows.  The
   Interface ID MUST refer to an outgoing interface identifier that this



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   node allocated; if not, the node SHOULD return a "Bad EXPLICIT_ROUTE
   object" error.  The next hop is the node at the other end of the link
   that the Interface ID refers to.

   Furthermore, when sending a Path message to the next hop, the ERO to
   be used is the current ERO (starting with the Unnumbered Interface ID
   subobject); the PHOP object is the sending node's router ID.


5.4. Unnumbered Forwarding Adjacencies

   If an LSR that originates an LSP advertises this LSP as an unnumbered
   Forwarding Adjacency in IS-IS or OSPF [LSP-HIER], the LSR MUST
   allocate an interface ID to that Forwarding Adjacency.  Moreover, the
   Tunnel ID in the Session Object of the LSP MUST be set to that
   interface ID, and the Extended Tunnel ID in the Session Object of the
   LSP MUST be set to the Router ID of the LSR that originates the LSP.

   A node that receives a Path message with an Unnumbered Interface ID
   as the first subobject in the ERO carried by the message checks
   whether the tuple <PHOP, Interface ID> matches the tuple <Extended
   Tunnel ID, Tunnel ID> of any of the LSPs for which the node is an
   egress. If the match is found, the match identifies the Forwarding
   Adjacency for which the node has to perform label allocation.


6. 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)|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Reserved (must be zero)    |     Interface ID (16 bits)    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Type is 4 (Unnumbered Interface ID); the Length is 8.  Flags are
   defined below.









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6.1. Flags

      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).


6.2. Handling RRO

   If at an intermediate node (or at the ingress), 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.


7. Security Considerations

   This document raises no new security concerns for RSVP.


8. 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.






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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 for his comments on the text.


10. References

   [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-06.txt (work in progress)

   [ISIS-TE] Smit, H., and Li, T., "IS-IS extensions for Traffic
   Engineering", draft-ietf-isis-traffic-01.txt (work in progress)

   [OSPF-TE] Katz, D., and Yeung, D., "Traffic Engineering Extensions to
   OSPF", draft-katz-yeung-ospf-traffic-01.txt (work in progress)

   [LSP-HIER] Kompella, K., and Rekhter, Y., "LSP Hierarchy with MPLS
   TE", draft-ietf-mpls-lsp-hierarchy-00.txt (work in progress)


11. Author Information


Kireeti Kompella
Juniper Networks, Inc.
385 Ravendale Drive
Mountain View, CA 94043
e-mail: kireeti@juniper.net

Yakov Rekhter
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
e-mail: yakov@cisco.com














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