Internet Draft
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
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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
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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 matches the tuple 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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