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IETF RFC 3477
Signalling Unnumbered Links in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)
Last modified on Thursday, February 13th, 2003
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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 © 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
[RFC 2119].
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.
Kompella & Rekhter Standards Track PAGE 1 
RFC 3477 Signalling Unnumbered Links in RSVP-TE January 2003
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 [RFC 3473] 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]).
Kompella & Rekhter Standards Track PAGE 2
RFC 3477 Signalling Unnumbered Links in RSVP-TE January 2003
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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RFC 3477 Signalling Unnumbered Links in RSVP-TE January 2003
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 [RFC 3473], [RFC 3471]) 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 [RFC 3473], [RFC 3471]). 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
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RFC 3477 Signalling Unnumbered Links in RSVP-TE January 2003
(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 [RFC 3209].
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).
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RFC 3477 Signalling Unnumbered Links in RSVP-TE January 2003
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 [RFC 3209] apply. Also, if
Label Recording is desired, the procedures of [RFC 3209] apply.
6. Security Considerations
This document makes a small extension to RFC 3209 [RFC 3209] 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 [RFC 3209], 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
Kompella & Rekhter Standards Track PAGE 6
RFC 3477 Signalling Unnumbered Links in RSVP-TE January 2003
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
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 3209] 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.
[RFC 3471] Berger, L., Editor, "Generalized Multi-Protocol Label
Switching (MPLS) Signaling Functional Description", RFC
3471, January 2003.
[RFC 3473] 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.
Kompella & Rekhter Standards Track PAGE 7
RFC 3477 Signalling Unnumbered Links in RSVP-TE January 2003
[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
Kompella & Rekhter Standards Track PAGE 8
RFC 3477 Signalling Unnumbered Links in RSVP-TE January 2003
12. Full Copyright Statement
Copyright © 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
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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
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Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Kompella & Rekhter Standards Track PAGE 9
Signalling Unnumbered Links in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)
RFC TOTAL SIZE: 19899 bytes
PUBLICATION DATE: Thursday, February 13th, 2003
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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