Network Working Group Kireeti Kompella
Internet Draft Juniper Networks
Expiration Date: August 2002 Yakov Rekhter
Juniper Networks
Signalling Unnumbered Links in RSVP-TE
draft-ietf-mpls-rsvp-unnum-04.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.
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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
RSVP-TE, one of the MPLS TE signalling protocols, 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 [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 [GMPLS-RSVP] to be used with unnumbered
links.
4. 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. 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
idenfitier for that link. So is 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.
This section is equally applicable to the case of unnumbered
component links (see [LINK-BUNDLE]).
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5. 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.
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.
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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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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6. 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.
6.1. Processing the IF_ID RSVP_HOP object
When an LSR receives a Path message containing the IF_ID RSVP_HOP
object (see [GMPLS-RSVP]) 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.
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6.2. Processing the ERO object
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
(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 [RSVP-TE].
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.
7. 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
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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.
8. Security Considerations
This document raises no new security concerns for RSVP.
9. 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).
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10. 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.
11. References
[LINK-BUNDLE] Kompella, K., Rekhter, Y., and Berger, L., "Link
Bundling in MPLS Traffic Engineering", draft-kompella-mpls-
bundle-05.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)
[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)
[GMPLS-ISIS] Kompella, K., Rekhter, Y., Banerjee, A. et al, "IS-IS
Extensions in Support of Generalized MPLS", draft-ietf-isis-gmpls-
extensions-02.txt (work in progress)
[GMPLS-OSPF] Kompella, K., Rekhter, Y., Banerjee, A. et al, "OSPF
Extensions in Support of Generalized MPLS", draft-ietf-ccamp-ospf-
gmpls-extensions-00.txt (work in progress)
[GMPLS-RSVP] Ashwood, P., et al., "Generalized MPLS Signalling RSVP-
TE Extensions", draft-ietf-mpls-generalized-rsvp-te-04.txt
12. Author Information
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Internet Draft draft-ietf-mpls-rsvp-unnum-04.txt February 2002
Kireeti Kompella
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
e-mail: kireeti@juniper.net
Yakov Rekhter
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, CA 94089
e-mail: yakov@juniper.net
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