Network Working Group Kireeti Kompella
Internet Draft Juniper Networks
Expiration Date: May 2001 Yakov Rekhter
Juniper Networks
Signalling Unnumbered Links in RSVP-TE
draft-ietf-mpls-rsvp-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
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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 [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 procedures and extensions
that allow RSVP-TE signalling [RSVP-TE] 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 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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5. 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
Path message 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 LSP's interface ID. If
the LSP is part of a bundled link (see [BUNDLE]), the Interface ID is
set to the component interface ID of the LSP.
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 ID 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 reverse LSP's interface ID. If the LSP is part of a bundled
link (see [BUNDLE]), the Component Interface ID is set to the
component interface ID of the LSP; otherwise, it is set to zero.
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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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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This subobject MUST be strict (i.e., the L bit MUST be 0). The Type
is 4 (Unnumbered Interface ID). The Length is 12.
6.1. Interpreting the Unnumbered Interface ID Subobject
The Router ID (say X) is the router ID of the LSR P at the upstream
end of the unnumbered link. The Interface ID (say I) is the outgoing
interface identifier with respect to the LSR specified by the router
ID. The PHOP object in the message MUST contain X. If not, the
receiving node MUST return a PathErr.
6.2. Validating the Unnumbered Interface ID Subobject
First of all, the receiving node R 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. R
looks up in its Traffic Engineering database the node P corresponding
to the router ID X in the ERO subobject. It then checks that there
is a link from P to R that carries the same Interface ID as the one
in the ERO subobject (I). If this is not the case, R has received
the message in error and SHOULD return a "Bad initial subobject"
error.
For other types of ERO subobjects, the rules in [RSVP-TE] apply.
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6.3. Determining the Link Identified by the ERO
Determining the link for which label allocation must be done depends
on whether a COMPONENT_INTERFACE_ID [BUNDLE] is present in the Path
message or not. If so, set ID to the Component Interface ID;
otherwise, set ID to I (the Interface ID in the ERO subobject). X is
(as above) the router ID in the Unnumbered ERO subobject.
First, R checks whether the tuple <X, ID> matches the tuple <LSR's
Router ID, Forward Interface ID> of any of the LSPs for which the
node is a tail-end. If a match is found, the match identifies the
Forwarding Adjacency for which the node has to perform label
allocation.
Otherwise, the node MUST check whether the tuple <X, ID> matches the
tuple <LSR's Router ID, Reverse Interface ID> of any of the
bidirectional LSPs for which the node is the head-end. If a match is
found, the match identifies the Forwarding Adjacency for which the
node has to perform label allocation, namely, the reverse Forwarding
Adjacency for the LSP identified by the match.
Otherwise, R must have information about Interface IDs and Component
Interface IDs assigned by its neighbors for the unnumbered links
between R and its neighbors (i.e., incoming interface identifiers
from R's point of view).
If the Path message does not contain a COMPONENT_INTERFACE_ID, R
determines the link by looking up <X, I> in the Traffic Engineering
database. If the Path message contains a COMPONENT_INTERFACE_ID, R
determines the link as described in [BUNDLE].
Otherwise, it is assumed that the node has to perform label
allocation for the link over which the Path message was received.
6.4. Selecting the Next Hop
Once the link has been determined, the initial subobject is removed,
and the next hop should be computed. The next hop for an Unnumbered
Interface ID subobject is determined as follows. The Interface ID
MUST refer to an outgoing interface identifier that this 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. If this node is R itself, the
subobject is removed, and the process repeated. If the next node is
not R, say N, this is the next hop to which a Path message must be
sent.
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Furthermore, when sending a Path message to N, the ERO to be used is
the remaining ERO (i.e., starting with the subobject that refers to a
node different from the receiving node); the PHOP object is R's
router ID.
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)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID (32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Type is 4 (Unnumbered Interface ID); the Length is 8. 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
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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).
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
[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)
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[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)
12. Author Information
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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