Internet Draft
Network Working Group Kireeti Kompella
Internet Draft Juniper Networks
Expiration Date: March 2001 Yakov Rekhter
Cisco Systems
Traffic Engineering with Unnumbered Links
draft-kompella-mpls-unnum-02.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
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 [RSVP-TE, CR-LDP] 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
and/or CR-LDP 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. 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
Tunnel ID in the Session Object of the Path Message for 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.
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, it MUST set the "Reverse
Interface ID" field in the Filter Specification object in the flow
descriptor list for this LSP to the reverse FA's interface ID (note
that while in general there can be multiple Filter Specifications, it
is expected in the case of point-to-point LSPs that there is only
one). To accommodate this, the LSP_TUNNEL_IPv4 Filter Specification
Object's format is modified per Figure 1:
Figure 1: LSP_TUNNEL_IPv4 Filter Specification 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 tunnel sender address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Interface ID | LSP ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6. Signalling Unnumbered Links in EROs
A new subobject of the Explicit Route Object (ERO) is used to specify
unnumbered links. In RSVP, this subobject has the following format:
Figure 2: Unnumbered Interface ID Subobject in RSVP
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.
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In CR-LDP, this subobject has the following format:
Figure 3: Unnumbered Interface ID Subobject in CR-LDP
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| MUST be zero | Interface ID (16 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This subobject MUST be strict (i.e., the L bit MUST be 0). The Type
is 0x0805 (Unnumbered Interface ID) and the Length is 4.
6.1. 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.
6.2. Processing the Unnumbered Interface ID Subobject
A node that receives a Path message with an Unnumbered Interface ID
as the first subobject in the ERO carried by the message MUST check
whether the tuple matches the tuple 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
matches the tuple 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, it is assumed that the node has to perform label
allocation for the link over which the Path message was received. In
this case the receiving node MAY validate that it received the
Path/Request Message correctly. To do so, the node must maintain a
database of Traffic Engineering information distributed by IS-IS
and/or OSPF.
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To validate that it received the Path/Request 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 (or
sender of the Request 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.
6.3. 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
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/Request message to the next hop, the
ERO to be used is the current ERO (starting with the Unnumbered
Interface ID subobject); for RSVP, the PHOP object is the sending
node'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. In RSVP, 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.
This does not apply to CR-LDP.
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7.1. 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).
7.2. 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 or CR-LDP.
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.
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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.
11. References
[CR-LDP] Jamoussi, B., editor, "Constraint-Based LSP Setup using
LDP", draft-ietf-mpls-cr-ldp-04.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-01.txt (work in progress)
[OSPF-TE] Katz, D., and Yeung, D., "Traffic Engineering Extensions to
OSPF", draft-katz-yeung-ospf-traffic-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-07.txt (work in progress)
12. 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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