Internet Draft Jean-Philippe Vasseur (Editor)
MPLS WG Zafar Ali
Siva Sivabalan
Cisco Systems, Inc.
Proposed Status: Standard
Expires: November 2005
May 2005
draft-ietf-mpls-nodeid-subobject-06.txt
Definition of an RRO node-id subobject
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draft-ietf-mpls-nodeid-subobject-06.txt May 2005
Abstract
In the context of MPLS TE Fast Reroute, the Merge Point (MP) address is
required at the Point of Local Repair (PLR) in order to select a backup
tunnel intersecting a fast reroutable Traffic Engineering Label
Switched Path (TE LSP) on a downstream Label Switch Router (LSR).
However, existing protocol mechanisms are not sufficient to find an MP
address in multi-domain routing networks where a domain is defined as
an IGP area or an Autonomous System. Hence, the current MPLS Fast
Reroute mechanism cannot be used to protect inter-domain TE LSPs from a
failure of an ABR (Area Border Router) or ASBR (Autonomous System
Border Router) respectively. This document specifies the use of
existing Route Record Object (RRO) IPv4 and IPv6 sub-objects (with a
new flag defined) thus defining the node-id subobject in order to solve
this issue. Note that the MPLS Fast reroute mechanism mentioned in this
document refers to the "Facility backup" MPLS TE Fast Reroute method.
Table of content
1. Terminology -----------------------------
2. Introduction ----------------------------
3. Signaling node-ids in RROs -------------
4. Finding Merge Point ---------------------
5. Security Considerations -----------------
6. IANA Consideration
7. Intellectual Property Considerations ----
8. Acknowledgments -------------------------
9. References
9.1 Normative references
9.2 Informative references
10. Authors' addresses
Conventions used in this document
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 RFC-2119 [i].
1. Terminology
Bypass Tunnel: an LSP that is used to protect a set of LSPs passing
over a common facility.
Backup Tunnel: the LSP that is used to backup up one of the many LSPs
in many-to-one backup.
CSPF: Constraint-based Shortest Path First.
Inter-area TE LSP: TE LSP whose head-end LSR and tail-end LSR do not
reside within the same IGP area or whose head-end LSR and tail-end LSR
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are both in the same IGP area although the TE-LSP transiting path may
be across different IGP areas.
Inter-AS MPLS TE LSP: TE LSP whose Head-end LSR and Tail-end LSR do not
reside within the same Autonomous System (AS) or both Head-end
LSR and Tail-end LSR are in the same AS but the TE tunnel transiting
path may be across different ASes
Interconnect or ASBR Routers: Routers used to connect to another AS of
a different or the same Service Provider via one or more Inter-AS
links.
LER: Label Edge Router.
LSDB: Link State Database.
LSP: An MPLS Label Switched Path
LSR: Label Switch Router
Local Repair: techniques used to repair LSP tunnels quickly when a node
or link along the LSPs path fails.
PCC: Path Computation Client: any client application requesting a path
computation to be performed by the Path Computation Element.
PCE: Path Computation Element: an entity (component, application or
network node) that is capable of computing a network path or route
based on a network graph and applying computational constraints (see
further description in section 3).
MP: Merge Point. The LSR where detour or backup tunnels meet the
protected LSP. In case of one-to-one backup, this is where multiple
detours converge. A MP may also be a PLR.
Protected LSP: an LSP is said to be protected at a given hop if it has
one or multiple associated backup tunnels originating at that hop.
PLR: Point of Local Repair. The head-end of a backup tunnel or a detour
LSP.
Reroutable LSP: Any LSP for with the "Local protection desired" bit is
set in the Flag field of the SESSION_ATTRIBUTE object of its Path
messages.
2. Introduction
MPLS Fast Reroute (FRR) ([FAST-REROUTE]) is a fast recovery local
protection technique used to protect Traffic Engineering LSPs from
link/SRLG/node failure. One or more backup tunnels are pre-established
to protect against the failure of a link/node/SRLG. In case of failure,
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every protected TE LSP traversing the failed resource is rerouted onto
the appropriate backup tunnels in tens of msecs.
There are several requirements on the backup tunnel path that must be
satisfied. First, the backup tunnel must not traverse the element that
it protects. Additionally, a primary tunnel and its associated backup
tunnel should intersect at least at two points (nodes): Point of Local
Repair (PLR) and Merge Point (MP). The former should be the head-end
LSR of the backup tunnel and the latter should be the tail-end LSR of
the backup tunnel. The PLR is where FRR is triggered when
link/node/SRLG failure happens.
There are different methods for computing paths for backup tunnels at a
given PLR. Specifically, a user can statically configure one or more
backup tunnels at the PLR with an explicitly configured path or the PLR
can be configured to automatically compute a backup path or to send a
path computation request to a PCE.
Consider the following scenario (figure 1)
Assumptions:
- A multi-area network made of three areas: 0, 1 and 2,
- A fast reroutable TE LSP T1 (TE LSP signaled with the "local
Protection desired" bit set in the SESSION-ATTRIBUTE object or the
FAST-REROUTE object) from R0 to R3,
- A backup tunnel B1 from R1 to R2, not traversing ABR1, and following
the R1-ABR3-R2 path.
- The PLR R1 reroutes any protected TE LSP traversing ABR1 onto the
backup tunnel B1 in case of ABR1's failure.
<--- area 1 --><---area 0---><---area 2--->
R0-----R1-ABR1--R2------ABR2--------R3
\ /
\ /
ABR3
Figure 1: Use of Fast Reroute to protect a TE LSP against an ABR
failure with MPLS Traffic Engineering Fast Reroute
When T1 is first signaled, the PLR R1 needs to dynamically select an
appropriate backup tunnel intersecting T1 on a downstream LSR. However,
existing protocol mechanisms are not sufficient to unambiguously find
the MP address in a network with inter-domain TE LSP. Note that
although the example above was given in the context of inter-area TE
LSPs, a similar reasoning applies to the case of inter-AS TE LSP. This
document addresses these limitations.
R1 needs to ensure the following:
1. The backup tunnel intersects with the primary tunnel at the MP
(and thus has a valid MP address). For the sake of illustration,
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in Figure 1, R1 needs to determine that T1 and B1 share the same
MP node R2.
2. The backup tunnel satisfies the primary LSP's request with
respect to the bandwidth protection request (i.e., bandwidth
guaranteed for the primary tunnel during failure), and the type
of protection (preferably, protecting against a node failure
versus a link failure), as specified in [FAST-REROUTE].
A PLR can make sure that condition (1) is met by examining the Record
Route Object (RRO) of the primary tunnel to see if any of the addresses
specified in the RRO is attached to the tail-end of the backup tunnel.
As per [RSVP-TE], the addresses specified in the RRO IPv4 or IPv6 sub-
objects sent in Resv messages can be node-ids and/or interface
addresses. Hence, in Figure 1, router R2 may specify interface
addresses in the RROs for T1 and B1. Note that these interface
addresses are different in this example.
The problem of finding the MP using the interface addresses or node-ids
can be easily solved in the case of a single IGP area. Specifically, in
the case of a single IGP area, the PLR has the knowledge of all the
interfaces attached to the tail-end of the backup tunnel. This
information is available in PLR's IGP topology database. Thus, the PLR
can unambiguously determine whether a backup tunnel intersecting a
protected TE LSP on a downstream node exists and can also find the MP
address regardless of how the addresses carried in the RRO IPv4 or IPv6
sub-objects are specified (i.e., whether using the interface addresses
or the node-ids). However, such routing information is not available in
the case of inter-domain environments. Hence, unambiguously making sure
that condition (1) above is met in the case of inter-domain TE LSPs is
not possible with existing mechanisms.
In this document, we define extensions to and describe the use of RSVP
[RSVP, RSVP-TE] to solve the above-mentioned problem. Note that the
requirement for the support of the fast recovery technique specified in
[FAST-REROUTE] to inter-domain TE LSPs has been specified in [INTER-
AREA-TE-REQS] and [INTER-AREA-TE-REQS].
2. Signaling node-ids in RROs
As mentioned above, the limitation that we need to address is the
generality of the contents of the RRO IPv4 and IPv6 sub-objects, as
defined in [RSVP-TE]. [RSVP-TE] defines the IPv4 and IPv6 RRO sub-
objects. Moreover, two additional flags are defined in [FAST-REROUTE]:
the "Local Protection Available" and "Local protection in use" bits.
In this document, we define the following new flag:
Node-id: 0x20
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When set, this indicates that the address specified in the
RRO's IPv4 or IPv6 subobject is a node-id address, which refers
to the "Router Address" as defined in [OSPF-TE], or "Traffic
Engineering Router ID" as defined in [ISIS-TE]. A node MUST use
the same address consistently. Once an address is used in RRO's
IPv4 or IPv6 subobject, it should always be used for the
lifetime of the LSP.
An IPv4 or IPv6 RRO subobject with the node-id flag set is also called
a node-id subobject. The problem of finding a MP address in a network
with inter-domain TE LSP is solved by inserting a node-id subobject (an
RRO "IPv4" and "IPv6" sub-object with the 0x20 flag set) in the RRO
object carried in the RSVP Resv message.
An implementation may either decide to:
1) Add the node-id subobject in an RSVP Resv message and, when
required, also add another IPv4/IPv6 subobject to record interface
address.
Example: an inter-domain fast reroutable TE LSP would have in the RRO
object carried in Resv message two sub-objects: a node-id subobject and
a label sub-object. If recording the interface address is required,
then an additional IPv4/IPv6 subobject is added.
2) Add an IPv4/IPv6 sub-object recording the interface address and,
when required, add a node-id subobject in the RRO object.
Example: an inter-domain fast reroutable TE LSP would have in the RRO
object carried in Resv message three sub-objects: an IPv4/IPv6 sub-
object recording interface address, a label sub-object and a node-id
sub-object.
Note also that the node-id sub-object may have other application than
Fast Reroute backup tunnel selection. Moreover, it is RECOMMENDED that
an LSR recording a node-id address in an IPv4/IPv6 RRO sub-object also
set the Node-id flag.
3. Finding Merge Point
Two cases should be considered:
- Case 1: the backup tunnel destination is the MP's node-id. Then a PLR
can find the MP and suitable backup tunnel by simply comparing the
backup tunnel's destination address with the node-id included in the
RRO of the primary tunnel.
- Case 2: the backup tunnel terminates at an address different than the
MP's node-id. Then a node-id subobject MUST also be included in the RRO
object of the backup tunnel. A PLR can find the MP and suitable backup
tunnel by simply comparing the node-ids present in the RRO objects of
both the primary and backup tunnels.
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When both IPv4 node-id and IPv6 node-id sub-objects are present, a PLR
may use any or both of them in finding the MP address.
4. Security Considerations
This document does not introduce new security issues. The security
considerations pertaining to [RSVP] and [RSVP-TE] remain relevant.
5. IANA considerations
IANA will assign a new flag in the RRO object defined in [RSVP-TE]:
Node-id flag: 0x20 (to be assigned by IANA).
6. Intellectual Property Considerations
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights 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; nor does it represent that it has made
any independent effort to identify any such rights. Information on the
procedures with respect to rights in RFC documents can be found in BCP
78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this specification
can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary rights
that may cover technology that may be required to implement this
standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
7. Acknowledgments
We would like to acknowledge input and helpful comments from Carol
Iturralde, Anca Zamfir, Reshad Rahman, Rob Goguen, Philip Matthews and
Adrian Farrel.
8. References
8.1 Normative References
[RFC2119]Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC3667]Bradner, S., "IETF Rights in Contributions", BCP 78, RFC 3667,
February 2004.
[RFC3668]Bradner, S., Ed., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3668, February 2004.
[RSVP] Braden, et al, "Resource ReSerVation Protocol (RSVP) - Version
1, Functional Specification", RFC 2205, September 1997.
[RSVP-TE] Awduche, et al, "Extensions to RSVP for LSP Tunnels", RFC
3209, December 2001.
[FAST-REROUTE] Ping Pan, et al, "Fast Reroute Extensions to RSVP-TE for
LSP Tunnels", draft-ietf-mpls-rsvp-lsp-fastreroute-07.txt. Work in
progress.
[OSPF-TE] Katz et al., "Traffic Engineering (TE) Extensions to OSPF
Version 2", RFC3630.
[ISIS-TE] Smit et al., "Intermediate System to Intermediate System (IS-
IS) - Extensions for Traffic Engineering (TE)IS-IS extensions for
Traffic Engineering", RFC3784.
8.2 Informative references
[INTER-AREA-TE-REQS] Le Roux, Vasseur, Boyle et al., "Requirements for
Inter-Area MPLS Traffic Engineering", draft-ietf-tewg-interarea-mpls-te-
req-03.txt. Work in progress.
[INTER-AS-TE-REQS] Zhang, Vasseur et al, "MPLS Inter-AS Traffic
Engineering requirements", draft-tewg-interas-te-req-09.txt. Work in
progress.
9. Authors' Addresses
Jean-Philippe Vasseur
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough , MA - 01719
USA
Email: jpv@cisco.com
Zafar Ali
Cisco Systems, Inc.
100 South Main St. #200
Ann Arbor, MI 48104
USA
zali@cisco.com
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draft-ietf-mpls-nodeid-subobject-06.txt May 2005
Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario, K2K 3E8
Canada
msiva@cisco.com
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Vasseur, Ali and Sivabalan 9