One document matched: draft-ietf-mpls-nodeid-subobject-00.txt
draft-ietf-mpls-nodeid-subobject-00.txt February 2003
Jean Philippe Vasseur
Zafar Ali
Siva Sivabalan
Cisco Systems, Inc.
IETF Internet Draft
Expires: August, 2003
February, 2003
draft-ietf-mpls-nodeid-subobject-00.txt
Definition of an RRO node-id subobject
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 Task Force (IETF), its
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Vasseur, Ali and Sivabalan 1
draft-ietf-mpls-nodeid-subobject-00.txt February 2003
Abstract
In the context of MPLS TE Fast Reroute ([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 protected Traffic
Engineering LSP on a downstream LSR. However, existing protocol
mechanisms are not sufficient to find MP address multi-areas or multi-
domain routing network. Hence, the current MPLS Fast Reroute mechanism
cannot be used to protect inter-area or inter-AS 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 RRO
IPv4 and IPv6 subobjects (with a new flag defined) to define the node-
id subobject in order to solve this issue.
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
LSR - Label Switch Router
LSP - An MPLS Label Switched Path
PCS - Path Computation Server (may be any kind of LSR (ABR, ...)
or a centralized path computation server
PCC - Path Computation Client (any head-end LSR) requesting a path
computation of the Path Computation Server.
Local Repair - Techniques used to repair LSP tunnels quickly
when a node or link along the LSPs path fails.
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.
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.
PLR - Point of Local Repair. The head-end of a backup tunnel or
a detour LSP.
MP - Merge Point. The LSR where detour or backup tunnels meet
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the protected LSP. In case of one-to-one backup, this is where
multiple detours converge. A MP may also be a PLR.
NHOP Bypass Tunnel - Next-Hop Bypass Tunnel. A backup tunnel
which bypasses a single link of the protected LSP.
NNHOP Bypass Tunnel - Next-Next-Hop Bypass Tunnel. A backup
tunnel which bypasses a single node of the protected 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.
CSPF - Constraint-based Shortest Path First.
Inter-AS MPLS TE: 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.
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 TE LSPs (called backup LSPs) are
pre-established to protect against the failure of a link/node/SRLG. In
case of failure, every protected TE LSP traversing the failed resource
is rerouted onto the appropriate backup tunnels in 10s of msecs.
There are a couple of requirements on the backup tunnel path. At least,
a backup tunnel should not pass through the element it protects.
Additionally, a primary tunnel and a 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.
Furthermore, the MP address is also required to send RSVP Refresh
messages of the rerouted TE LSPs when the FRR is active.
There are different methods for computing paths for backup tunnels.
Specifically, a users can statically configures one or more backup
tunnels at the PLR, with explicit path or the PLR can be configured to
automatically compute a backup path or to send a path computation
request to a PCS (which can be an LSR or an off-line tool).
Consider the following scenario
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Asumptions:
- a multi-area network made of three areas: 0, 1 and 2.
- a protected TE LSP T1 (TE LSP signaled with the "local Protection
desired" bit set in the SESSION-ATTRIBUTE object or the FRR object)
from R0 to R3
- a backup tunnel B1 from R1 to R2, not traversing ABR1, and following
the R1-ABR3-R2 path. 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 /
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
MP address in a network with inter-area or inter-AS traffic engineering
(although the example above was given in the context of multi-area
networks, a similar reasoning applies to TE LSP spanning multiple
ASes). This draft addresses these limitations.
R1 needs to ensure the following:
1. Backup tunnel intersects with the primary tunnel at the MP (and
thus has a valid MP address), e.g., in Figure 1, R1 needs to
determine that T1 and B1 share the same MP node R2,
2. 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 subobjects
can be node-ids and/or interface addresses, with specific
recommendation to use the interface address of the outgoing Path
messages. Hence, in Figure 1, router R2 is more likely to 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 a single area TE. Specifically, in the case of
single area TE, 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 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
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addresses contained in the RRO IPv4 or IPv6 subobjects are specified
(i.e., whether using the interface addresses or the node IDs). However,
such routing information is not available in a multi-area and inter-AS
traffic-engineering environments. Hence, unambiguously making sure that
condition (1) above is met with inter-area TE and inter-AS traffic-
engineering TE LSPs is not possible with existing mechanisms.
In this draft, we define extensions to and describe the use of RSVP
[RSVP, RSVP-TE] to solve the above-mentioned problem.
3. 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 subobjects, as
defined in [RSVP-TE].
The IPv4 and IPv6 RRO subobjects are currently defined in [RSVP-TE] and
have the following flags defined:
Local protection available: 0x01
Indicates that the link downstream of this node is protected
via a local repair mechanism, which can be either one-to-one
or facility backup.
Local protection in use: 0x02
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, or an outage of the neighboring
node).
Bandwidth protection: 0x04
The PLR will set this when the protected LSP has a backup path
which is guaranteed to provide the desired bandwidth specified
in the FAST_REROUTE object or the bandwidth of the protected
LSP, if no FAST_REROUTE object was included. The PLR may set
this whenever the desired bandwidth is guaranteed; the PLR
MUST set this flag when the desired bandwidth is guaranteed
and the "bandwidth protection desired" flag was set in the
SESSION_ATTRIBUTE object. If the requested bandwidth is not
guaranteed, the PLR MUST NOT set this flag.
Node protection: 0x08
The PLR will set this when the protected LSP has a backup path
which provides protection against a failure of the next LSR
along the protected LSP. The PLR may set this whenever node
protection is provided by the protected LSP's backup path; the
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PLR MUST set this flag when the node protection is provided
and the "node protection desired" flag was set in the
SESSION_ATTRIBUTE object. If node protection is not provided,
the PLR MUST NOT set this flag. Thus, if a PLR could only
setup a link-protection backup path, the "Local protection
available" bit will be set but the "Node protection" bit will
be cleared.
An additional flag is specified:
Node-id: 0x10
When set, this indicates that the address specified in the RRO
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.
An IPv4 or IPv6 RRO subobject with the node-is flag set is also called
a node-id subobject.
The problem of finding MP address in a network with inter-area or
inter-AS traffic engineering is solved by adding a node-id subobject
(an RRO "IPv4" and "IPv6" sub-object with the 0x10 flag set).
Any Head-end LSR of a protected TE LSP MUST include an RRO object, as
defined in [FAST-REROUTE]. In addition, any LSR compliant with this
draft must systematically include a node-id IPv4 or IPv6 subobject in
the RRO object for each protected TE LSP (in addition to the sub-
objects required by MPLS TE Fast Reroute as defined in [FAST-REROUTE]).
A node MAY decide to include its node-id subobject in the RRO object
only for the TE LSP whose IPv4 or IPv6 address source address
(specified in the SENDER-TEMPLATE object of the RSVP Path message) does
not belong to its local area/AS.
4. Processing RRO with node-id subobjects
The node-id subobject is added into the RECORD_ROUTE object after the
Label Record subobject. A node MUST not push a node-id subobject
without also pushing an IPv4 or IPv6 subobjects, as defined in [FAST-
REROUTE]. A node may push both IPv4 node-id and IPv6 node-id sub-
objects, but that MUST be done on consistent basis.
4.1. Finding Merge Point
A PLR can find the MP and suitable backup tunnel by simply comparing
the node-id of the backup tunnel's tail-end with Node IDs included in
the RRO of the primary tunnel. When both IPv4 node-id and IPv6 node-id
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sub-objects are present, a PLR may use any or both of them in finding
the MP address.
4.2. Processing at the border nodes
In a network with inter-AS traffic engineering, there may be some
concerns about leaking the RRO information, including node-id
subobjects, outside the autonomous system (see [INTER-AS-TE-REQS]). In
such cases, before forwarding the RRO object outside of an AS, the ASBR
may filter some/all node-id subobjects pertaining to the downstream
nodes in the AS. The RRO node-id subobjects filtration can be based on
a local policy configured on the ASBR.
How an ASBR handles/filters the contents of the RRO objects is outside
of the scope of this draft.
5. Backward Compatibility Note
To remain compatible with the nodes that do not support the RRO IPv4 or
IPv6 node-id subobjects, a node can safely ignore these objects. The
implication of this limitation will be that these nodes could not be MP
in a network with inter-area or inter-AS traffic engineering.
6. Security Considerations
This document does not introduce new security issues. The security
considerations pertaining to the original RSVP protocol [RSVP] remain
relevant.
7. Intellectual Property Considerations
Cisco Systems may have intellectual property rights claimed in regard
to some of the specification contained in this document
8. Acknowledgments
We would like to acknowledge input and helpful comments from Carol
Iturralde, Anca Zamfir, and Reshad Rahman.
References
[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.
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draft-ietf-mpls-nodeid-subobject-00.txt February 2003
[FAST-REROUTE] Ping Pan, et al, "Fast Reroute Extensions to RSVP-TE for
LSP Tunnels", draft-ietf-mpls-rsvp-lsp-fastreroute-01.txt, May 2003.
[OSPF-TE] Katz, D., Yeung, D., Kompella, K., "Traffic Engineering
Extensions to OSPF Version 2", draft-katz-yeung-ospf-traffic-
09.txt(work in progress).
[ISIS-TE] Li, T., Smit, H., "IS-IS extensions for Traffic Engineering",
draft-ietf-isis-traffic-04.txt (work in progress)
[MULTI-AREA-TE] Kompella at all,"Multi-area MPLS Traffic Engineering",
draft-kompella-mpls-multiarea-te-03.txt, June 2002.
[LOOSE-PATH-REOPT] Vasseur and Ikejiri, "Reoptimization of an explicit
loosely routed MPLS TE paths", draft-vasseur-mpls-loose-path-reopt-
00.txt, February 2003, Work in Progress.
[ABR-ASBR-FRR] Vasseur, Ali and Sivabalan, "Support of MPLS TE Fast
Reroute protection of ABR/ASBR LSRs", draft-vasseur-mpls-abr-asbr-frr
00.txt, February 2003, Work in progress.
[INTER-AS-TE-REQS] Zhang et al, "MPLS Inter-AS Traffic Engineering
requirements", draft-tewg-interas-te-req-01.txt (work in progress).
[INTER-AS-TE] Vasseur and Zhang, "MPLS Inter-AS Traffic Engineering",
draft-vasseur-mpls-inter-as-te-00.txt, February 2003, work in progress.
Authors' Address:
Jean Philippe Vasseur
Cisco Systems, Inc.
300 Apollo Drive
Chelmsford, MA 01824
USA
Email: jpv@cisco.com
Zafar Ali
Cisco Systems, Inc.
100 South Main St. #200
Ann Arbor, MI 48104
USA
zali@cisco.com
Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario, K2K 3E8
Canada
msiva@cisco.com
Vasseur, Ali and Sivabalan 8
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