draft-ietf-mpls-nodeid-subobject-01.txt May 2003
Jean Philippe Vasseur
Zafar Ali
Siva Sivabalan
Cisco Systems, Inc.
IETF Internet Draft
Expires: November, 2003
May, 2003
draft-ietf-mpls-nodeid-subobject-01.txt
Definition of an RRO node-id subobject
Status of this Memo
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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 fast reroutable Traffic
Engineering LSP on a downstream LSR. However, existing protocol
mechanisms are not sufficient to find an MP address in multi-areas or
multi-domain routing networks. 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. Note that
the MPLS Fast reroute mechanism mentioned in this draft refers to the
"Facility backup" MPLS TE Fast Reroute method.
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.
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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.
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 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.
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, 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 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 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).
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Consider the following scenario:
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 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
the 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 or IPv6
subobjects 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 a single area (OSPF_)/level (IS-IS).
Specifically, in the case of single area/level, 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
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protected TE LSP on a downstream node exists and can also find the MP
address regardless of how the 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 multi-area and inter-AS trafficengineering 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
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along the protected LSP. The PLR may set this whenever node
protection is provided by the protected LSP's backup path; the
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.
Preemption pending: 0x10
The preempting node sets this flag if a pending preemption is
in progress for the TE LSP. This indicates to the HE of this
LSP that it must be re-routed as soon as possible using a make
before break.
In this document, we define the following new flag:
Node-id: 0x20
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. In other words, 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-area or inter-AS traffic engineering is solved by inserting
a node-id subobject (an RRO "IPv4" and "IPv6" sub-object with the 0x20
flag set).
An implementation MAY either decide to support of one the following
options:
Option 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: a fast reroutable TE LSP would have in the RRO object carried
in Resv message two subobjects: a node-id subobject and a label
subobject. If recording the interface address is required, then an
additional IPv4/IPv6 subobject is added.
Option 2: add an IPv4/IPv6 subobject recording the interface address
and, when required, add a node-id subobject in the RRO object.
Example: an inter-area/inter-AS fast reroutable TE LSP would have in
the RRO object carried in Resv message three subobjects: an IPv4/IPv6
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subobject recording interface address, a label subobject and a node-id
subobject.
Note also, that the node-id subobject may have other application than
Fast Reroute backup tunnel selection.
4. 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.
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.
5. Security Considerations
This document does not introduce new security issues. The security
considerations pertaining to the original RSVP protocol [RSVP] remain
relevant.
6. Intellectual Property Considerations
Cisco Systems may have intellectual property rights claimed in regard
to some of the specification contained in this document
7. Acknowledgments
We would like to acknowledge input and helpful comments from Carol
Iturralde, Anca Zamfir, Reshad Rahman, Rob Goguen and Philip Matthews.
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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[FAST-REROUTE] Ping Pan, et al, "Fast Reroute Extensions to RSVP-TE for
LSP Tunnels", draft-ietf-mpls-rsvp-lsp-fastreroute-02.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-
01.txt, February 2003, Work in Progress.
[INTER-AS-TE-REQS] Zhang et al, "MPLS Inter-AS Traffic Engineering
requirements", draft-tewg-interas-te-req-02.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 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
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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