IETF Internet Draft Arthi Ayyangar(Editor)
Proposed Status: Standards Track Juniper Networks
Expires: April 2005
Jean-Philippe Vasseur(Editor)
Cisco Systems, Inc.
October 2004
Inter domain GMPLS Traffic Engineering - RSVP-TE extensions
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt
Status of this Memo
This document is an Internet-Draft and is subject to all provisions of
section 3 of RFC 3667. By submitting this Internet-Draft, each author
represents that any applicable patent or other IPR claims of which he or
she is aware have been or will be disclosed, and any of which he or she
become aware will be disclosed, in accordance with RFC 3668.
Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups. Note that other groups
may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as ``work in progress.''
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document describes extensions to Generalized Multi-Protocol Label
Switching (GMPLS) Resource ReserVation Protocol - Traffic Engineering
(RSVP-TE) signaling required to support mechanisms for the establishment
and maintenance of GMPLS Traffic Engineering (TE) Label Switched Paths
(LSPs), both packet and non-packet, that traverse multiple domains. For
the purpose of this document, a domain is considered to be any
collection of network elements within a common realm of address space or
Ayyangar and Vasseur [Page 1]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
path computation responsibility. Examples of such domains include
Autonomous Systems, IGP areas and GMPLS overlay networks.
1. Introduction
The requirements for inter-area and inter-AS MPLS Traffic Engineering
have been developed by the Traffic Engineering Working Group and have
been stated in [INTER-AREA-TE-REQS] and [INTER-AS-TE-REQS]
respectively. Many of these requirements also apply to GMPLS
networks. The framework for inter-domain GMPLS Traffic Engineering
has been provided in [INTER-DOMAIN-FRAMEWORK].
This document presents the RSVP-TE signaling extensions for the setup
and maintenance of TE LSPs that span multiple domains. The signaling
procedures described in this document are applicable to both packet
LSPs ([RSVP-TE]) and non-packet LSPs that use RSVP-TE GMPLS
extensions as described in [RSVP-GMPLS]. Three different signaling
methods along with the corresponding RSVP-TE extensions and
procedures are proposed in this document.
For the purpose of this document, a domain is considered to be any
collection of network elements within a common realm of address space
or path computation responsibility. Examples of such domains include
Autonomous Systems, IGP areas and GMPLS overlay networks ([GMPLS-
OVERLAY]).
1.1. 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 [RFC2119].
1.2. Terminology
ASBR: routers used to connect together ASes of a different or the
same Service Provider via one or more Inter-AS links.
Bypass Tunnel: an LSP that is used to protect a set of LSPs passing
over a common facility.
ERO: Explicit Route Object
FA: Forwarding Adjacency
FA-LSP: Forwarding Adjacency LSP
LSP: MPLS Label Switched Path
Ayyangar and Vasseur [Page 2]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
MP: Merge Point. The node where bypass tunnels meet the protected
LSP.
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.
PLR: Point of Local Repair. The head-end of a bypass tunnel.
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.
RRO - Record Route Object
TE: Traffic Engineering
TE LSP: Traffic Engineering Label Switched Path
TE-link: Traffic Engineering link
TED: MPLS Traffic Engineering Database
2. Signaling overview
The RSVP-TE signaling of a TE LSP within a single domain is described
in [RSVP-TE] and [RSVP-GMPLS]. This document focuses on the RSVP-TE
signaling extensions required for inter-domain TE LSP setup and
maintenance. Any other extensions that may be needed for routing or
path computation are outside the scope of this document.
2.1. Signaling options
There are three ways in which an RSVP-TE LSP could be signaled across
multiple domains:
Contiguous - A contiguous TE LSP is a single end-to-end TE LSP that
is setup across multiple domains using RSVP-TE signaling procedures
described in [RSVP-TE]and [RSVP-GMPLS]. No additional TE LSPs are
required to signal a contiguous TE LSP and the same RSVP-TE
information for the TE LSP is maintained along the entire LSP path.
Nesting - Nesting one or more TE LSPs into another TE LSP is
described in [LSP-HIERARCHY]. This technique can also be used to nest
one or more inter-domain TE LSPs into an intra-domain FA-LSP. While
Ayyangar and Vasseur [Page 3]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
similar to stitching in the control plane, in the data plane, nesting
allows for one or more inter-domain LSPs to be transported over a
single intra-domain FA-LSP using the label stacking construct.
Stitching - A stitched TE LSP is a TE LSP made up of different TE LSP
segments within each domain which are "stitched" together in the data
plane so that an end-to-end LSP is achieved in the data plane. In the
control plane, however, the different LSP segments are signaled as
distinct RSVP sessions which are independent from the RSVP session
for the inter-domain LSP. Signaling procedures described in [LSP-
HIERARCHY] are used to stitch an inter-domain TE LSP to a local LSP
segment. The concept of LSP stitching and additional signaling
extensions needed are described in detail in the following section.
On receipt of an LSP setup request for an inter-domain TE LSP, the
decision of whether to signal the LSP contiguously or whether to nest
or stitch it to another TE LSP, depends on the signaled TE LSP
characteristics or the local node configuration, when not explicitly
signaled. Also, the TE LSP segment or FA-LSP within the domain may
either be pre-configured or signaled dynamically based on the arrival
of the inter-domain TE LSP setup request.
3. LSP Stitching
LSP stitching is a special case of LSP hierarchy ([LSP-HIERARCHY])
where the desired switching type of the LSP and the switching
capability of the LSP segment are such that exactly one LSP may be
admitted into an LSP segment. E.g. an inter-domain lambda LSP may be
stitched into an intra-domain lambda LSP, an MPLS LSP (PSC) can be
stitched into another MPLS LSP (PSC). The following sections analyze
the similarities and differences of various aspects associated with
nesting and stitching and describe additional signaling extensions
required for LSP stitching.
3.1. Routing aspects
An LSP segment is similar to an FA-LSP in that an LSP segment like an
FA-LSP is created and treated like a Traffic Engineering link (TE-
link) between two GMPLS nodes whose path transits zero or more GMPLS
nodes in the same instance of the GMPLS control plane. These TE-links
may be numbered or unnumbered. For an unnumbered LSP segment, the
assignment and handling of the local and remote link identifiers is
specified in [RSVP-UNNUM]. Like in the case of Forwarding Adjacency
(FA), a routing adjacency will not usually be established over an LSP
segment. ISIS/OSPF would, however, flood the TE information
associated with an LSP segment which will exist in the TE database
(TED) and can be used for path computation. The TE parameters defined
Ayyangar and Vasseur [Page 4]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
for an FA in [LSP-HIERARCHY] are also applicable to an LSP segment
TE-link.
Note that, while an FA-LSP TE-link can admit one or more LSPs over
it, an LSP segment can admit exactly one LSP over it. So, once an LSP
is stitched into an LSP segment, the Unreserved bandwidth on the LSP
segment is set to and advertised to be zero. This prevents any more
LSPs from being computed and admitted over the LSP segment TE-link.
Multiple LSP segments between the same pair of nodes may be bundled
using the concept of Link Bundling ([BUNDLING]) into a single TE-
link. When any component LSP segment is allocated for an LSP, its
Unreserved bandwidth MUST be set to zero and the Minimum and Maximum
LSP bandwidth of the TE-link SHOULD be recalculated.
3.2. Signaling aspects
Like any TE-link or FA, a signaling adjacency would be established
between the end nodes of the LSP segment and this will be used to
signal an LSP over the LSP segment. When an RSVP-TE LSP is signaled
over an LSP segment, the Path message MUST contain an IF_ID RSVP_HOP
object [RSVP-GMPLS] and the data interface identification MUST
identify the LSP segment. For the purpose of ERO and RRO as well, an
LSP segment is treated exactly like an FA.
The main difference between signaling an LSP over an LSP segment
instead of over an FA-LSP is that no Labels are allocated and
exchanged for the end-to-end LSP (inter-domain LSP) over the LSP
segment hop. So, exactly one end-to-end LSP is associated with one
LSP segment. If a node at the head-end of an LSP segment receives a
Path Msg for an LSP that identifies the LSP segment in the ERO and
the LSP segment bandwidth has already been allocated to some other
LSP, then regular rules of RSVP-TE pre-emption apply. If the LSP
request over the LSP segment cannot be satisfied, then the node
SHOULD send back a PathErr with the error codes as described in
[RSVP-TE].
Additional signaling extensions for stitching are described in the
next section.
3.3. RSVP-TE signaling extensions
The signaling extensions described here MUST be used if a packet LSP
is being stitched to another packet LSP. These extensions are
optional for non-packet LSPs and SHOULD be used if no other local
mechanisms exist to automatically detect a requirement for stitching
at both the ingress and egress nodes of the LSP segment. Also, these
extensions are applicable to the local LSP segment and not for the
inter-domain TE LSP.
Ayyangar and Vasseur [Page 5]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
If a domain boundary node (or any other node) desires to perform LSP
stitching of an LSP, then it MUST indicate this in the Path message
for the intra-domain LSP segment. This signaling explicitly informs
the egress node for the LSP segment that the ingress node is planning
to perform stitching over the LSP segment. This will allow the egress
of the LSP segment to allocate the correct label(s) as explained
below. Also, so that the head-end node can ensure that correct
stitching actions were carried out at the egress node, a new flag is
defined below in the RRO subobject to indicate that the LSP segment
can be used for stitching.
In order to request LSP stitching on the LSP segment, we define a new
flag bit in the Attributes Flags TLV of the LSP_ATTRIBUTES object
defined in [LSP-ATTRIBUTES]:
0x02 (TBD): LSP stitching desired bit - This flag will be set in the
Attributes Flags TLV of the LSP_ATTRIBUTES object in the Path message
for the local intra-domain LSP segment by the head-end node of the
LSP segment (boundary node) that desires LSP stitching. This flag
MUST not be modified by any other nodes in that domain.
An intra-domain LSP segment can only be used for stitching if
appropriate label actions were carried out at the egress node of the
LSP segment. In order to indicate this to the head-end node of the
LSP segment, the following new flag bit is defined in the RRO
Attributes sub-object: 0x02 (TBD): LSP segment stitching ready.
If an egress node receiving a Path message, supports the
LSP_ATTRIBUTES object and the Attributes Flags TLV, and also
recognizes the "LSP stitching desired" flag bit, but cannot support
the requested stitching behavior, then it MUST send back a PathErr
message with an error code of "Routing Problem" and an error sub-
code=16 (TBD) "Stitching unsupported" to the head-end node of the
intra-domain LSP segment.
If an egress node receiving a Path message with the "LSP stitching
desired" flag set, recognizes the object, the TLV and the flag and
also supports the desired stitching behavior, then it MUST allocate a
non-NULL label for that LSP segment in the corresponding Resv
message. Now, so that the head-end node can ensure that the correct
label actions will be carried out by the egress node and that the LSP
segment can be used for stitching, the egress node MUST set the "LSP
segment stitching ready" bit defined in the RRO Attribute sub-object.
Also, when the egress node for the LSP segment receives a Path
message for an inter-domain LSP using this LSP segment, it SHOULD
first check if it is also the egress for the inter-domain TE LSP. If
the egress node is the egress for both the intra-domain LSP segment
as well as the inter-domain TE LSP, and this is a packet LSP which
Ayyangar and Vasseur [Page 6]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
requires Penultimate Hop Popping (PHP), then the node MUST send back
a Resv refresh for the intra-domain LSP segment with a new label
corresponding to the NULL label.
Finally, if the egress node for the intra-domain LSP segment supports
the LSP_ATTRIBUTES object but does not recognize the Attributes Flags
TLV, or supports the TLV as well but does not recognize this
particular flag bit, then it SHOULD simply ignore the above request.
An ingress node requesting stitching MUST examine the RRO Attributes
sub-object flag corresponding to the egress node for the intra-domain
LSP segment, to make sure that stitching actions were carried out at
the egress node. It MUST NOT use the LSP segment for stitching if the
"LSP segment stitching ready" flag is cleared.
The egress node MUST not allocate any Label in the Resv message for
the inter-domain TE LSP. Similarly, in case of bidirectional inter-
domain TE LSP, no Upstream Label is allocated over the LSP segment in
the corresponding Path message. An ingress node stitching an inter-
domain LSP to an LSP segment MUST ignore any Label object received in
the Resv for the inter-domain TE LSP.
4. Procedures on the domain boundary node
Whether an inter-domain TE LSP is contiguous, nested or stitched is
determined mostly by the signaling method supported by or configured
on the intermediate nodes, usually the domain boundary nodes that the
inter-domain TE LSP traverses through. It may also depend on certain
parameters signaled by the head-end node for the inter-domain TE LSP.
When a domain boundary node receives the RSVP Path message for an
inter-domain TE LSP setup, it MUST carry out the following procedures
before it can forward the Path message to the next hop node,
- apply any locally configured policies
- determine the signaling method to be used based on any desired
characteristics signaled by the head-end node of the inter-domain TE
LSP or if the signaling method is not explicitly signaled, then
determine the signaling method based on local configuration and
policies
- depending on the signaling method, carry out any specific ERO
procedures, as applicable, as described in the next section
- based on the signaling method to be used, determine the next
hop node to forward the RSVP Path message
- in case of nesting or stitching, either find an existing intra-
domain TE LSP to carry the inter-domain TE LSP or signal a new one,
depending on local policy
- perform any path computations if required. The path computation
Ayyangar and Vasseur [Page 7]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
procedure itself is outside the scope of this document. The various
path computation options are addressed in [INTER-DOMAIN-PATH-COMP]
- in case of any failures (admission control, policy, signaling;
etc), originate corresponding error notifications
4.1. Rules on ERO processing
The ERO that a domain boundary node receives in the Path message for
an inter-domain TE LSP will be dependent on several factors such as
the level of visibility that the head-end node of the inter-domain TE
LSP has into other domains, the path computation techniques applied
at the head-end node, policy agreements between two domains; etc.
Eventually, when the ERO reaches a domain boundary node, the
following rules SHOULD be used for ERO processing and signaling.
Within a domain, there may be no FA-LSPs or LSP segments. If they are
present, then they may originate and terminate on domain boundary
nodes. There could also be FA-LSPs and LSP segments that may
originate and terminate at other nodes in the domain. In general,
these ERO processing rules are also applicable to non-boundary nodes
that may participate in signaling the inter-domain TE LSP.
- If there are any policies related to ERO processing for
certain LSPs, they SHOULD be applied and corresponding actions should
be taken. E.g. if there exists a policy to reject LSP setup request
containing ERO with sub-objects identifying nodes within the domain,
then a PathErr with the appropriate error code should be sent back
- Section 8.2 of [LSP-HIERARCHY] describes how a node at the
edge of a region (domain) processes the ERO in the incoming Path
message and uses this ERO, to either find an existing FA-LSP or
signal a new FA-LSP using the ERO hops. This also includes adjusting
the ERO before sending the Path message to the next hop node. These
procedures SHOULD also be followed for nesting or stitching of inter-
domain TE LSPs to FA-LSPs or LSP segments respectively. While the
domain boundaries are tied to link switching capabilities in [LSP-
HIERARCHY], these procedures are also applicable to other domain
boundary nodes in the context of this document. E.g. in case of a
path computation domain, you have reached the boundary when the ERO
hop is no longer reachable via the TE database (TED).
- In case of any failure in processing the ERO hop(s), a Path
Error message with appropriate error code ([RSVP-TE]) SHOULD be
generated.
4.2. LSP setup failure and crankback
In case of any setup failures along the path due to policy or
admission control or other reasons, a corresponding Path Error SHOULD
be generated and sent upstream. The propagation of Path Error
upstream may be limited to within the domain or it may be sent all
the way upstream to the head-end node of the inter-domain TE LSP.
Ayyangar and Vasseur [Page 8]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
This depends not only on local configuration and ability of a
boundary node to do local crankback, but also on any specific
parameters requested by the head-end node itself for that LSP. In
certain cases, it may be desirable for the head-end node to exert
some control on the ability for the boundary nodes to make use of
crankback. See [CRANKBACK] for the definition of those bits. When
crankback is allowed, the domain boundary node can either decide to
forward the Path Error message upstream to the head-end node of the
inter-domain TE LSP or try to select another egress boundary node.
When crankback is not allowed or if the node has not been configured
to do a crankback, then a boundary node, when receiving a Path Error
message from a downstream boundary node MUST propagate the Path Error
message up to the head-end node of the inter-domain TE LSP.
5. RSVP-TE signaling extensions
The following RSVP-TE signaling extensions are introduced in this
document.
5.1. Control of downstream choice of signaling method
In certain mixed environments with different techniques (contiguous,
stitched or nested TE LSPs), a head-end node of the inter-domain TE
LSP may wish to signal its requirement regarding the signaling method
used at the domain boundaries.
[LSP-ATTRIBUTES] defines the format of the Attributes Flags TLV
included in the LSP_ATTRIBUTES object carried in an RSVP Path
message. The following bit in the Flags TLV is used by the head-end
node of the inter-domain TE LSP to restrict the signaling method used
by the domain boundary nodes to be contiguous.
0x01 (TBD): Contiguous LSP bit - this flag is set by the head-end
node that originates the inter-domain TE LSP if it desires a
contiguous end-to-end TE LSP (in the control & data plane). When set,
this indicates that a boundary node MUST not perform any stitching or
nesting on the TE LSP and the TE LSP MUST be routed as any other TE
LSP (it must be contiguous end to end). When this bit is cleared, a
boundary node may decide to perform stitching or nesting. A mid-point
node not supporting contiguous TE LSP MUST send a Path Error message
upstream with an error code of "Routing Problem" and error sub-
code=17 (TBD) (Contiguous LSP type not supported). This bit MUST not
be modified by any downstream node.
Ayyangar and Vasseur [Page 9]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
5.2. LSP stitching
RSVP-TE signaling extensions for LSP stitching have been described in
section 3. A new flag bit, "LSP stitching desired bit" is defined in
the Attributes Flags TLV of the LSP_ATTRIBUTES object defined in
[LSP-ATTRIBUTES], to request stitching over the LSP segment.
6. Example
6.1. Example topology
In this document, we will consider the following example topology for
inter-domain TE LSPs setup and maintenance. In this example, a domain
is an Autonomous system (AS).
<-- AS-1 ---> <--- AS-2 ---> <-- AS-3 -->
<---BGP---> <---BGP-->
CE1---R0----X1-ASBR1-----ASBR4--R3---ASBR7----ASBR9----R6
| | | | / | / | / | | |
| | +-ASBR2----/ ASBR5 | / | | |
| | | | | / | | |
R1--R2----ASBR3------ASBR6--R4---ASBR8----ASBR10----R7---CE2
<================ Inter-AS TE LSP ================>
6.1.1. Assumptions
- Three interconnected ASes, respectively AS1, AS2, and AS3. Note
that AS3 might be AS1 in some scenarios described in [INTER-AS-TE-
REQS].
- The various ASBRs are BGP peers, without any IGP running on the
single hop link interconnecting the ASBRs
- Each AS runs an IGP (IS-IS or OSPF) with the required IGP TE
extensions (see [OSPF-TE] and [ISIS-TE]). In other words, the ASes
are TE enabled. Note that each AS can run a different IGP.
- Each AS can be made of several areas. In this case, the TE LSP will
rely on the inter-area TE techniques to compute and set up a TE LSP
traversing multiple IGP areas. For the sake of simplicity, each
routing domain will be considered as single area in this document,
but the solutions described in this document does not prevent the use
of multi-area techniques. In fact, these inter-domain solutions are
equally applicable to inter-area TE.
Ayyangar and Vasseur [Page 10]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
- A protected inter-AS TE LSP T1 originated at R0 in AS1 and
terminating at R6 in AS3 with following possible paths:
LSP hops: R0-X1-ASBR1-ASBR4-R3-ASBR7-ASBR9-R6
o p1 - a set of loose node hops crossing AS-2
R0-X1-ASBR1(loose)-ASBR4(loose)-ASBR7(loose)-ASBR9(loose)-R6
o p2 - a set of strict interface hops crossing AS-2
R0-X1-ASBR1(loose)-link[ASBR1-ASBR4](strict)-link[ASBR4-R3](strict)
-link[R3-ASBR7](strict)-link[ASBR7-ASBR9](strict)-R6
- A set of backup tunnels:
o B1 from ASBR1 to ASBR4 following the path ASBR1-ASBR2-ASBR4 and
protecting against a failure of the ASBR1-ASBR4 link
o B2 from ASBR1 to R3 following the path
ASBR1-ASBR2-ASBR3-ASBR6-ASBR5-R3 and protecting against a failure of
the ASBR4 node.
o B3 from ASBR1 to ASBR7 following the path
ASBR1-ASBR2-ASBR3-ASBR6-ASBR7 and protecting against a failure of the
ASBR4 node.
o B4 from R3 to ASBR9 following the path R3-R4-ASBR8-ASBR10-ASBR9 and
protecting against a failure of the ASBR7 node.
o B5 from ASBR4 to ASBR9 following the path ASBR4-ASBR8-ASBR10-ASBR9
and protecting against a failure of the ASBR7 node.
6.2. Setup Operation
Let us consider an inter-AS TE LSP setup from R0 to R6, with example
paths p1, p2 each. In this example, we will examine the behavior on
node ASBR4 which is the boundary node for AS-2, for the different
signaling methods.
Contiguous:-
The head-end node, R0, that desires to setup an end-to-end contiguous
TE LSP, MAY originate a Path message with LSP_ATTRIBUTES object with
the "Contiguous LSP" bit set in the Attributes Flags TLV.
For path p1, additional computation to expand the loose hops may be
required at various hops along the LSP path. When the Path message
arrives at ASBR4, it may carry out a path computation or use some
other means to find the intermediate hops to reach ASBR7. It may then
Ayyangar and Vasseur [Page 11]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
adjust the outgoing ERO and forward the Path message through the
intermediate hops in AS-2 to ASBR7.
For path p2, the ERO next hop points to a node within the domain.
ASBR4 may then directly forward the Path message to the next hop in
the ERO.
Nesting and Stitching:-
When the Path message for the inter-AS TE LSP from R0 to R6, reaches
ASBR4, ASBR4 SHOULD first determine from the ERO hops, the boundary
node to the domain along the path. In this example, the domain
boundary node for all paths is ASBR7. It SHOULD then use the ERO hops
upto ASBR7 to find an existing FA-LSP in case of nesting or LSP
segment in case of stitching, that satisfies the TE constraints. If
there are no existing FA-LSPs or LSP segments and ASBR4 is capable of
seting up the FA-LSP or LSP segment on demand, it SHOULD do so using
the ERO hops in the Path message of the inter-domain TE LSP. In
either case, ASBR4 will adjust the ERO in the inter-domain TE LSP and
will forward the Path message directly to the end-point of the FA-LSP
or LSP segment using the procedures described in [LSP-HIERARCHY].
In case of path p1, since there are no ERO hops between ASBR4 and
ASBR7, and ASBR7 hop is loose, ASBR4 may select any existing FA-LSP
(nesting) or LSP segment (stitching) that satisfies the constraints
or it may compute a path for the FA-LSP or LSP segment upto ASBR7 or
some other intermediate node in AS-2.
In case of path p2, ASBR4 may either select an existing FA-LSP or LSP
segment with ERO hops link[ASBR4-R3](strict)-link[R3-ASBR7](strict)
or it may compute a new path for the FA-LSP or LSP segment using the
above hops. In either case, the ERO hops for the FA-LSP or LSP
segment MUST be the same as the signaled strict hops in that domain.
Now, suppose, we have a path p3, as a set of strict node hops
crossing AS-2 as defined below,
R0-X1-ASBR1(loose)-ASBR4(strict)-ASBR7(strict)-ASBR9(loose)-R6
In this case, the ERO nexthop at ASBR4 is ASBR7(strict). In this
case, ASBR4 will try to find or compute a FA-LSP or LSP segment
directly to ASBR7.
The main difference between processing of p1 and p3 for nesting or
stitching is that in case of p1, since the ERO nexthop is a loose
hop, ASBR4 need not find a FA-LSP or LSP segment directly from ASBR4
to ASBR7. So, there could be multiple FA-LSPs or LSP segments between
ASBR4 and ASBR7. On the other hand, for path p3, since ASBR7 is a
Ayyangar and Vasseur [Page 12]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
strict hop, ASBR4 MUST find or signal a FA-LSP or LSP segment that
connects ASBR4 and ASBR7.
7. Protection and recovery of inter-domain TE LSPs
7.1. Fast Recovery support using MPLS TE Fast Reroute
[FAST-REROUTE] describes two methods for local protection for a
packet TE LSP in case of link, SRLG or node failure. This section
describes how these mechanisms work with the proposed signaling
solutions for inter-domain TE LSP setup.
7.1.1. Failure within a domain (link or node failure)
The mode of operation of MPLS TE Fast Reroute to protect a
contiguous, stitched or nested TE LSP within a domain is identical to
the existing procedures described in [FAST-REROUTE]. In case of
nested or stitched inter-domain TE LSPs, protecting the intra-domain
TE FA-LSP or LSP segment will automatically protect the traffic on
the inter-domain TE LSP. No new extensions are required for any of
the signaling methods.
7.1.2. Failure of link at domain boundaries
The procedures for doing link protection of the link at domain
boundaries is the same for contiguous, nested and stitched TE LSPs.
To protect an inter-domain link with MPLS TE Fast Reroute, a set of
backup tunnels must be configured or dynamically computed between the
two domain boundary nodes diversely routed from the protected inter-
domain link. The region connecting two domains may not be TE enabled.
In this case, an implementation will have to support the set up of TE
LSP over a non-TE enabled region.
For each protected inter-domain TE LSP traversing the protected link,
a NHOP backup must be selected by a PLR (i.e domain exit boundary
router), when the TE LSP is first set up. This requires for the PLR
to select a bypass tunnel terminating at the NHOP. Finding the NHOP
bypass tunnel of an inter-AS LSP can be achieved by analyzing the
content of the RRO object received in the RSVP Resv message of both
the bypass tunnel and the protected TE LSP(s). As defined in [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). The PLR may or
may not have sufficient topology information to find where the backup
tunnel intersects the protected TE LSP based on the RRO. [NODE-ID]
proposes a solution to this issue, defining an additional RRO IPv4
Ayyangar and Vasseur [Page 13]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
suboject that specifies a node-id address.
Example: The ASBR1-ASBR4 link is protected by the backup tunnel B1
that follows the ASBR1-ASBR2-ASBR4 path
7.1.3. Failure of a boundary node
For each protected inter-domain TE LSP traversing the boundary node
to be protected, a NNHOP backup must be selected by the PLR. This
requires the PLR to setup a bypass tunnel terminating at the NNHOP.
Finding the NNHOP bypass tunnel of an inter-domain TE LSP can be
achieved by analyzing the content of the RRO object received in the
RSVP Resv message of both the bypass tunnel and the protected TE
LSP(s) (see [NODE-ID]). The main difference with node protection,
between a protected contiguous inter-domain TE LSP and a protected
nested or stitched inter-domain TE LSP is that the PLR and NNHOP (MP)
in case of a contiguous TE-LSP could be any node within the domain.
However, in case of a nested or stitched TE-LSP the PLR and MP can
only be the end-points of the FA-LSP or LSP segment. The consequence
is that the backup path is likely to be longer and if bandwidth
protection is desired, for instance, ([FAST-REROUTE]) more resources
may be reserved in the domain than necessary.
Let us again consider the example topology of section 4.1. The
protected inter-domain TE LSP is an inter-AS TE LSP from R0 to R6
with path p1. Also, for nesting or stitching, let us assume that the
end-points of the FA-LSP or LSP segment in AS-2 are ASBR4 and ASBR7.
This gives rise to the following two scenarios for node protection:
Protecting the boundary node at the entry to a domain :-
Example: protecting against the failure of ASBR4
If the inter-AS TE LSP in this example, is a contiguous LSP, then the
PLR is ASBR1 and the NNHOP (MP) could be R3 or any other intermediate
node along the LSP path. A backup tunnel B2 may be used to protect
the inter-AS TE LSP against failure of ASBR4.
If the inter-AS TE LSP in this example, is nested or sticthed at
ASBR4 into an intra-domain TE FA-LSP or LSP segment between ASBR4 and
ASBR7, then the PLR is ASBR1 and the NNHOP (MP) is ASBR7. A backup
tunnel B3 may be used to protect the inter-AS TE LSP against failure
of ASBR4.
Protecting the boundary node at the exit of a domain :-
Example: protecting against failure of ASBR7.
Ayyangar and Vasseur [Page 14]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
If the inter-AS TE LSP in this example, is a contiguous LSP, then the
PLR could be R3 and the NNHOP (MP) is ASBR9. A backup tunnel B4 may
be used to protect the inter-AS TE LSP against failure of ASBR7.
If the inter-AS TE LSP in this example, is nested or sticthed at
ASBR4 into an intra-domain TE FA-LSP or LSP segment between ASBR4 and
ASBR7, then the PLR is ASBR4 and the NNHOP (MP) is ASBR9. A backup
tunnel B5 may be used to protect the inter-AS TE LSP against failure
of ASBR7.
7.2. Protection and recovery of GMPLS LSPs
[E2E-RECOVERY] describes the signaling extensions to support end-to-
end GMPLS LSP recovery. Signaling methods defined above for inter-
domain RSVP-TE LSPs also apply to recovery LSPs signaled for end-to-
end protection of inter-domain GMPLS LSPs. Any other protection
mechanisms that are developed for GMPLS LSPs SHOULD also take into
account inter-domain considerations.
8. Re-optimization of inter-domain TE LSPs
Re-optimization of a TE LSP is the process of moving the LSP from the
current path to a more prefered path. This usually involves
computation of the new prefered path and make-before-break signaling
procedures [RSVP-TE], to minimize traffic disruption. The path
computation procedures involved in re-optimization of an inter-domain
TE LSP are covered in [INTER-DOMAIN-PATH-COMP].
In the context of an inter-domain TE LSP, since the LSP traverses
multiple domains, re-optimization may be required in one or more
domains at a time. Again, depending on the nature of the LSP and/or
policies and configuration at domain boundaries (or other nodes), one
may either always want the head-end node of the inter-domain TE LSP
to be notified of any local need for re-optimizations and let the
head-end initiate the make-before-break process or one may want to
restrict local re-optimizations with the domain.
[LOOSE-REOPT] describes mechanisms that allow,
- The head-end node to trigger on every node whose next hop
is a loose hop the re-evaluation of the current path in order to
detect a potentially more optimal path. This is done via explicit
signaling request: the head-end node sets the "ERO Expansion request"
bit of the SESSION-ATTRIBUTE object carried in the RSVP Path message.
- A node whose next hop is a loose-hop to signal to the head-
end node that a better path exists. This is performed by sending an
RSVP Path Error Notify message (ERROR-CODE = 25), sub-code 6 (Better
path exists). This indication may either be sent in response to a
Ayyangar and Vasseur [Page 15]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
query sent by the head-end node or spontaneously by any node having
detected a more optimal path.
The above mechanisms SHOULD be used for a contiguous inter-domain TE
LSP to allow the head-end node of the inter-domain TE LSP to initiate
make-before-break procedures. For nested or stitched TE LSPs, it is
possible to re-optimize the local FA-LSP or LSP segment without
involving the head-end node of the inter-domain TE LSP. This will
automatically re-route the traffic for the inter-domain TE LSP along
the new path, within the domain. Such local re-optimizations,
including parameters for re-optimization can be controlled by local
policy or configuration in that domain.
9. Security Considerations
When signaling an inter-domain RSVP-TE LSP, an operator may make use
of the already defined security features related to RSVP-TE
(authentication). This may require some coordination between the
domains to share the keys (see RFC 2747 and RFC 3097).
10. IANA Considerations
The following values have to be defined by IANA for this document.
The registry is, http://www.iana.org/assignments/rsvp-parameters.
10.1. Attribute Flags for LSP_ATTRIBUTES object
The following two new flag bits are being defined for the Attributes
Flags TLV in the LSP_ATTRIBUTES object. The numeric values should be
assigned by IANA.
Contiguous LSP bit - 0x01 (Suggested value)
LSP stitching desired bit - 0x02 (Suggested value)
Both these flag bits are only to be used in the Attributes Flags TLV
on a Path message.
The 'LSP stitching desired bit' has a corresponding 'LSP segment
stitching ready' bit to be used in the RRO Attributes sub-object.
Ayyangar and Vasseur [Page 16]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
10.2. New Error Codes
The following two new error sub-codes are being defined under the
RSVP error-code "Routing Problem" (24). The numeric error sub-code
values should be assigned by IANA.
Contiguous LSP type not supported - sub-code 17 (Suggested value)
Stitching unsupported - sub-code 16 (Suggested value)
These error codes are to be used only in a RSVP PathErr.
11. Acknowledgements
The authors would like to acknowledge the input and helpful comments
from Adrian Farrel on various aspects discussed in the document.
12. References
12.1. Normative References
[OSPF-TE] Katz, D., Yeung, D., Kompella, K., "Traffic Engineering
Extensions to OSPF", RFC 3630 (Updates RFC 2370), September 2003.
[ISIS-TE] Smit, H., Li, T., "IS-IS extensions for Traffic
Engineering", RFC 3784
[RSVP-TE] Awduche, et al, "Extensions to RSVP for LSP Tunnels", RFC
3209, December 2001.
[RSVP-GMPLS] L. Berger, et al, "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Extensions", RFC 3473, January 2003.
[LSP-HIERARCHY] Kompella K., Rekhter Y., "LSP Hierarchy with
Generalized MPLS TE", (work in progress).
[CRANKBACK] Farrel A. et al, "Crankback Signaling Extensions for MPLS
Signaling", (work in progress).
[LSP-ATTRIBUTES] Farrel A. et al, "Encoding of Attributes for
Multiprotocol Label Switching (MPLS) Label Switched Path (LSP)
Establishment Using RSVP-TE", (work in progress).
[FAST-REROUTE] Ping Pan, et al, "Fast Reroute Extensions to RSVP-TE
for LSP Tunnels", (work in progress)
Ayyangar and Vasseur [Page 17]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
[NODE-ID] Vasseur, Ali and Sivabalan, "Definition of an RRO node-id
subobject", (work in progress).
[E2E-RECOVERY] J.P. Lang et al, "RSVP-TE Extensions in support of
End-to-End GMPLS-based Recovery", (work in progress).
12.2. Informative References
[INTER-AS-TE-REQS] Zhang et al, "MPLS Inter-AS Traffic Engineering
requirements", (work in progress).
[INTER-AREA-TE-REQS] LeRoux JL, Vasseur JP, Boyle J. et al,
"Requirements for support of Inter-Area MPLS Traffic Engineering",
(work in progress).
[INTER-DOMAIN-FRAMEWORK] Farrel A. et al, "A Framework for Inter-
Domain MPLS Traffic Engineering", (work in progress).
[INTER-DOMAIN-PATH-COMP] Vasseur JP., Ayyangar A., Zhang R., "Inter-
domain MPLS Traffic Engineering LSP path computation methods", (work
in progress).
[GMPLS-OVERLAY] G. Swallow et al, "GMPLS RSVP Support for the Overlay
Model", (work in progress).
[RSVP-UNNUM] Kompella K., Rekhter Y., "Signalling Unnumbered Links in
Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)", RFC
3477, January 2003.
[BUNDLING] Kompella K., Rekhter Y., "Link Bundling in MPLS Traffic
Engineering", (work in progress).
[LOOSE-REOPT] Vasseur JP. et al, "Reoptimization of an explicit
loosely routed MPLS TE paths", (work in progress).
Author's addresses
Ayyangar and Vasseur [Page 18]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
Arthi Ayyangar
Juniper Networks, Inc.
1194 N.Mathilda Ave
Sunnyvale, CA 94089
USA
e-mail: arthi@juniper.net
Jean Philippe Vasseur
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough , MA - 01719
USA
e-mail: jpv@cisco.com
Intellectual Property Statement
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.
Ayyangar and Vasseur [Page 19]
draft-ayyangar-ccamp-inter-domain-rsvp-te-01.txt October 2004
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2004). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Ayyangar and Vasseur [Page 20]