draft-ietf-ccamp-inter-domain-pd-path-comp-00.txt   draft-ietf-ccamp-inter-domain-pd-path-comp-01.txt 
CCAMP Working Group JP Vasseur (Editor) Network Working Group JP Vasseur (Editor)
IETF Internet draft Cisco Systems, Inc. IETF Internet draft Cisco Systems, Inc.
Proposed Status: Standard Arthi Ayyangar (Editor) Proposed Status: Standard Arthi Ayyangar (Editor)
Juniper Networks Juniper Networks
Raymond Zhang Raymond Zhang
Infonet Service Corporation Infonet Service Corporation
Expires: October 2005 Expires: April 2006
April 2005 October 2005
draft-ietf-ccamp-inter-domain-pd-path-comp-00.txt draft-ietf-ccamp-inter-domain-pd-path-comp-01.txt
A Per-domain path computation method for computing Inter-domain Traffic A Per-domain path computation method for establishing Inter-domain
Engineering (TE) Label Switched Path (LSP) Traffic Engineering (TE) Label Switched Paths (LSPs)
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Abstract Abstract
This document specifies a per-domain path computation method for This document specifies a per-domain path computation technique for
computing inter-domain Traffic Engineering (TE) Multiprotocol Label establishing inter-domain Traffic Engineering (TE) Multiprotocol Label
Switching (MPLS) and Generalized MPLS (GMPLS) Label Switched (LSP) Switching (MPLS) and Generalized MPLS (GMPLS) Label Switched Paths
paths. In this document a domain is referred to as a collection of (LSPs). In this document a domain refers to a collection of network
network elements within a common sphere of address management or path elements within a common sphere of address management or path
computational responsibility such as IGP areas and Autonomous Systems. computational responsibility such as IGP areas and Autonomous Systems.
Per-domain computation applies where the full path of an inter-domain
TE LSP cannot be or is not determined at the ingress node of the TE
Vasseur, Ayyangar and Zhang 1 Vasseur, Ayyangar and Zhang 1
The principle of per-domain path computation specified in this document LSP, and is not signaled across domain boundaries. This is most likely
comprises of a GMPLS or MPLS node along an inter-domain LSP path, to arise owing to TE visibility limitations. The signaling message
computing a path up to the last reachable hop within its domain. It indicates the destination and nodes up to the next domain boundary. It
covers cases where this last hop (domain exit point) may already be may also indicate further domain boundaries or domain identifiers. The
specified in the signaling message as well the case where this last hop path through each domain, possibly including the choice of exit point
may need to be determined by the GMPLS node. from the domain, must be determined within the domain.
Conventions used in this document Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
Table of content Table of content
1. Terminology ............................................. 3 1. Terminology..................................................3
2. Introduction ............................................ 4 2. Introduction.................................................3
3. General assumptions ..................................... 5 3. General assumptions..........................................4
4. Per-Domain path computation algorithm ................... 8 3.1 Common assumptions..........................................4
4.1 Example with an inter-area TE LSP ...................... 9 3.2 Example of topology for the inter-area TE case .............5
4.1.1 Case 1: T1 is a contiguous TE LSP .................... 9 3.3 Example of topology for the inter-AS TE case ...............6
4.1.2 Case 2: T1 is a stitched or nested TE LSP ............ 10 4. Per-domain path computation procedures.......................7
4.2 Example with an inter-AS TE LSP ........................ 11 4.1 Example with an inter-area TE LSP...........................10
4.2.1 Case 1: T1 is a contiguous TE LSP ................... 12 4.1.1 Case 1: T1 is a contiguous TE LSP.........................10
4.2.2 Case 2: T1 is a stitched or nested TE LSP ........... 13 4.1.2 Case 2: T1 is a stitched or nested TE LSP.................11
5 Path optimality/diversity ................................ 13 4.2 Example with an inter-AS TE LSP.............................11
6 MPLS Traffic Engineering Fast Reroute for inter-domain 4.2.1 Case 1: T1 is a contiguous TE LSP.........................12
TE LSPs ................................................. 13 4.2.2 Case 2: T1 is a stitched or a nested TE LSP...............12
6.1 Failure of an internal network element ................. 14 5. Path optimality/diversity....................................13
6.2 Failure of an inter-ASBR links (inter-AS TE) ........... 14 6. Reoptimization of an inter-domain TE LSP.....................13
6.3 Failure of an ABR or an ASBR node ...................... 14 6.1 Contiguous TE LSPs..........................................13
7. Reoptimization of an inter-domain TE LSP ................ 14 6.2. Stitched or nested (non-contiguous) TE LSPs................13
7.1 Contiguous TE LSPs ..................................... 14 6.3 Path characteristics after reoptimization...................15
7.2 Stitched or nested (non-contiguous) TE LSPs ............ 15 7. Security Considerations .....................................15
8. Security Considerations ................................. 16 8. Intellectual Property Considerations ........................15
9. Intellectual Property Considerations .................... 17 9. Acknowledgments..............................................15
10 References .............................................. 17 10. References..................................................15
10.1 Normative references .................................. 17 10.1 Normatives References .....................................16
10.2 Informative references ................................ 18 10.2 Informative References ....................................17
Vasseur, Ayyangar and Zhang 2 Vasseur, Ayyangar and Zhang 2
1. Terminology 1. Terminology
ABR Routers: routers used to connect two IGP areas (areas in OSPF or ABR Routers: routers used to connect two IGP areas (areas in OSPF or
L1/L2 in IS-IS) levels in IS-IS)
Boundary LSR: a boundary LSR is either an ABR in the context of inter-
area MPLS TE or an ASBR in the context of inter-AS MPLS TE.
Bypass Tunnel: an LSP that is used to protect a set of LSPs passing
over a common facility.
CSPF: Constraint-based Shortest Path First.
Fast Reroutable LSP: any LSP for which the "Local protection desired"
bit is set in the Flag field of the SESSION_ATTRIBUTE object of its
Path messages or signaled with a FAST-REROUTE object.
Interconnect routers or ASBR routers: routers used to connect together
ASes of a different or the same Service Provider via one or more Inter-
AS links.
Inter-AS MPLS TE LSP: A TE LSP whose head-end LSR and tail-end LSR do
not reside within the same Autonomous System (AS), or whose head-end
LSR and tail-end LSR are both in the same AS but the TE LSPĂs path
may be across different ASes. Note that this definition also applies to
TE LSP whose Head-end and Tail-end LSRs reside in different sub-ASes
(BGP confederations).
Inter-area MPLS TE LSP: A TE LSP where the head-end LSR and tail-end
LSR do not reside in the same area or both the head-end and tail end
LSR reside in the same area but the TE LSP transits one or more
different areas along the path.
LSR: Label Switch Router
LSP: MPLS Label Switched Path
Local Repair: local protection techniques used to repair TE LSPs
quickly when a node or link along the LSPs path fails.
MP: Merge Point. The LSR where bypass tunnels meet the protected LSP. ASBR Routers: routers used to connect together ASes of a different or
the same Service Provider via one or more Inter-AS links.
NHOP Bypass Tunnel: Next-Hop Bypass Tunnel. A backup tunnel which Boundary LSR: a boundary LSR is either an ABR in the context of inter-
bypasses a single link of the protected LSP. area TE or an ASBR in the context of inter-AS TE.
NNHOP Bypass Tunnel: Next-Next-Hop Bypass Tunnel. A backup tunnel which Inter-AS TE LSP: A TE LSP that crosses an AS boundary.
bypasses a single node of the protected LSP.
Vasseur, Ayyangar and Zhang 3 Inter-area TE LSP: A TE LSP that crosses an IGP area.
PCE: Path Computation Element. An LSR in charge of computing TE LSP LSR: Label Switching Router
path for which it is not the Head-end. For instance, an ABR (inter-
area) or an ASBR (Inter-AS) can play the role of PCE.
PCC: Path Computation Client (any head-end LSR) requesting a path LSP: Label Switched Path
computation from the Path Computation Element.
Protected LSP: an LSP is said to be protected at a given hop if it has TE LSP: Traffic Engineering Label Switched Path
one or multiple associated backup tunnels originating at that hop.
PLR: Point of Local Repair. The head-end of a bypass tunnel. 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.
TED: MPLS Traffic Engineering Database TED: Traffic Engineering Database
The notion of contiguous, stitched and nested TE LSPs is defined in The notion of contiguous, stitched and nested TE LSPs is defined in
[INTER-DOMAIN-SIG] and [LSP-STITCHING] and will not be repeated here. [INT-DOMAIN-FRWK] and will not be repeated here.
2. Introduction 2. Introduction
The requirements for inter-area and inter-AS MPLS Traffic Engineering The requirements for inter-domain Traffic Engineering (inter-area and
have been developed by the Traffic Engineering Working Group and have inter-AS TE) have been developed by the Traffic Engineering Working
been stated in [INTER-AREA-REQS] and [INTER-AS-REQS] respectively. The Group and have been stated in [INT-AREA-REQS] and [INT-AS-REQS]. The
framework for inter-domain MPLS Traffic Engineering has been provided framework for inter-domain MPLS Traffic Engineering has been provided
in [INTER-DOMAIN-FRAMEWORK]. in [INT-DOMAIN-FRWK].
The set of mechanisms to establish and maintain inter-domain TE LSPs Some of the mechanisms used to establish and maintain inter-domain TE
are specified in [INTER-DOMAIN-SIG] and [LSP-STITCHING]. LSPs are specified in [INTER-DOMAIN-SIG] and [LSP-STITCHING].
This document exclusively focuses on the path computation aspects and This document exclusively focuses on the path computation aspects and
defines a method for computing inter-domain TE LSP paths where each defines a method for establishing inter-domain TE LSP where each node
node in charge of computing a section of an inter-domain TE LSP path is in charge of computing a section of an inter-domain TE LSP path is
always along the path of such LSP. always along the path of such TE LSP.
When the visibility of an end to end complete path spanning multiple When the visibility of an end to end complete path spanning multiple
domains is not available at the head end node, one approach described domains is not available at the Head-end LSR, one approach described in
in the document consists of using a per-domain path computation scheme this document consists of using a per-domain path computation technique
used during LSP setup to determine the inter-domain LSP path as it
traverses multiple domains.
Note that the mechanisms proposed in this document could also be Vasseur, Ayyangar and Zhang 3
applicable to MPLS TE domains other than areas and ASes.
According to the wide set of requirements defined in [INTER-AS-TE-REQS] during LSP setup to determine the inter-domain TE LSP as it traverses
and [INTER-AREA-TE-REQS], coming up with a single solution covering all multiple domains.
the requirements is certainly possible but may not be desired: indeed,
as described in [INTER-AS-TE-REQS] the spectrum of deployment scenarios
is quite large and designing a solution addressing the super-set of all
the requirements would lead to providing a rich set of mechanisms not
required in several cases. Depending on the deployment scenarios of a
SP, certain requirements stated above may be strict while certain other
requirements may be relaxed.
Vasseur, Ayyangar and Zhang 4 The mechanisms proposed in this document are also applicable to MPLS TE
domains other than IGP areas and ASes.
There are different ways in which inter-domain TE LSP path computation The solution described in this document does not attempt to address all
may be performed. For example, if the requirement is to get an end-to- the requirements specified in [INT-AREA-REQS] and [INT-AS-REQS]. This
end constraint-based shortest path across multiple domains, then a is acceptable according to [INT-AS-REQS] which indicates that a
mechanism using one or more distributed PCEs could be used to compute solution may be developed to address a particular deployment scenario
the shortest path across different domains. Alternatively, one could and might, therefore, not meet all requirements for other deployment
also use some static or discovery mechanisms to determine the next scenarios.
boundary LSR per domain as the inter-domain TE LSP is being signaled.
Other offline mechanisms for path computation are not precluded either.
Depending on the Service ProviderĂs requirements, one may adopt either
of these techniques for inter-domain path computation.
Note that the adequate path computation method may be chosen based upon It must be pointed out that the inter-domain path computation technique
the TE LSP characteristics and requirements. This document specifies an proposed in this document is one among many others and the choice of
inter-domain path computation technique based on per-domain path the appropriate technique must be driven by the set of requirements for
computation and could be used in place or in conjunction with other the paths attributes and the applicability to a particular technique
techniques. with respect to the deployment scenario. For example, if the
requirement is to get an end-to-end constraint-based shortest path
across multiple domains, then a mechanism using one or more distributed
PCEs could be used to compute the shortest path across different
domains (see [PCE-ARCH]). Other offline mechanisms for path computation
are not precluded either. Note also that a Service Provider may elect
to use different inter-domain path computation techniques for different
TE LSP types.
3. General assumptions 3. General assumptions
In the rest of this document, we make the following set of assumptions: In the rest of this document, we make the following set of assumptions:
1) Common assumptions 3.1. Common assumptions
- Each domain in all the examples below is assumed to be capable of - Each domain in all the examples below is assumed to be capable of
doing Traffic Engineering (i.e. running OSPF-TE or ISIS-TE and RSVP- doing Traffic Engineering (i.e. running OSPF-TE or ISIS-TE and RSVP-
TE). A domain may itself comprise multiple other domains. E.g. An AS TE). A domain may itself comprise multiple other domains. E.g. An AS
may itself be composed of several other sub-AS(es) (BGP confederations) may itself be composed of several other sub-AS(es) (BGP confederations)
or areas/levels. or areas/levels. In this case, the path computation technique described
for inter-area and inter-AS MPLS Traffic Engineering just recursively
- The inter-domain LSPs are signaled using RSVP-TE ([RSVP-TE]). applies.
- The path (ERO) for the inter-domain TE LSP traversing multiple
areas/ASes may be signaled as a set of (loose and/or strict) hops. The
hops may identify:
- The complete strict path end to end across different
areas/ASes
- The complete strict path in the source area/AS followed by
boundary LSRs (and domain identifiers, e.g. AS numbers)
- The complete list of boundary LSRs along the path
- The current boundary LSR and the LSP destination
In this case, the set of (loose or strict) hops can either be - The inter-domain TE LSPs are signaled using RSVP-TE ([RSVP-TE]).
statically configured on the Head-end LSR or dynamically computed. In
the former case, the resulting path is statically configured on the
Head-end LSR. In the latter case (dynamic computation), a per-domain
path computation method is defined in this document with some Auto-
discovery mechanism based on BGP and/or IGP information yielding the
next-hop boundary node (domain exit point, say ABR/ASBR) along the path
as the LSP is being signaled, along with crankback mechanisms. Note
Vasseur, Ayyangar and Zhang 5 - The path (ERO) for an inter-domain TE LSP may be signaled as a set of
(loose and/or strict) hops. The hops may identify:
* The complete strict path end-to-end across different domains
* The complete strict path in the source domain followed by
boundary LSRs (or domain identifiers, e.g. AS numbers)
* The complete list of boundary LSRs along the path
* The current boundary LSR and the LSP destination
that alternatively next-hop may be statically configured on the Head- Vasseur, Ayyangar and Zhang 4
end LSR in which case next-hop auto-discovery would not be needed.
- Furthermore, the boundary LSRs are assumed to be capable of The set of (loose or strict) hops can either be statically configured
performing local path computation for expansion of a loose next-hop in on the Head-end LSR or dynamically computed. A per-domain path
the signaled ERO if the path is not signaled by the head-end LSR as a computation method is defined in this document with an optional Auto-
set of strict hops or if the strict hop is an abstract node (e.g. an discovery mechanism based on IGP and/or BGP information yielding the
AS). This can be done by performing a CSPF computation up to that next next-hop boundary node (domain exit point, such as ABR/ASBR) along the
loose hop as opposed to the TE LSP destination or by making use of some path as the TE LSP is being signaled, along with potential crankback
PCEs. In any case, no topology or resource information needs to be mechanisms. Alternatively the domain exit points may be statically
distributed between areas/ASes (as mandated per [INTER-AREA-REQS] and configured on the Head-end LSR in which case next-hop boundary node
[INTER-AS-REQS]), which is critical to preserve IGP/BGP scalability and auto-discovery would not be required.
confidentiality in the case of TE LSPs spanning multiple routing
domains.
Note that PCE-based path computation may be mentioned in this document - Boundary LSRs are assumed to be capable of performing local path
for the sake of reference but such techniques are outside the scope of computation for expansion of a loose next-hop in the signaled ERO if
this document. the path is not signaled by the Head-end LSR as a set of strict hops or
if the strict hop is an abstract node (e.g. an AS). In any case, no
topology or resource information needs to be distributed between
domains (as mandated per [INT-AREA-REQS] and [INT-AS-REQS]), which is
critical to preserve IGP/BGP scalability and confidentiality in the
case of TE LSPs spanning multiple routing domains.
- The paths for the intra-domain FA-LSPs or LSP segments or for a - The paths for the intra-domain Hierarchical LSPs (H-LSP) or S-LSPs
contiguous TE LSP within the area/AS, may be pre-configured or computed (S-LSP) or for a contiguous TE LSP within the domain may be pre-
dynamically based on the arriving inter-domain LSP setup request; configured or computed dynamically based on the arriving inter-domain
depending on the requirements of the transit area/AS. Note that this LSP setup request (depending on the requirements of the transit
capability is explicitly specified as a requirement in [INTER-AS-TE- domain). Note that this capability is explicitly specified as a
REQS]. When the paths for the FA-LSPs/LSP segments are pre-configured, requirement in [INT-AS-REQS]. When the paths for the H-LSPs/S-LSP are
the constraints as well as other parameters like local protection pre-configured, the constraints as well as other parameters like local
scheme for the intra-area/AS FA-LSP/LSP segment are also pre- protection scheme for the intra-domain H-LSP/S-LSP are also pre-
configured. configured.
- While certain constraints like bandwidth can be used across different - While certain constraints like bandwidth can be used across different
areas/ASes, certain other TE constraints like resource affinity, color, domains, certain other TE constraints like resource affinity, color,
metric, etc. as listed in [RFC2702] could be translated at areas/ASes metric, etc. as listed in [RFC2702] may need to be translated at domain
boundaries. If required, it is assumed that, at the area/AS boundary boundaries. If required, it is assumed that, at the domain boundary
LSRs, there will exist some sort of local mapping based on offline LSRs, there will exist some sort of local mapping based on policy
policy agreement, in order to translate such constraints across area/AS agreement in order to translate such constraints across domain
boundaries. It is expected that such an assumption particularly applies boundaries. It is expected that such an assumption particularly applies
to inter-AS TE: for example, the local mapping would be similar to the to inter-AS TE: for example, the local mapping would be similar to the
Inter-AS TE Agreement Enforcement Polices stated in [INTER-AS-TE-REQS]. Inter-AS TE Agreement Enforcement Polices stated in [INT-AS-REQS].
2) Example of topology for the inter-area TE case 3.2. Example of topology for the inter-area TE case
The following example will be used for the inter-area TE case in this The following example will be used for the inter-area TE case in this
document. document.
<--area1--><---area0---><----area2-----> <-area 1-><-- area 0 --><--- area 2 --->
------ABR1------------ABRĂ1------- ------ABR1------------ABR3-------
| / | | \ | | / | | \ |
R0--X1 | | X2---X3--R1 R0--X1 | | X2---X3--R1
| | | / | | | | / |
-------ABR2-----------ABRĂ2------ ------ABR2-----------ABR4--------
<=========== Inter-area TE LSP =======> <=========== Inter-area TE LSP =======>
Vasseur, Ayyangar and Zhang 6 Vasseur, Ayyangar and Zhang 5
Figure 1 - Example of topology for the inter-area TE case
Assumptions Description of Figure 1:
- ABR1, ABR2, ABRĂ1 and ABRĂ2 are ABRs, - ABR1, ABR2, ABR3 and ABR4 are ABRs,
- X1: an LSR in area 1, - X1: an LSR in area 1,
- X2, X3: LSRs in area 2, - X2, X3: LSRs in area 2,
- An inter-area TE LSP T0 originated at R0 in area1 and terminating at - An inter-area TE LSP T0 originated at R0 in area1 and terminating at
R1 in area2, R1 in area 2.
Notes: Notes:
- The terminology used in the example above corresponds to OSPF but the - The terminology used in the example above corresponds to OSPF but the
path computation methods proposed in this document equally applies to path computation technique proposed in this document equally applies to
the case of an IS-IS multi-levels network. the case of an IS-IS multi-level network.
- Just a few routers in each area are depicted in the diagram above for - Just a few routers in each area are depicted in the diagram above for
the sake of simplicity. the sake of simplicity.
- The example depicted in Figure 1 shows the case where the Head-end
and Tail-end areas are connected by means of area 0. The case of an
inter-area TE LSP between two IGP areas that does not transit through
area 0 is not precluded.
3) Example of topology for the inter-AS TE case: 3.3. Example of topology for the inter-AS TE case
We will consider the following general case, built on a superset of the We consider the following general case, built on a superset of the
various scenarios defined in [INTER-AS-TE-REQS]: various scenarios defined in [INT-AS-REQS]:
<-- AS 1 ---> <------- AS 2 -----><--- AS 3 ----> <-- AS 1 ---> <------- AS 2 -----><--- AS 3 ---->
<---BGP---> <---BGP--> <---BGP---> <---BGP-->
CE1---R0---X1-ASBR1-----ASBR4¨-R3---ASBR7-¨--ASBR9----R6 CE1---R0---X1-ASBR1-----ASBR4--R3---ASBR7----ASBR9----R6
|\ \ | / | / | / | | | |\ \ | / | / | / | | |
| \ ASBR2---/ ASBR5 | -- | | | | \ ASBR2---/ ASBR5 | -- | | |
| \ | | |/ | | | | \ | | |/ | | |
R1-R2¨--ASBR3¨----ASBR6¨-R4---ASBR8¨---ASBR10¨--R7---CE2 R1-R2---ASBR3----ASBR6--R4---ASBR8----ASBR10---R7---CE2
<======= Inter-AS TE LSP(LSR to LSR)===========> <======= Inter-AS TE LSP(LSR to LSR)===========>
or or
<======== Inter-AS TE LSP (CE to ASBR => <======== Inter-AS TE LSP (CE to ASBR =>
or or
<================= Inter-AS TE LSP (CE to CE)===============> Formatted: <================= Inter-AS TE LSP (CE to CE)===============>
The diagram above covers all the inter-AS TE deployment cases described Figure 2 - Example of topology for the inter-AS TE case
in [INTER-AS-TE-REQS].
Assumptions: The diagram depicted in Figure 2 covers all the inter-AS TE deployment
cases described in [INT-AS-REQS].
- Three interconnected ASes, respectively AS1, AS2, and AS3. Note that Description of Figure 2:
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 Vasseur, Ayyangar and Zhang 6
single hop links interconnecting the ASBRs and also referred to as
inter-ASBR links,
Vasseur, Ayyangar and Zhang 7 - Three interconnected ASes, respectively AS1, AS2, and AS3. Note that
in some scenarios described in [INT-AS-REQS] AS1=AS3.
- The ASBRs in different ASes are BGP peers. There is usually no IGP
running on the single hop links interconnecting the ASBRs and also
referred to as inter-ASBR links.
- Each AS runs an IGP (IS-IS or OSPF) with the required IGP TE - Each AS runs an IGP (IS-IS or OSPF) with the required IGP TE
extensions (see [OSPF-TE] and [IS-IS-TE]). In other words, the ASes are extensions (see [OSPF-TE], [ISIS-TE], [G-OSPF] and [G-ISIS]). In other
TE enabled, words, the ASes are TE enabled,
- Each AS can be made of several IGP areas. The path computation - Each AS can be made of several IGP areas. The path computation
techniques described in this document applies to the case of a single technique described in this document applies to the case of a single AS
AS made of multiple IGP areas, multiples ASes made of a single IGP made of multiple IGP areas, multiples ASes made of a single IGP areas
areas or any combination of the above. For the sake of simplicity, each or any combination of the above. For the sake of simplicity, each
routing domain will be considered as single area in this document. routing domain will be considered as single area in this document. The
case of an Inter-AS TE LSP spanning multiple ASes where some of those
ASes are themselves made of multiple IGP areas can be easily derived
from the examples above: the per-domain path computation technique
described in this document is applied recursively in this case.
- An inter-AS TE LSP T1 originated at R0 in AS1 and terminating at R6 - An inter-AS TE LSP T1 originated at R0 in AS1 and terminating at R6
in AS3. in AS3.
4. Per-domain path computation algorithm 4. Per-domain path computation procedures
Regardless of the nature of the inter-domain TE LSP (contiguous, The mechanisms for inter-domain TE LSP computation as described in this
stitched or nested), a similar set of mechanisms for local TE LSP path document can be used regardless of the nature of the inter-domain TE
computation (next hop resolution) can be used. LSP (contiguous, stitched or nested).
When an ABR/ASBR receives a Path message with a loose next-hop or an Note that any path can be defined as a set of loose and strict hops. In
abstract node in the ERO, then it carries out the following actions: other words, in some cases, it might be desirable to rely on the
dynamic path computation in some area, and exert a strict control on
the path in other areas (defining strict hops).
1) It checks if the loose next-hop is accessible via the TED. If the When a boundary LSR (e.g. ABR/ASBR) receives a Path message with an ERO
loose next-hop is not present in the TED, then it checks if the next- that contains a loose hop or an abstract node that is not a simple
hop at least has IP reachability (via IGP or BGP). If the next-hop is abstract node (that is, an abstract node that identifies more than one
not reachable, then the path computation stops and the LSR sends back a LSR), then it MUST follow the procedures as described in [INTER-DOMAIN-
PathErr upstream. If the next-hop is reachable, then it finds an SIG]. In addition, the following procedures describe the path
ABR/ASBR to get to the next-hop. In the absence of an auto-discovery computation procedures that SHOULD be carried out on the LSR:
mechanism, the ABR in the case of inter-area TE or the ASBR in the
next-hop AS in the case of inter-AS TE should be the loose next-hop in 1) If the next hop boundary LSR is not present in the TED.
the ERO and hence should be accessible via the TED, otherwise the path
computation for the inter-domain TE LSP will fail. If the loose next-hop is not present in the TED, the following
conditions MUST be checked:
- If the IP address of the next hop boundary LSR is outside of the
current domain,
- If the domain is PSC (Packet Switch Capable) and uses in-band
control channel
Vasseur, Ayyangar and Zhang 7
If the two conditions above are satisfied then the boundary LSR SHOULD
check if the next-hop has IP reachability (via IGP or BGP). If the
next-hop is not reachable, then a signaling failure occurs and the LSR
SHOULD send back a PathErr message upstream with error code=24
("Routing Problem") and error subcode as described in section 4.3.4 of
[RSVP-TE]. If the next-hop is reachable, then it SHOULD find a domain
boundary LSR (domain boundary point) to get to the next-hop. The
determination of domain boundary point based on routing information is
what we term as "auto-discovery" in this document. In the absence of
such an auto-discovery mechanism, a) the ABR in the case of inter-area
TE or the ASBR in the next-hop AS in the case of inter-AS TE should be
the signaled loose next-hop in the ERO and hence should be accessible
via the TED or b) there needs to be an alternate scheme that provides
the domain exit points. Otherwise the path computation for the inter-
domain TE LSP will fail.
An implementation MAY support the ability to disable such IP
reachability fall-back option should the next hop boundary LSR not be
present in the TED. In other words, an implementation MAY support the
possibility to trigger a signaling failure whenever the next-hop is not
present in the TED.
2) If the next-hop boundary LSR is present in the TED. 2) If the next-hop boundary LSR is present in the TED.
a) Case of a contiguous TE LSP. The ABR/ASBR just performs an a) Case of a contiguous TE LSP. The boundary LSR that processes
ERO expansion (unless not allowed by policy) after having the ERO SHOULD perform an ERO expansion (unless not allowed by
computed the path to the next loose hop (ABR/ASBR) that obeys policy) after having computed the path to the next loose hop
the set of required constraints. If no path satisfying the set (ABR/ASBR) that obeys the set of required constraints. If no
of constraints can be found, the path computation stops and a path satisfying the set of constraints can be found, then this
Path Error MUST be sent for the inter-domain TE LSP. SHOULD be treated as a path computation and signaling failure
and a PathErr message SHOULD be sent for the inter-domain TE
LSP based on section 4.3.4 of [RSVP-TE].
b) Case of stitched or nested LSP b) Case of stitched or nested LSP
i) if the ABR/ASBR (receiving the LSP setup request) is i) If the boundary LSR is a candidate LSR for intra-
a candidate LSR for intra-area FA-LSP/LSP segment area H-LSP/S-LSP setup (the LSR has local policy for
setup, and if there is no FA-LSP/LSP segment from this nesting or stitching), and if there is no H-LSP/S-LSP
LSR to the next-hop boundary LSR (satisfying the from this LSR to the next-hop boundary LSR that
constraints) it SHOULD signal a FA-LSP/LSP segment to satisfies the constraints, it SHOULD signal a H-LSP/S-
the next-hop boundary LSR. If pre-configured FA-LSP(s) LSP to the next-hop boundary LSR. If pre-configured H-
LSP(s) or S-LSP(s) already exist, then it will try to
select from among those intra-domain LSPs. Depending on
local policy, it MAY signal a new H-LSP/S-LSP if this
selection fails. If the H-LSP/S-LSP is successfully
signaled or selected, it propagates the inter-domain
Path message to the next-hop following the procedures
described in [INTER-DOMAIN-SIG]. If, for some reason
the dynamic H-LSP/S-LSP setup to the next-hop boundary
LSR fails, then this SHOULD be treated as a path
Vasseur, Ayyangar and Zhang 8 Vasseur, Ayyangar and Zhang 8
or LSP segment(s) already exist, then it SHOULD try to computation and signaling failure and a PathErr message
select from among those intra-area/AS LSPs. Depending SHOULD be sent upstream for the inter-domain LSP.
on local policy, it MAY signal a new FA-LSP/LSP segment Similarly, if selection of a preconfigured H-LSP/S-LSP
if this selection fails. If the FA-LSP/LSP segment is fails and local policy prevents dynamic H-LSP/S this
successfully signaled or selected, it propagates the SHOULD be treated as a path computation and signaling
inter-domain Path message to the next-hop following the failure and a PathErr SHOULD be sent upstream for the
procedures described in [LSP-HIER]. If, for some reason inter-domain TE LSP. In both these cases procedures
the dynamic FA-LSP/LSP segment setup to the next-hop described in section 4.3.4 of [RSVP-TE] SHOULD be
boundary LSR fails, the path computation stops and a followed to handle the failure.
PathErr is sent upstream for the inter-domain LSP.
Similarly, if selection of a preconfigured FA-LSP/LSP
segment fails and local policy prevents dynamic FA-
LSP/LSP segment setup, then the path computation stops
and a PathErr is sent upstream for the inter-domain TE
LSP.
ii) If, however, the boundary LSR is not a FA-LSP/LSP
segment candidate, then it SHOULD simply compute a CSPF
path up to the next-hop boundary LSR carry out an ERO
expansion to the next-hop boundary LSR) and propagate
the Path message downstream. The outgoing ERO is
modified after the ERO expansion to the loose next-hop.
Note that in both cases, path computation may be ii) If, however, the boundary LSR is not a candidate
stopped due to some local policy. for intra-domain H-LSP/S-LSP (the LSR does not have
local policy for nesting or stitching), then it SHOULD
apply the same procedure as for the contiguous case.
4.1. Example with an inter-area TE LSP Note that in both cases, path computation and signaling
process may be stopped due to policy violation.
4.1.1. Case 1: T1 is a contiguous TE LSP The ERO of an inter-domain TE LSP may comprise abstract nodes such as
ASes. In such a case, upon receiving the ERO whose next hop is an AS,
the boundary LSR has to determine the next-hop boundary LSR which may
be determined based on the "auto-discovery" process mentioned above. If
multiple ASBRs candidates exist the boundary LSR may apply some
policies based on peering contracts that may have been pre-negotiated.
Once the next-hop boundary LSR has been determined a similar procedure
as the one described above is followed.
When the path message reaches ABR1, it first determines the egress LSR Note related to the inter-AS TE case
from its area 0 along the LSP path (say ABRĂ1), either directly from
the ERO (if for example the next hop ABR is specified as a loose hop in
the ERO) or by using some constraint-aware auto-discovery mechanism. In
the former case, every inter-AS TE LSP path is defined as a set of
loose and strict hops but at least the ABRs traversed by the inter-area
TE LSP MUST be specified as loose hops on the head-End LSR.
- Example 1 (set of strict hops end to end): R0-X1-ABR1-ABRĂ1-X2-X3-R1 The links interconnecting ASBRs are usually not TE-enabled and no IGP
- Example 2 (set of loose hops): R0-ABR1(loose)-ABRĂ1(loose)-R1(loose) is running at the AS boundaries. An implementation supporting inter-AS
- Example 3 (mix of strict and loose hops): R0-X1-ASBR1-ABRĂ1(loose)- MPLS TE MUST allow the set up of inter-AS TE LSP over the region
X2-X3-R1 interconnecting multiple ASBRs. In other words, an ASBR compliant with
this document MUST support the set up of TE LSP over inter-ASBR links
and MUST be able to perform all the usual operations related to MPLS
Traffic Engineering (call admission control, ...).
At least, the set of ABRs from the TE LSP head-end to the tail-End MUST In terms of computation of an inter-AS TE LSP path, an interesting
be present in the ERO as a set of loose hops. Optionally, a set of optimization technique consists of allowing the ASBRs to flood the TE
paths can be configured on the head-end LSR, ordered by priority. Each information related to the inter-ASBR link(s) although no IGP TE is
priority path can be associated with a different set of constraints. enabled over those links (and so there is no IGP adjacency over the
Typically, it might be desirable to systematically have a last resort inter-ASBR links). This of course implies for the inter-ASBR links to
option with no constraint to ensure that the inter-area TE LSP could be TE-enabled although no IGP is running on those links. This allows an
always be set up if at least a path exists between the inter-area TE LSR (could be entry ASBR) in the previous AS to make a more appropriate
route selection up to the entry ASBR in the immediately downstream AS
taking into account the constraints associated with the inter-ASBR
links. This reduces the risk of call set up failure due to inter-ASBR
links not satisfying the inter-AS TE LSP set of constraints. Note that
the TE information is only related to the inter-ASBR links: the TE
LSA/LSP flooded by the ASBR includes not only the TE-enabled links
contained in the AS but also the inter-ASBR links.
Vasseur, Ayyangar and Zhang 9 Vasseur, Ayyangar and Zhang 9
LSP source and destination. Note that in case of set up failure or when Note that no summarized TE information is leaked between ASes which is
an RSVP Path Error is received indicating the TE LSP has suffered a compliant with the requirements listed in [INT-AREA-REQS] and [INT-AS-
failure, an implementation might support the possibility to retry a REQS].
particular path option a specific amount of time (optionally with
dynamic intervals between each trial) before trying a lower priority
path option. Any path can be defined as a set of loose and strict hops.
In other words, in some cases, it might be desirable to rely on the
dynamic path computation in some area, and exert a strict control on
the path in other areas (defining strict hops).
Once it has computed the path up to the next ABR, ABR1 sends the Path For example, consider the diagram depicted in Figure 2: when ASBR1
message for the inter-area TE LSP to ABRĂ1. ABRĂ1 then repeats the a floods its IGP TE LSA ((opaque LSA for OSPF)/LSP (TLV 22 for IS-IS)) in
similar procedure and the Path message for the inter-area TE LSP will its routing domain, it reflects the reservation states and TE
reach the destination R1. If ABRĂ1 cannot find a path obeying the set properties of the following links: X1-ASBR1, ASBR1-ASBR2 and ASBR1-
of constraints for the inter-area TE LSP, the path computation stops ASBR4.
and ABRĂ1 MUST send a PathErr message to ABR1. Then ABR1 can in turn
triggers a new computation by selecting another egress boundary LSR
(ABRĂ2 in the example above) if crankback is allowed for this inter-
area TE LSP (see [CRANBACK]). If crankback is not allowed for that
inter-area TE LSP or if ABR1 has been configured not to perform
crankback, then ABR1 MUST stop any path computation for the TE LSP and
MUST forward a PathErr up to the head-end LSR (R0) without trying to
select another egress LSR.
4.1.2. Case 2: T1 is a stitched or nested TE LSP Thanks to such an optimization, the inter-ASBRs TE link information
corresponding to the links originated by the ASBR is made available in
the TED of other LSRs in the same domain that the ASBR belongs to.
Consequently, the path computation for an inter-AS TE LSP path can also
take into account the inter-ASBR link(s). This will improve the chance
of successful signaling along the next AS in case of resource shortage
or unsatisfied constraints on inter-ASBR links and it potentially
reduces one level of crankback. Note that no topology information is
flooded and these links are not used in IGP SPF computations. Only the
TE information for the outgoing links directly connected to the ASBR is
advertised.
When the path message reaches ABR1, ABR1 first determines the egress Note that an Operator may decide to operate a stitched segment or 1-hop
LSR from its area 0 along the LSP path (say ABRĂ1), either directly hierarchical LSP for the inter-ASBR link.
from the ERO or by using some constraint-aware auto-discovery
mechanism.
ABR1 will check if it has a FA-LSP or LSP segment to ABRĂ1 matching the 4.1. Example with an inter-area TE LSP
constraints carried in the inter-area TE LSP Path message. If not, ABR1
will compute the path for a FA-LSP or LSP segment from ABR1 to ABRĂ1
satisfying the constraint and will set it up accordingly. Note that the
FA-LSP or LSP segment could have also been pre-configured.
Once the ABR has selected the FA-LSP/LSP segment for the inter-area 4.1.1 Case 1: T1 is a contiguous TE LSP
LSP, using the signaling procedures described in [LSP-HIER], ABR1 sends
the Path message for inter-area TE LSP to ABRĂ1. Note that irrespective
of whether ABR1 does nesting or stitching, the Path message for the
inter-area TE LSP is always forwarded to ABRĂ1. ABRĂ1 then repeats the
exact same procedures and the Path message for the inter-area TE LSP
will reach the destination R1. If ABRĂ1 cannot find a path obeying the
set of constraints for the inter-area TE LSP, then ABRĂ1 MUST send a
PathErr message to ABR1. Then ABR1 can in turn either select another
FA-LSP/LSP segment to ABRĂ1 if such an LSP exists or select another
egress boundary LSR (ABRĂ2 in the example above) if crankback is
allowed for this inter-area TE LSP (see [CRANBACK]). If crankback is
not allowed for that inter-area TE LSP or if ABR1 has been configured
not to perform crankback, then ABR1 MUST forward a PathErr up to the
Vasseur, Ayyangar and Zhang 10 The Head-end LSR (R0) first determines the next hop ABR (which could be
manually configured by the user or dynamically determined by using
auto-discovery mechanism). R0 then computes the path to reach the
selected next hop ABR and signals the Path message. When the Path
message reaches ABR1, it first determines the next hop ABR from its
area 0 along the LSP path (say ABR3), either directly from the ERO (if
for example the next hop ABR is specified as a loose hop in the ERO) or
by using the auto-discovery mechanism specified above.
inter-area head-end LSR (R0) without trying to select another egress - Example 1 (set of loose hops): R0-ABR1(loose)-ABR3(loose)-R1(loose)
LSR. - Example 2 (mix of strict and loose hops): R0-X1-ASR1-ABR3(loose)-X2-
X3-R1
4.2. Example with an inter-AS TE LSP Note that a set of paths can be configured on the Head-end LSR, ordered
by priority. Each priority path can be associated with a different set
of constraints. It may be desirable to systematically have a last
resort option with no constraint to ensure that the inter-area TE LSP
could always be set up if at least a TE path exists between the inter-
area TE LSP source and destination. In case of set up failure or when
an RSVP PathErr is received indicating the TE LSP has suffered a
failure, an implementation might support the possibility to retry a
The procedures for establishing an inter-AS TE LSP are very similar to Vasseur, Ayyangar and Zhang 10
those of an inter-area TE LSP described above. The main difference is
related to the presence of inter-ASBRs link(s).
The links interconnecting ASBRs are usually not TE enabled and no IGP particular path option configurable amount of times (optionally with
is running at the AS boundaries. An implementation supporting inter-AS dynamic intervals between each trial) before trying a lower priority
MPLS TE MUST obviously allow the set up of inter-AS TE LSP over the path option.
region interconnecting multiple ASBRs. In other words, an ASBR
compliant with this document MUST support the set up of TE LSP over
ASBR to ASBR links, performing all the usual operations related to MPLS
Traffic Engineering (call admission control, Ó) as defined in [RSVP-
TE].
In term of computation of an inter-AS TE LSP path, an interesting Once it has computed the path up to the next hop ABR (ABR3), ABR1 sends
optimization consists of allowing the ASBRs to flood the TE information the Path message along the computed path. Upon receiving the Path
related to the inter-ASBR link(s) although no IGP TE is enabled over message, ABR3 then repeats a similar procedure. If ABR3 cannot find a
those links (and so there is no IGP adjacency over the inter-ASBR path obeying the set of constraints for the inter-area TE LSP, the
links). This of course implies for the inter-ASBR links to be TE- signaling process stops and ABR3 sends a PathErr message to ABR1. Then
enabled although no IGP is running on those links. This allows a head- ABR1 can in turn trigger a new path computation by selecting another
end LSR to make a more appropriate route selection up to the first ASBR egress boundary LSR (ABR4 in the example above) if crankback is allowed
in the next hop AS and will significantly reduce the number of for this inter-area TE LSP (see [CRANKBACK]). If crankback is not
signaling steps in route computation. This also allows the entry ASBR allowed for that inter-area TE LSP or if ABR1 has been configured not
in an AS to make a more appropriate route selection up to the entry to perform crankback, then ABR1 MUST stop the signaling process and
ASBR in the next hop AS taking into account constraints associated with MUST forward a PathErr up to the Head-end LSR (R0) without trying to
the ASBR-ASBR links. Moreover, this reduces the risk of call set up select another ABR.
failure due to inter-ASBR links not satisfying the inter-AS TE LSP set
of constraints. Note that the TE information is only related to the
inter-ASBR links: the TE LSA/LSP flooded by the ASBR includes not only
the TE-enabled links contained in the AS but also the inter-ASBR links.
Note that no summarized TE information is leaked between ASes which is 4.1.2 Case 2: T1 is a stitched or nested TE LSP
compliant with the requirements listed in [INTER-AREA-TE-REQS] and
[INTER-AS-TE-REQS].
Example: The Head-end LSR (R0) first determines the next hop ABR (which could be
manually configured by the user or dynamically determined by using
auto-discovery mechanism). R0 then computes the path to reach the
selected next hop ABR and signals the Path message. When the Path
message reaches ABR1, it first determines the next hop ABR from its
area 0 along the LSP path (say ABR3), either directly from the ERO (if
for example the next hop ABR is specified as a loose hop in the ERO) or
by using an auto-discovery mechanism, specified above.
<---BGP---> <---BGP--> ABR1 then checks if it has a H-LSP or S-LSP to ABR3 matching the
CE1---R0---X1-ASBR1-----ASBR4¨-R3---ASBR7-¨--ASBR9---R6 constraints carried in the inter-area TE LSP Path message. If not, ABR1
|\ \ | / | / | / | | | computes the path for a H-LSP or S-LSP from ABR1 to ABR3 satisfying the
| \ ASBR2---/ ASBR5 | -- | | | constraint and sets it up accordingly. Note that the H-LSP or S-LSP
| \ | | |/ | | | could have also been pre-configured.
R1-R2¨--ASBR3¨----ASBR6¨-R4---ASBR8¨---ASBR10---R7---CE2
For instance, in the diagram depicted above, when ASBR1 floods its IGP Once ABR1 has selected the H-LSP/S-LSP for the inter-area LSP, using
TE LSA (opaque LSA for OSPF)/LSP (TLV 22 for IS-IS) in its routing the signaling procedures described in [INTER-DOMAIN-SIG], ABR1 sends
the Path message for inter-area TE LSP to ABR3. Note that irrespective
of whether ABR1 does nesting or stitching, the Path message for the
inter-area TE LSP is always forwarded to ABR3. ABR3 then repeats the
exact same procedures. If ABR3 cannot find a path obeying the set of
constraints for the inter-area TE LSP, ABR3 sends a PathErr message to
ABR1. Then ABR1 can in turn either select another H-LSP/S-LSP to ABR3
if such an LSP exists or select another egress boundary LSR (ABR4 in
the example above) if crankback is allowed for this inter-area TE LSP
(see [CRANKBACK]). If crankback is not allowed for that inter-area TE
LSP or if ABR1 has been configured not to perform crankback, then ABR1
forwards the PathErr up to the inter-area Head-end LSR (R0) without
trying to select another egress LSR.
Vasseur, Ayyangar and Zhang 11 4.2. Example with an inter-AS TE LSP
domain, it reflects the reservation states and TE properties of the Vasseur, Ayyangar and Zhang 11
following links: X1-ASBR1, ASBR1-ASBR2 and ASBR1-ASBR4.
Thanks to such an optimization, the inter-ASBRs TE link information The path computation procedures for establishing an inter-AS TE LSP are
corresponding to the links originated by the ASBR is made available in very similar to those of an inter-area TE LSP described above. The main
the TED of other LSRs in the same area/AS that the ASBR belongs to. difference is related to the presence of inter-ASBRs link(s).
Consequently, the CSPF computation for an inter-AS TE LSP path can also
take into account the inter-ASBR link(s). This will improve the chance
of successful path computation up to the next AS in case of a
bottleneck on some inter-ASBR links and it potentially reduces one
level of crankback. Note that no topology information is flooded and
these links are not used in IGP SPF computations. Only the TE
information for the links originated by the ASBR is advertised.
4.2.1. Case 1: T1 is a contiguous TE LSP 4.2.1. Case 1: T1 is a contiguous TE LSP
The inter-AS TE path may be configured on the head-end LSR as a set of The inter-AS TE path may be configured on the Head-end LSR as a set of
strict hops, loose hops or a combination of both. strict hops, loose hops or a combination of both.
- Example 1 (set of strict hops end to end): R0-X1-ASBR1-ASBR4-ASBR5- - Example 1 (set of loose hops): ASBR4(loose)-ASBR9(loose)-R6(loose)
R3-ASBR7-ASBR9-R6 - Example 2 (mix of strict and loose hops): R2-ASBR3-ASBR2-ASBR1-ASBR4-
- Example 2 (set of loose hops): R0-ASBR4(loose)-ASBR9(loose)-R6(loose) ASBR10(loose)-ASBR9-R6
- Example 3 (mix of strict and loose hops): R0-R2-ASBR3-ASBR2-ASBR1-
ASBR4(loose)-ASBR10(loose)-ASBR9-R6
When a next hop is a loose hop, a dynamic path calculation (also called
ERO expansion) is required taking into account the topology and TE
information of its own AS and the set of TE LSP constraints. In the
example 1 above, the inter-AS TE LSP path is statically configured as a
set of strict hops; thus, in this case, no dynamic computation is
required. Conversely, in the example 2, a per-AS path computation is
performed, respectively on R0 for AS1, ASBR4 for AS2 and ASBR9 for AS3.
Note that when an LSR has to perform an ERO expansion, the next hop
must either belong to the same AS, or must be the ASBR directly
connected to the next hops AS. In this later case, the ASBR
reachability MUST be announced in the IGP TE LSA/LSP originated by its
neighboring ASBR. Indeed, in the example 2 above, the TE LSP path is
defined as: R0-ASBR4(loose)-ASBR9(loose)-R6(loose). This implies that
R0 must compute the path from R0 to ASBR4, hence the need for R0 to get
the TE reservation state related to the ASBR1-ASBR4 link (flooded in
AS1 by ASBR1). In addition, ASBR1 MUST also announce the IP address of
ASBR4 specified in the T1 path configuration.
If an auto-discovery mechanism is available, every LSR receiving an
RSVP Path message, will have to determine automatically the next hop
ASBR, based on the IGP/BGP reachability of the TE LSP destination. With
such a scheme, the head-end LSR and every downstream ASBR loose hop
(except the last loose hop that computes the path to the final
destination) automatically computes the path up to the next ASBR, the
next loose hop based on the IGP/BGP reachability of the TE LSP
destination. If a particular destination is reachable via multiple
Vasseur, Ayyangar and Zhang 12
loose hops (ASBRs), local heuristics may be implemented by the head-end In the example 1 above, a per-AS path computation is performed,
LSR/ASBRs to select the next hop an ASBR among a list of possible respectively on R0 for AS1, ASBR4 for AS2 and ASBR9 for AS3. Note that
choices (closest exit point, metric advertised for the IP destination when an LSR has to perform an ERO expansion, the next hop must either
(ex: OSPF LSA External - Type 2), local policy,...). Once the next ASBR belong to the same AS, or must be the ASBR directly connected to the
has been determined, an ERO expansion is performed as in the previous next hops AS. In this later case, the ASBR reachability is announced in
case. the IGP TE LSA/LSP originated by its neighboring ASBR. In the example 1
above, the TE LSP path is defined as: ASBR4(loose)-ASBR9(loose)-
R6(loose). This implies that R0 must compute the path from R0 to ASBR4,
hence the need for R0 to get the TE reservation state related to the
ASBR1-ASBR4 link (flooded in AS1 by ASBR1). In addition, ASBR1 must
also announce the IP address of ASBR4 specified in the T1's path
configuration.
Once it has computed the path up to the next ASBR, ASBR1 sends the Path Once it has computed the path up to the next hop ASBR, ASBR1 sends the
message for the inter-area TE LSP to ASBR4 (supposing that ASBR4 is the Path message for the inter-area TE LSP to ASBR4 (supposing that ASBR4
selected next hop ASBR). ASBR4 then repeats the exact same procedures is the selected next hop ASBR). ASBR4 then repeats the exact same
and the Path message for the inter-AS TE LSP will reach the destination procedures. If ASBR4 cannot find a path obeying the set of constraints
R1. If ASBR4 cannot find a path obeying the set of constraints for the for the inter-AS TE LSP, then ASBR4 sends a PathErr message to ASBR1.
inter-AS TE LSP, then ASBR4 MUST send a PathErr message to ASBR1. Then Then ASBR1 can in turn either select another ASBR (ASBR5 in the example
ASBR1 can in turn either select another ASBR (ASBR5 in the example
above) if crankback is allowed for this inter-AS TE LSP (see above) if crankback is allowed for this inter-AS TE LSP (see
[CRANBACK]). If crankback is not allowed for that inter-AS TE LSP or if [CRANKBACK]). If crankback is not allowed for that inter-AS TE LSP or
ASBR1 has been configured not to perform crankback, then ABR1 MUST stop if ASBR1 has been configured not to perform crankback, ABR1 stops the
the path computation and MUST forward a PathErr up to the head-end LSR signaling process and forwards a PathErr up to the Head-end LSR (R0)
(R0) without trying to select another egress LSR. In this case, the without trying to select another egress LSR. In this case, the Head-end
head-end LSR can in turn select another sequence of loose hops, if LSR can in turn select another sequence of loose hops, if configured.
configured. Alternatively, the head-end LSR may decide to retry the Alternatively, the Head-end LSR may decide to retry the same path; this
same path; this can be useful in case of set up failure due an outdated can be useful in case of set up failure due an outdated IGP TE database
IGP TE database in some downstream AS. An alternative could also be for in some downstream AS. An alternative could also be for the Head-end
the head-end LSR to retry to same sequence of loose hops after having LSR to retry to same sequence of loose hops after having relaxed some
relaxed some constraint(s). constraint(s).
4.2.2. Case 2: T1 is a stitched or nested TE LSP 4.2.2. Case 2: T1 is a stitched or nested TE LSP
The signaling procedures are very similar to the inter-area LSP setup The path computation procedures are very similar to the inter-area LSP
case described earlier. In this case, the FA-LSPs or LSP segments will setup case described earlier. In this case, the H-LSPs or S-LSPs are
only be originated by the ASBRs at the entry to the AS. originated by the ASBRs at the entry to the AS.
Vasseur, Ayyangar and Zhang 12
5. Path optimality/diversity 5. Path optimality/diversity
Since the inter-domain path is computed on a per domain (area, AS) Since the inter-domain TE LSP is computed on a per domain (area, AS)
basis, one cannot guarantee that the shortest inter-domain path can be basis, one cannot guarantee that the optimal inter-domain path can be
found. found.
Moreover, computing two diverse paths might not be possible in some Moreover, computing two diverse paths using a per-domain path
topologies (due to the well-known ˘trapping÷ problem). computation approach may not be possible in some topologies (due to the
well-known "trapping" problem).
As already pointed out, the required path computation method can be As already pointed out, the required path computation method can be
selected by the Operator on a per LSP basis. selected by the Service Provider on a per LSP basis.
6. MPLS Traffic Engineering Fast Reroute for inter-domain TE LSPs
The signaling aspects of Fast Reroute and related constraints for each
TE LSP types in the case of inter-domain TE LSP has been covered in
[INTER-DOMAIN-SIG] and will not be repeated in this document.
Vasseur, Ayyangar and Zhang 13
There are multiple failure scenarios to consider in the case of Fast
Reroute for inter-domain TE LSPs.
6.1. Failure of an internal network element
The case of a failure of a network element within an area/AS such as a
link, SRLG or a node does not differ from Fast Reroute for intra-domain
TE LSP.
6.2. Failure of an inter-ASBR links (inter-AS TE)
In order to protect inter-domain TE LSPs from the failure of an inter-
ASBR link, this requires the computation of a backup tunnel path that
crosses an non IGP TE-enabled region (between two ASes). If the inter-
ASBR TE related information is flooded in the IGPs, each ASBR is
capable of computing the path according to the backup tunnel
constraints. Otherwise, the backup tunnel path MUST be statically
configured.
6.3. Failure of an ABR or an ASBR node
The constraints to be taken into account during the backup tunnel path If the per-domain path computation technique does no meet the set of
computation significantly differs upon the TE LSP type, network element requirements for a particular TE LSP (e.g. path optimality,
to protect (entry/exit boundary node) and the Fast Reroute method in requirements for a set of diversely routed TE LSPs, ...) other techniques
use (facility backup versus one-to-one). Those constraints have been such as PCE-based path computation techniques may be used (see [PCE-
explored in detail in [INTER-DOMAIN-SIG] but since the backup tunnel is ARCH]).
itself an inter-domain TE LSP, its path computation can be performed
according to the two path computation methods described in this
document.
7. Reoptimization of an inter-domain TE LSP 6. Reoptimization of an inter-domain TE LSP
The ability to reoptimize an existing inter-domain TE LSP path is of The ability to reoptimize an already established inter-domain TE LSP
course a requirement. The reoptimization process significantly differs constitutes a requirement. The reoptimization process significantly
based upon the nature of the TE LSP and the mechanism in use for the TE differs based upon the nature of the TE LSP and the mechanism in use
LSP path computation. for the TE LSP computation.
The following mechanisms can be used for re-optimization, which are The following mechanisms can be used for reoptimization and are
dependent on the nature of the inter-domain TE LSP. dependent on the nature of the inter-domain TE LSP.
7.1. Contiguous TE LSPs 6.1. Contiguous TE LSPs
After an inter-AS TE LSP has been set up, a more optimal route might After an inter-domain TE LSP has been set up, a more optimal route
appear in the various traversed ASes. Then in this case, it is might appear within any traversed domain. Then in this case, it is
desirable to get the ability to reroute an inter-AS TE LSP in a non- desirable to get the ability to reroute an inter-domain TE LSP in a
disruptive fashion (making use of the so called Make Before Break non-disruptive fashion (making use of the so-called Make-Before-Break
procedure) to follow this more optimal path. This is a known as a TE procedure) to follow such more optimal path. This is a known as a TE
LSP reoptimization procedure. LSP reoptimization procedure.
[LOOSE-REOPT] proposes a mechanisms allowing: [LOOSE-REOPT] proposes a mechanism that allows the Head-end LSR to be
notified of the existence of a more optimal path in a downstream
Vasseur, Ayyangar and Zhang 14 domain. The Head-end LSR may then decide to gracefully reroute the TE
- The head-end LSR to trigger on every LSR whose next hop is a LSP using the so-called Make-Before-Break procedure.
loose hop the re evaluation of the current path in order to In case of a contiguous LSP, the reoptimization process is strictly
detect a potentially more optimal path. This is done via controlled by the Head-end LSR which triggers the make-before-break
explicit signaling request: the head-end LSR sets the ˘ERO procedure, regardless of the location of the more optimal path.
Expansion request÷ bit of the SESSION-ATTRIBUTE object carried
in the RSVP Path message.
- An LSR whose next hop is a loose-hop to signal to the head-
end LSR 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 be sent either:
- In response to a query sent by the head-end LSR,
- Spontaneously by any LSR having detected a more
optimal path
Such a mechanism allows for the reoptimization of a TE LSP if and only
if a better path is some downstream area/AS is detected.
The reoptimization event can either be timer or event-driven based (a
link UP event for instance).
Note that the reoptimization MUST always be performed in a non-
disruptive fashion.
Once the head-end LSR is informed of the existence of a more optimal 6.2. Stitched or nested (non-contiguous) TE LSPs
path either in its head-end area/AS or in another AS, the inter-AS TE
Path computation is triggered using the same set of mechanisms as when
the TE LSP is first set up. Then the inter-AS TE LSP is set up
following the more optimal path, making use of the make before break
procedure. In case of a contiguous LSP, the reoptimization process is
strictly controlled by the head-end LSR which triggers the make-before-
break procedure, regardless of the location where the more optimal path
is.
Note that in the case of loose hop reoptimization, the TE LSP may In the case of a stitched or nested inter-domain TE LSP, the
follow a preferable path within one or more domain(s) whereas in the reoptimization process is treated as a local matter to any domain. The
case of PCE-based path computation techniques, the reoptimization
process may lead to following a completely different inter-domain path
(including a different set of ABRs/ASBRs) since end-to-end shortest
path is computed.
7.2. Stitched or nested (non-contiguous) TE LSPs Vasseur, Ayyangar and Zhang 13
In the case of a stitched or nested inter-domain TE LSP, the re-
optimization process is treated as a local matter to any Area/AS. The
main reason is that the inter-domain TE LSP is a different LSP (and main reason is that the inter-domain TE LSP is a different LSP (and
therefore different RSVP session) from the intra-domain LSP segment or therefore different RSVP session) from the intra-domain S-LSP or H-LSP
FA-LSP in an area or an AS. Therefore, reoptimization in an area/AS is in an area or an AS. Therefore, reoptimization in a domain is done by
locally reoptimizing the intra-domain H-LSP or S-LSP. Since the inter-
Vasseur, Ayyangar and Zhang 15 domain TE LSPs are transported using S-LSP or H-LSP across each domain,
optimality of the inter-domain TE LSP in a domain is dependent on the
done by locally reoptimizing the intra-domain FA LSP or LSP segment. optimality of the corresponding S-LSP or H-LSPs. If, after an inter-
Since the inter-domain TE LSPs are transported using LSP segments or domain LSP is setup, a more optimal path is available within an domain,
FA-LSP across each domain, optimality of the inter-domain TE LSP in an the corresponding S-LSP or H-LSP will be reoptimized using "Make-
area/AS is dependent on the optimality of the corresponding LSP Before-Break" techniques discussed in [RSVP-TE]. Reoptimization of the
segments or FA-LSPs. If, after an inter-domain LSP is setup, a more H-LSP or S-LSP automatically reoptimizes the inter-domain TE LSPs that
optimal path is available within an area/AS, the corresponding LSP the H-LSP or the S-LSP transports. Reoptimization parameters like
segment(s) or FA-LSP will be re-optimized using "make-before-break" frequency of reoptimization, criteria for reoptimization like metric or
techniques discussed in [RSVP-TE]. Reoptimization of the FA LSP or LSP bandwidth availability, etc can vary from one domain to another and can
segment automatically reoptimizes the inter-domain TE LSPs that the LSP be configured as required, per intra-domain TE S-LSP or H-LSP if it is
segment transports. Reoptimization parameters like frequency of preconfigured or based on some global policy within the domain.
reoptimization, criteria for reoptimization like metric or bandwidth
availability; etc can vary from one area/AS to another and can be
configured as required, per intra-area/AS TE LSP segment or FA-LSP if
it is preconfigured or based on some global policy within the area/AS.
Hence, in this scheme, since each area/AS takes care of reoptimizing Hence, in this scheme, since each domain takes care of reoptimizing its
its own LSP segments or FA-LSPs, and therefore the corresponding inter- own S-LSPs or H-LSPs, and therefore the corresponding inter-domain TE
domain TE LSPs, the make-before-break can happen locally and is not LSPs, the Make-Before-Break can happen locally and is not triggered by
triggered by the head-end LSR for the inter-domain LSP. So, no the Head-end LSR for the inter-domain LSP. So, no additional RSVP
additional RSVP signaling is required for LSP re-optimization and signaling is required for LSP reoptimization and reoptimization is
reoptimization is transparent to the HE LSR of the inter-domain TE LSP. transparent to the Head-end LSR of the inter-domain TE LSP.
If, however, an operator desires to manually trigger reoptimization at If, however, an operator desires to manually trigger reoptimization at
the head-end LSR for the inter-domain TE LSP, then this solution does the Head-end LSR for the inter-domain TE LSP, then this solution does
not prevent that. A manual trigger for reoptimization at the head-end not prevent that. A manual trigger for reoptimization at the Head-end
LSR SHOULD force a reoptimization thereby signaling a "new" path for LSR SHOULD force a reoptimization thereby signaling a "new" path for
the same LSP (along the optimal path) making use of the make-before- the same LSP (along the more optimal path) making use of the Make-
break procedure. In response to this new setup request, the boundary Before-Break procedure. In response to this new setup request, the
LSR may either initiate new LSP segment setup, in case the inter-domain boundary LSR may either initiate new S-LSP setup, in case the inter-
TE LSP is being stitched to the intra-area/AS LSP segment or it may domain TE LSP is being stitched to the intra-domain S-LSP or it may
select an existing or new FA-LSP in case of nesting. When the LSP setup select an existing or new H-LSP in case of nesting. When the LSP setup
along the current optimal path is complete, the head end should along the current path is complete, the Head-end LSR should switchover
switchover the traffic onto that path and the old path is eventually the traffic onto that path and the old path is eventually torn down.
torn down. Note that the head-end LSR does not know a priori whether a Note that the Head-end LSR does not know a priori whether a more
more optimal path exists. Such a manual trigger from the head-end LSR optimal path exists. Such a manual trigger from the Head-end LSR of the
of the inter-domain TE LSP is, however, not considered to be a frequent inter-domain TE LSP is, however, not considered to be a frequent
occurrence. occurrence.
Note that stitching or nesting rely on local optimization: the Note that stitching or nesting rely on local optimization: the
reoptimization process allows to locally reoptimize each TE LSP segment reoptimization process allows to locally reoptimize each TE S-LSP
or FA-LSP: hence, the reoptimization is not global and consequently the or H-LSP: hence, the reoptimization is not global and consequently the
end to end path may no longer to optimal, should it be optimal when set end to end path may no longer be optimal should it be optimal when
up. being set up.
Procedures described in [LOOSE-REOPT] MUST be used if the operator does Procedures described in [LOOSE-REOPT] MUST be used if the operator does
not desire local re-optimization of certain inter-domain LSPs. In this not desire local reoptimization of certain inter-domain LSPs. In this
case, any re-optimization event within the domain MUST be reported to case, any reoptimization event within the domain MUST be reported to
the head-end node. This SHOULD be a configurable policy. the Head-end node. This SHOULD be a configurable policy.
8. Security Considerations Vasseur, Ayyangar and Zhang 14
6.3. Path characteristics after reoptimization
Vasseur, Ayyangar and Zhang 16 Note that in the case of loose hop reoptimization of contiguous inter-
domain TE LSP or local reoptimization of stitched/nested S-LSP where
boundary LSRs are specified as loose hops, the TE LSP may follow a
preferable path within one or more domain(s) but would still traverse
the same set of boundary LSRs. In contrast, in the case of PCE-based
path computation techniques, because end to end optimal path is
computed, the reoptimization process may lead to following a completely
different inter-domain path (including a different set of boundary
LSRs).
When signaling an inter-AS TE, an Operator may make use of the already 7. Security Considerations
defined security features related to RSVP (authentication). This may
require some coordination between Service Providers to share the keys
(see RFC 2747 and RFC 3097).
9. Intellectual Property Considerations Signaling of inter-domain TE LSPs raises security issues that have been
described in section 7 of [INTER-DOMAIN-SIG]; however the path
computation aspects specified in this document do not raise additional
security concerns.
8. Intellectual Property Considerations
The IETF takes no position regarding the validity or scope of any The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights 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 might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
skipping to change at line 858 skipping to change at line 768
assurances of licenses to be made available, or the result of an 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 attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at ietf- this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.. ipr@ietf.org.
IPR Disclosure Acknowledgement
By submitting this Internet-Draft, I certify that any applicable
patent or other IPR claims of which I am aware have been disclosed,
and any of which I become aware will be disclosed, in accordance with
RFC 3668.
10. Acknowledgments 9. Acknowledgments
We would like to acknowledge input and helpful comments from Adrian We would like to acknowledge input and helpful comments from Adrian
Farrel. Farrel, Jean-Louis Le Roux and Dimitri Papadimitriou.
11 References 10. References
Vasseur, Ayyangar and Zhang 15
10.1. Normative References 10.1. Normative References
[RFC] Bradner, S., "Key words for use in RFCs to indicate requirements [RFC2119] Bradner, S., "Key words for use in RFCs to indicate
levels", RFC 2119, March 1997. requirements levels", RFC 2119, March 1997.
[RFC3667] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC
3667, February 2004.
Vasseur, Ayyangar and Zhang 17
[RFC3668] Bradner, S., Ed., "Intellectual Property Rights in IETF [RFC3979] Bradner, S., Ed., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3668, February 2004. Technology", BCP 79, RFC 3979, March 2005.
[RSVP] Braden, et al, " Resource ReSerVation Protocol (RSVP) ű Version [RSVP] Braden, et al, "Resource ReSerVation Protocol (RSVP)" Version
1, Functional Specification÷, RFC 2205, September 1997. 1, Functional Specification", RFC 2205, September 1997.
[RSVP-TE] Awduche, et al, "Extensions to RSVP for LSP Tunnels", RFC [RSVP-TE] Awduche, et al, "Extensions to RSVP for LSP Tunnels", RFC
3209, December 2001. 3209, December 2001.
[REFRESH-REDUCTION] Berger et al, ˘RSVP Refresh Overhead Reduction
Extensions÷, RFC2961, April 2001.
[FAST-REROUTE] Ping Pan, et al, "Fast Reroute Extensions to RSVP-TE for
LSP Tunnels", draft-ietf-mpls-rsvp-lsp-fastreroute-03.txt, December
2003.
[OSPF-TE] Katz, D., Yeung, D., Kompella, K., "Traffic Engineering [OSPF-TE] Katz, D., Yeung, D., Kompella, K., "Traffic Engineering
Extensions to OSPF Version 2", RFC 3630, September 2003. Extensions to OSPF Version 2", RFC 3630, September 2003.
[ISIS-TE] Li, T., Smit, H., "IS-IS extensions for Traffic Engineering", [ISIS-TE] Li, T., Smit, H., "IS-IS extensions for Traffic Engineering",
RFC 3784, June 2004. RFC 3784, June 2004.
[G-OSPF]Rekhter Y., Kompella K, et al., "OSPF Extensions in Support of
Generalized Multi-Protocol Label Switching", draft-ietf-ccamp-ospf-
gmpls-extensions, work in progress.
[G-ISIS] Rekhter Y., Kompella K, et al., "IS-IS Extensions in Support
of Generalized Multi-Protocol Label Switching", draft-ietf-isis-gmpls-
extensions, work in progress.
10.2. Informative references 10.2. Informative references
[CRANKBACK] Farrel A., et al., "Crankback Signaling Extensions for MPLS
and GMPLS RSVP-TE", draft-ietf-ccamp-crankback, work in progress.
[INT-AREA-REQ] Le Roux, J.L., Vasseur, J.P., Boyle, J., "Requirements [INT-AREA-REQ] Le Roux, J.L., Vasseur, J.P., Boyle, J., "Requirements
for inter-area MPLS Traffic Engineering", draft-ietf-tewg-interarea- for inter-area MPLS Traffic Engineering", RFC 4105, June 2005.
mpls-te-req-03.txt, work in progress.
[INT-AS-REQ] Zhang, R., Vasseur, J.P., "MPLS Inter-AS Traffic [INT-AS-REQ] Zhang, R., Vasseur, J.P., "MPLS Inter-AS Traffic
Engineering Requirements", draft-ietf-tewg-interas-mpls-te-req-09.txt, Engineering Requirements", draft-ietf-tewg-interas-mpls-te-req, work in
work in progress. progress.
[INT-DOMAIN-FRWK] Farrel, A., Vasseur, J.P., Ayyangar, A., "A Framework [INT-DOMAIN-FRWK] Farrel, A., Vasseur, J.P., Ayyangar, A., "A Framework
for Inter-Domain MPLS Traffic Engineering", draft-ietf-ccamp-inter- for Inter-Domain MPLS Traffic Engineering", draft-ietf-ccamp-inter-
domain-framework-00.txt, work in progress. domain-framework, work in progress.
[FACILITY-BACKUP] Le Roux, J.L., Vasseur, J.P. et al. "Framework for Vasseur, Ayyangar and Zhang 16
PCE based MPLS Facility Backup Path Computation", draft-leroux-pce-
backup-comp-frwk-00.txt, work in progress
[INTER-DOMAIN-SIG] Ayyangar, A., Vasseur, JP. ˘Inter-domain MPLS [INTER-DOMAIN-SIG] Ayyangar, A., Vasseur, JP. "Inter-domain MPLS
Traffic Engineering ű RSVP extensions÷, draft-ietf-ccamp-inter-domain- Traffic Engineering - RSVP extensions", draft-ietf-ccamp-inter-domain-
rsvp-te, work in progress. rsvp-te, work in progress.
[LSP-STITCHING] Ayyangar, A., Vasseur, JP. ˘Label Switched Path [LSP-STITCHING] Ayyangar, A., Vasseur, JP. "Label Switched Path
Stitching with Generalized MPLS Traffic Engineering÷, draft-ietf-ccamp- Stitching with Generalized MPLS Traffic Engineering", draft-ietf-ccamp-
lsp-stitching-00, Work under progress. lsp-stitching-00, work under progress.
Vasseur, Ayyangar and Zhang 18
[LSP-ATTRIBUTE] Farrel A. et al, "Encoding of Attributes for
Multiprotocol Label Switching (MPLS) Label Switched Path (LSP)
Establishment Using RSVP-TE", draft-ietf-mpls-rsvpte-attributes-04,(work
in progress).
[GMPLS-OVERLAY] G. Swallow et al, "GMPLS RSVP Support for the Overlay
Model", (work in progress).
[EXCLUDE-ROUTE] Lee et all, Exclude Routes - Extension to RSVP-TE,
draft-ietf-ccamp-rsvp-te-exclude-route-00.txt, work in progress.
[LSPPING] Kompella, K., Pan, P., Sheth, N., Cooper, D.,Swallow, G.,
Wadhwa, S., Bonica, R., " Detecting Data Plane Liveliness in MPLS",
Internet Draft <draft-ietf-mpls-lsp-ping-02.txt>, October 2002. (Work
in Progress)
[MPLS-TTL], Agarwal, et al, "Time to Live (TTL) Processing in MPLS
Networks", RFC 3443 Updates RFC 3032) ", January 2003
[LOOSE-PATH-REOPT] Vasseur, Ikejiri and Zhang ˘Reoptimization of an
explicit loosely routed MPLS TE paths÷, draft-ietf-ccamp-loose-path-
reopt-01.txt, July 2004, Work in Progress.
[NODE-ID] Vasseur, Ali and Sivabalan, ˘Definition of an RRO node-id [LOOSE-PATH-REOPT] Vasseur, Ikejiri and Zhang "Reoptimization of an
subobject÷, draft-ietf-mpls-nodeid-subobject-05.txt, work in progress. explicit loosely routed MPLS TE paths", draft-ietf-ccamp-loose-path-
reopt, work in Progress.
[LSP-HIER] Kompella K., Rekhter Y., "LSP Hierarchy with Generalized [LSP-HIER] Kompella K., Rekhter Y., "LSP Hierarchy with Generalized
MPLS TE", draft-ietf-mpls-lsp-hierarchy-08.txt, March 2002. MPLS TE", draft-ietf-mpls-lsp-hierarchy-08.txt, March 2002.
[MPLS-TTL], Agarwal, et al, "Time to Live (TTL) Processing in MPLS [PCE-ARCH] Farrel A., Vasseur J.P, Ash J, "Path Computation Element
Networks", RFC 3443 (Updates RFC 3032) ", January 2003. (PCE) Architecture", draft-ietf-pce-architecture, work in progress.
Authors' Address: Authors' Address:
Jean-Philippe Vasseur (Editor) Jean-Philippe Vasseur (Editor)
Cisco Systems, Inc. Cisco Systems, Inc.
300 Beaver Brook Road 300 Beaver Brook Road
Boxborough , MA - 01719 Boxborough , MA - 01719
USA USA
Email: jpv@cisco.com Email: jpv@cisco.com
Arthi Ayyangar (Editor) Arthi Ayyangar (Editor)
Juniper Networks, Inc Juniper Networks, Inc
1194 N.Mathilda Ave 1194 N.Mathilda Ave
Sunnyvale, CA 94089 Sunnyvale, CA 94089
USA USA
e-mail: arthi@juniper.net e-mail: arthi@juniper.net
Vasseur, Ayyangar and Zhang 19
Raymond Zhang Raymond Zhang
Infonet Services Corporation BT/Infonet
2160 E. Grand Ave. 2160 E. Grand Ave.
El Segundo, CA 90025 El Segundo, CA 90025
USA USA
Email: raymond_zhang@infonet.com Email: raymond_zhang@infonet.com
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject to Copyright (C) The Internet Society (2005). This document is subject to
the rights, licenses and restrictions contained in BCP 78, and except the rights, licenses and restrictions contained in BCP 78, and except
as set forth therein, the authors retain all their rights. as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
Vasseur, Ayyangar and Zhang 17
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Vasseur, Ayyangar and Zhang 20 Vasseur, Ayyangar and Zhang 18
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