Network Working Group Tomonori Takeda
Internet Draft NTT
Proposed Status: Informational Yuichi Ikejiri
Expires: June 2007 NTT Communications
Adrian Farrel
Old Dog Consulting
Jean-Philippe Vasseur
Cisco Systems, Inc.
December 2006
Analysis of Inter-domain Label Switched Path (LSP) Recovery
draft-ietf-ccamp-inter-domain-recovery-analysis-00.txt
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Abstract
This document analyzes various schemes to realize Multiprotocol Label
Switching (MPLS) and Generalized MPLS (GMPLS) Label Switched Path
(LSP) recovery in multi-domain networks based on the existing
framework for multi-domain LSPs.
The main focus for this document is on establishing end-to-end
diverse Traffic Engineering (TE) LSPs in multi-domain networks. It
presents various diverse LSP setup schemes based on existing
functional elements.
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Table of Contents
1. Terminology....................................................2
2. Introduction...................................................3
2.1 Domain........................................................3
2.2 Document Scope................................................4
2.3 Note on Other Recovery Techniques.............................5
2.4 Signaling Options.............................................5
3. Diversity in Multi-domain Networks.............................5
3.1 Multi-domain Network Topology.................................6
3.2 Note on Domain Diversity......................................7
4. Factors to Consider............................................7
4.1 Scalability versus Optimality.................................7
4.2 Key Concepts..................................................8
5. Diverse LSP Setup Schemes without Confidentiality.............10
5.1 Management Configuration.....................................10
5.2 Head-end Path Computation (with multi-domain visibility).....10
5.3 Per-domain Path Computation..................................10
5.3.1 Sequential Path Computation................................11
5.3.2 Simultaneous Path Computation..............................11
5.4 Inter-domain Collaborative Path Computation..................12
5.4.1 Sequential Path Computation................................12
5.4.2 Simultaneous Path Computation..............................13
6. Diverse LSP Setup Schemes with Confidentiality................13
6.1 Management Configuration.....................................14
6.2 Head-end Path Computation (with multi-domain visibility).....14
6.3 Per-Domain Path Computation..................................15
6.3.1 Sequential Path Computation................................15
6.3.2 Simultaneous Path Computation..............................15
6.4 Inter-domain Collaborate Path Computation....................16
6.4.1 Sequential Path Computation................................16
6.4.2 Simultaneous Path Computation..............................16
7. Network Topology Specific Considerations......................17
8. Addressing Considerations.....................................17
9. Note on SRLG Diversity........................................17
10. Manageability Considerations.................................17
11. Security Considerations......................................18
12. References...................................................18
12.1 Normative References........................................18
12.2 Informative References......................................18
13. Acknowledgments..............................................20
14. Author's Addresses...........................................20
15. Intellectual Property Consideration..........................20
16. Full Copyright Statement.....................................21
1. Terminology
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The reader is assumed to be familiar with the terminology in [inter-
domain-fw] that provides a framework for inter-domain Label Switched
Path (LSP) setup, and [RFC4427] that provides terminology for LSP
recovery.
The following are several key terminologies used within this
document.
- Domain: See [inter-domain-fw]. A domain is considered to be any
collection of network elements within a common sphere of address
management or path computational responsibility. Note that nested
domains continue to be out of scope.
- Working LSP: See [RFC4427]. The working LSP transports normal user
traffic. Note that the term LSP and TE LSP will be used
interchangeably.
- Recovery LSP: See [RFC4427]. The recovery LSP transports normal
user traffic when the working LSP fails. The recovery LSP may
transport user traffic even when the working LSP is transporting
normal user traffic (e.g., 1+1 protection). In such a scenario,
the recovery LSP is sometimes referred to as a protecting LSP.
- Diversity: See [inter-domain-fw]. Diversity means the relationship
of multiple LSPs, where those LSPs do not share some specific type
of resource (e.g., link, node, or shared risk link group (SRLG)).
Diverse LSPs may be used for various purposes, such as load-
balancing and recovery. In this document, the recovery aspect of
diversity, specifically the end-to-end diversity of two traffic
engineering (TE) LSPs, is the focus. Those two diverse LSPs are
referred to as the working LSP and recovery LSP hereafter.
Sometimes, diversity is referred to as disjointness.
- Confidentiality: See [RFC4216]. The term confidentiality applies
to the protection of information about the topology and resources
present within one domain from visibility by people or
applications outside that domain.
2. Introduction
2.1 Domain
As defined in [inter-domain-fw], a domain is considered to be any
collection of network elements within a common sphere of address
management or path computational responsibility. Examples of such
domains include IGP areas and Autonomous Systems. A network accessed
over the Generalized Multiprotocol Label Switching (GMPLS) User-to-
Network Interface (UNI) [RFC4208] and a Layer One Virtual Private
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Network (L1VPNs) [L1VPN-FW] are special cases of multi-domain
networks.
Example objectives of domain usage include administrative separation,
scalability, and forming protection domains.
As described in [inter-domain-fw], there could be TE parameters (such
as color and priority) whose meanings are specific to each domain. In
such a scenarios, mapping functions could be performed based on
policy agreements between domain administrators.
2.2 Document Scope
This document analyzes various schemes to realize Multiprotocol Label
Switching (MPLS) and Generalized MPLS (GMPLS) LSP recovery in multi-
domain networks based on the existing framework for multi-domain LSP
setup [inter-domain-fw].
There are various recovery techniques for LSPs. For TE LSPs, major
techniques are end-to-end recovery [e2e-recovery], local protection
such as Fast Reroute (FRR) [RFC4090] (in packet switching
environments), and segment recovery [seg-recovery] (in GMPLS).
In this version of the document the main focus is the analysis of
diverse TE LSP (hereafter LSP) setup schemes, which can
advantageously used in the context of end-to-end recovery. This
document presents various diverse LSP setup schemes by combining
various functional elements. Analysis of other recovery techniques
could be added in a later revision of this document if necessary.
Furthermore, details of maintenance of diverse LSPs, such as re-
optimization and OAM, are for further study.
Note that the comparative evaluation of these various schemes is out
of scope for this document, and should be described in separate
applicability documents.
[RFC4105] and [RFC4216] describe requirements for diverse LSPs. There
could be various types of diversity, and this document focuses on
node/link/SRLG diversity. Note that domain diversity (that is, the
selection of paths that have only the ingress and egress domains in
common) is discussed in section 3.2.
Based on the service grade, both the working LSP and the recovery LSP
may be established at the time of service establishment (e.g.,
service requiring high resiliency). Alternatively, the recovery LSP
may be added later due to a change in the grade of the service.
Also, the recovery LSP may be used for 1+1 protection, 1:1
protection, or shared mesh restoration. However, ways to compute
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diverse paths, and the signaling of these TE LSPs are common across
all uses, and these topics are the main scope of this document.
Section 5 of [inter-domain-fw] describes some analysis of diverse
LSPs in multi-domain networks, and this document provides more
detailed analysis based on that content.
Note that diverse LSPs may be used for various purposes, in addition
to recovery. An example is for load-balancing, so as to limit the
traffic disruption to a portion of the traffic flow in case of a
single network element failure. This document does not preclude use
of diverse LSP setup schemes for those purposes.
2.3 Note on Other Recovery Techniques
Fast Reroute and segment recovery in multi-domain networks are
described in section 5.4 of [inter-domain-fw], and a more detailed
analysis is provided in section 5 of [inter-domain-rsvp]. Additional
analysis may be added in a future revision of this document if
necessary.
Also, the recovery type of an LSP or service may change at a domain
boundary. That is, the recovery type would remain the same within one
domain, but might be different in the next domain. This may be due to
the capabilities of each domain, administrative policies, or to
topology limitations. An example is where protection at the domain
boundary is provided by link protection on the inter-domain link(s),
but where protection within each domain is achieved through segment
recovery. This mixture of protection techniques is for further study.
2.4 Signaling Options
There are three signaling options for establishing inter-domain TE
LSPs: nesting, contiguous LSPs, and stitching [inter-domain-fw]. The
description in this document of diverse LSP setup is agnostic in
relation to the signaling option used, unless otherwise specified.
Note that signaling option specific considerations for Fast Reroute
and segment recovery are described in section 5 of [inter-domain-
rsvp]. Also note that if the recovery type changes at the domain
boundary, the nesting and stitching options may be more suitable.
Details are for further study.
3. Diversity in Multi-domain Networks
As described in section 2.2, analysis of diverse LSP setup schemes in
multi-domain networks is the main focus of this document. This
section describes some assumptions in this problem space made in this
document.
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3.1 Multi-domain Network Topology
Figures 1 and 2 show example multi-domain network topologies. In
Figure 1, domains are connected in a linear topology. There are
multiple paths between nodes A and L, but all of them cross domain#1-
domain#2-domain#3 in that order.
+--Domain#1--+ +--Domain#2--+ +--Domain#3--+
| | | | | |
| B------+---+---D-----E--+---+------J |
| / | | \ / | | \ |
| / | | \ / | | \ |
| A | | H | | L |
| \ | | / \ | | / |
| \ | | / \ | | / |
| C------+---+---F-----G--+---+------K |
| | | | | |
+------------+ +------------+ +------------+
Figure 1: Linear Connectivity
+-----Domain#2-----+
| |
| E--------------F |
| | | |
+-+--------------+-+
| |
+-Domain#1-+-+ +---------+--+
| | | | | |
| A-------B-+--+-C-------D |
| | | | | |
+--+---------+ +-+-Domain#4-+
| |
+-+--------------+-+
| | | |
| G--------------H |
| |
+-----Domain#3-----+
Figure 2: Mesh Connectivity
In Figure 2, domains are connected in a mesh topology. There are
multiple paths between nodes A and D, and these paths do not
necessarily follow the same set of domains.
Indeed, if inter-domain connectivity forms a mesh, domain level
routing is required (even for the unprotected case). This is tightly
coupled with the next hop domain resolution/discovery mechanisms.
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In this version of the document, we assume that domain level routing
is given via configuration or policy, and this is not part of path
computation process described later in this document. Details on more
advanced domain level routing are for further study.
In addition, domain level routing may perform "domain re-entry",
where a path enters a domain after the path exits that domain (e.g.,
domain#X-domain#Y-domain#X). This requires specific considerations
when confidentiality is required (described in section 4.2), and is
for further study.
Furthermore, the working LSP and the recovery LSP may or may not be
routed along the same set of domains in the same order. In this
version of the document, we assume that the working LSP and recovery
LSP follow the same set of domains in the same order (via
configuration or policy). Details on other scenarios are for further
study.
3.2 Note on Domain Diversity
As described in section 2.2, domain diversity means the selection of
paths that have only the ingress and egress domains in common. This
may provide enhanced resilience against failures, and is a way to
ensure path diversity for most of the path of the LSP.
In section 3.1 we assumed that the working LSP and the recovery LSP
follow the same set of domains in the same order. Under this
assumption, domain diversity cannot be achieved. However, by relaxing
this assumption, domain diversity could be achieved, e.g., by either
of the following schemes.
- Consider domain diversity as a special case of SRLG diversity
(i.e., assign an SRLG ID to each domain)
- Configure domain level routing to provide domain diverse paths
(e.g., by means of AS_PATH in BGP)
Details are for further study, should it been considered as a
requirement.
4. Factors to Consider
4.1 Scalability versus Optimality
As described in [inter-domain-fw], scalability and optimality are two
conflicting objectives. Note that the meaning of optimality differs
depending on each network operation. Some examples of optimality in
the context of diverse LSPs are:
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- Minimizing the sum of their cost while maintaining diversity
- Restricting the difference of their cost (so as to minimize delay
difference after switch-over) while maintaining diversity
By restricting TE information distribution to only within each domain
(and not across domain boundaries) as required by RFC4105 and
RFC4216, it may not be possible to compute an optimal path. As such,
it may not be possible to compute diverse paths, even if they exist.
However, if we assume domain level routing is given (as discussed in
section 3), it is possible to compute diverse paths in some schemes
if such paths exist. This is discussed in section 5.
4.2 Key Concepts
Three key concepts to classify various diverse LSP setup schemes are
presented below.
o With or without confidentiality
- Without confidentiality
Under this network configuration, it is possible to specify (by
means of the Explicit Route Object - ERO comprising a list of
strict hops) or obtain (by means of the recorded Route Object -
RRO) a route across other domains.
Examples of this configuration are multi-area networks, and some
forms of multi-AS networks (especially within the same provider).
- With confidentiality
Under this network configuration, it is not possible to specify
or obtain a route (by means of ERO/RRO) across other domains.
Paths may be specified/obtained in the form of ERO/RRO containing
loose hops. Therefore, it is not possible to specify or obtain a
full route at the head-end of a multi-domain LSP.
Examples of this configuration are some forms of multi-AS
networks (especially inter-provider networks), GMPLS-UNI
networks, and L1VPNs.
o Per domain path computation or inter-domain collaborative path
computation
- Per domain path computation
In this scheme, a path is computed domain by domain as LSP
signaling progresses through the network. This scheme requires
ERO expansion in each domain. The case for unprotected LSPs under
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this scheme is covered in [inter-domain-pd].
- Inter-domain collaborative path computation
In this scheme, path computation is typically done before
signaling. This scheme typically uses communication between
cooperating path computation elements (PCEs) [PCE-arch]. The case
for unprotected LSP under this scheme is covered in [brpc].
Note that these are path computation techniques. It is also
possible to obtain a path via management configuration, or head-end
path computation (with multi-domain visibility). This is also
discussed in sections 5 and 6.
Note also that it is possible to combine multiple path computation
techniques (including using a different technique for the working
and recovery LSPs), but this is for further study and is likely
to require sequential path computation (see below).
o Sequential path computation or simultaneous path computation
- Sequential path computation
The path of the working LSP is computed (without considering the
recovery LSP), and then the path of the recovery LSP is computed.
Typically, this scheme is applicable when the recovery LSP is
added later as change of the service grade. But this scheme can
also be applicable when both of the working and recovery LSPs are
established from the start. In this scheme, diverse LSPs may not
be correctly computed (without some form of re-optimization or
recomputation technique) in "trap" topologies. Furthermore, such
sequential path computation approach may prevent from finding an
"optimal" solution with regards to a specific objective function.
- Simultaneous path computation
The path of the working LSP and the path of the recovery LSP are
computed simultaneously. Typically, this scheme is applicable
when both the working LSP and the recovery LSP are established
together. In this scheme, it is possible to avoid trap
topologies. Furthermore it may allow for achieving more optimal
results.
Note that LSP setup with or without confidentiality is given as a
per-domain configuration, while the choices of per-domain path
computation or inter-domain collaborative path computation, and
sequential path computation or simultaneous path computation may be a
matter of choice for each individual pair of working/recovery LSPs.
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The analysis of various diverse LSP setup schemes is described in
sections 5 and 6, based on above criteria.
Some other considerations, such as network topology specific
considerations, addressing considerations, and SRLG diversity are
described in sections 7, 8 and 9.
5. Diverse LSP Setup Schemes without Confidentiality
In the following, various schemes for diverse LSP setup are presented
based on different path computation techniques assuming that there is
no requirement for confidentiality between domains. Section 6 makes a
similar examination of schemes where inter-domain confidentiality is
required.
5.1 Management Configuration
Section 3.1 of [inter-domain-fw] describes this path computation
technique. The full explicit paths for the working and recovery LSPs
are specified by a management application at the head-end, and no
further computation or signaling specific considerations are needed.
5.2 Head-end Path Computation (with multi-domain visibility)
Section 3.2.1 of [inter-domain-fw] describes this path computation
technique. The full explicit paths for the working and recovery LSPs
are computed at the head-end either by the head-end itself or by a
PCE. In either case the computing entity has full TE visibility
across multiple domains and no further computation or signaling
specific considerations are needed.
5.3 Per-domain Path Computation
Sections 3.2.2, 3.2.3 and 3.3 of [inter-domain-fw] describe this path
computation technique. More detailed procedures are described in
[inter-domain-pd].
In this scheme, the explicit paths of the working and recovery LSPs
are specified as the complete strict path in the source domain
followed by one of the following:
- The complete list of boundary LSRs (or domain identifiers, e.g., AS
numbers) along the path.
- The boundary LSR for the source domain and the LSP destination.
Thus, ERO expansion is needed at domain boundaries. Path computation
is performed by, or by a PCE on behalf of, each domain boundary LSR.
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For establishing diverse LSPs using per-domain computation, there are
two specific schemes, which are described in sections 5.3.1 and 5.3.2
respectively.
5.3.1 Sequential Path Computation
The Exclude Route Object (XRO) [XRO] can be used. Details are as
follows.
Assume that the working LSP is established as described in [inter-
domain-pd]. Also, assume that the route of the working LSP (full
route) is available at the head-end through the RRO.
o Path computation aspect
When performing path computation (ERO expansion) for the recovery
LSP as it crosses each domain boundary a path is selected that
avoids the nodes/links/SRLGs used by the working path so that a
diverse path is obtained.
o Signaling aspect
In order that the computation noted above can be performed, each
computation point must be aware of the path of the working LSP.
This information can be supplied in the XRO included in the Path
message for recovery LSP. The XRO lists nodes, links and SRLGs that
must be avoided by the LSP being signaled, and its contents are
copied from the RRO of the working LSP.
This scheme cannot guarantee to establish diverse LSPs (even if they
could exist) because the first LSP is established without
consideration of the need for a diverse recovery LSP. Crankback
[crankback] may be used in combination with this scheme in order to
improve the possibility of successful diverse LSP setup. Furthermore,
re-optimization of the working LSP and the recovery LSP may be used
to achieve fully diverse paths.
Note that even if a solution is found, the degree of optimality of
the solution (set of diverse TE LSP) might not be maximized.
5.3.2 Simultaneous Path Computation
o Path computation aspect
When signaling the working LSP, the path of not only the working
LSP, but also the recovery LSP is computed. For example, in
Figure 1, when node D receives a Path message for the working LSP
between nodes A and L, node D expands the ERO to reach domain#3. At
the same time, node D computes a path for the recovery LSP across
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the same domain from node F to reach domain#3. The entry boundary
node for the recovery LSP (node F) needs to be specified in the
Path message for the working LSP. In this example the path for the
working LSP may be computed by node D as D-E-domain#3, and the path
for recovery LSP as F-G-domain#3.
o Signaling aspect
There must be a mechanism to force the recovery LSP to follow the
route computed above. One way to realize this is to have a specific
object (with the same format as the ERO) to collect the route of
the recovery LSP in the Path message for the working LSP and to
return is to the head-end in the Resv message. When signaling the
recovery LSP, the content of the ERO is copied from this object.
This scheme also cannot guarantee to establish diverse LSPs (even if
they could exist) if there are more than two domain boundary nodes
out of each domain. Crankback [crankback] may also be used in
combination with this scheme to improve the chances of success.
Note that even if a solution is found, the degree of optimality of
the solution (set of diverse TE LSP) might not be maximized.
5.4 Inter-domain Collaborative Path Computation
Section 3.4 of [inter-domain-fw] describes this approach. [brpc]
provides some more detail. Path computation is performed for each of
the working and recovery LSPs by the use of inter-PCE communication
before each LSP is signaled.
There are two specific schemes for establishing diverse LSPs using
this scheme, which are described in sections 5.4.1 and 5.4.2.
5.4.1 Sequential Path Computation
Route exclusion using the XRO [XRO] can be requested in the PCE
communication protocol (PCEP) [PCEP] and this can be used to compute
the path of a recovery LSP after the path of the working LSP has been
determined. Details are as follows.
The working LSP is computed and may be immediately established as
described in [brpc]. Assume that the path of the working LSP (full
route) is available from the RRO.
o Path computation aspect
When requesting path computation for the recovery LSP, an XRO is
included in the PCEP path computation request message (see [PCEP]).
The content of the XRO is copied from the RRO of the working LSP.
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The computation request specifies that the full route must be
returned. Per-domain PCEs may need to be invoked by the first PCE
that is consulted in order to collaboratively determine the correct
path for the recovery LSP (just as described in [PCE-arch] and
[inter-domain-fw] for the computation of a single inter-domain LSP
by collaborating PCEs), and these PCEs exchange the XRO information
to ensure that the computed path is diverse from the working LSP.
o Signaling aspect
The recovery LSP is signaled by including an ERO whose content is
copied from the result returned by the PCE.
This scheme cannot guarantee to establish diverse LSPs (even if they
exist) because the working LSP may be blocking. In such a scenario,
re-optimization of the working and recovery LSPs may be used to
achieve fully diverse paths.
Note that PCEP [PCEP] does not currently include support for the XRO,
but that this is planned to be added in a future version.
5.4.2 Simultaneous Path Computation
o Path computation aspect
The PCEP SVEC Object allows diverse path computation to be
requested. It would be possible to extend [brpc] to compute diverse
paths. Details are for further study.
o Signaling aspect
In this scheme the PCE returns the full routes for the working and
recovery LSPs and they are signaled accordingly.
This scheme can guarantee to establish diverse LSPs (if they exist),
assuming domain level routing is given as described in section 3.
Furthermore, the computed set of TE LSPs may be optimal with respect
to some objective functions.
6. Diverse LSP Setup Schemes with Confidentiality
In the context of this section, the term confidentiality applies to
the protection of information about the topology and resources
present within one domain from visibility by people or applications
outside that domain. This includes, but is not limited to, recording
of LSP routes, in addition to advertisements of TE information. The
confidentiality does not apply to the protection of user traffic.
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Diverse LSP setup schemes with confidentiality are similar to ones
without confidentiality. However, several additional mechanisms are
needed to preserve confidentiality. Examples of such mechanisms are:
- Path key: Provide each per-domain segment of the path in advance to
the domain boundary nodes or to the PCE that computed the path for
a limited period of time (temporary caching) and identify it in the
signaled ERO using a path key. When path computation is done by
PCE, the identify of the PCE containing state for the path may be
required as well (e.g., PCE I-D). The path key is provided by the
PCE to the head-end for inclusion in the ERO [conf-segment].
- LSP segment: Pre-establish each per-domain segments of the path
using hierarchical LSPs [RFC4206] or LSP stitching segments
[LSP-stitch] and signal the end-to-end LSP to use these per-domain
LSPs. This scheme may need additional identifiers (such as LSP IDs)
in the Path message so that the domain boundary node can identify
which LSP segment or tunnel to use for the end-to-end LSP.
Furthermore, this scheme may require communication to pre-establish
the LSP segments.
These techniques may be directly applied, or may be applied with
extensions, depending on specific diverse LSP setup schemes described
below.
Note that in the schemes below, the paths of the working and recovery
LSPs are not impacted by the confidentiality requirements.
6.1 Management Configuration
It is not possible to obtain or specify the full explicit route for
either LSP at the head-end due to confidentiality restrictions.
Therefore, this information cannot be provided to signaling for LSP
setup.
Confidentially need not prevent the full computation of inter-domain
paths and signaling of sufficient information to distinguish the
paths. However the path information for each domain must be provided
in a way that does not have meaning to other domains. Example
mechanisms to preserve confidentiality as described above, include:
- Path key
- LSP segment
Details are for further study.
6.2 Head-end Path Computation (with multi-domain visibility)
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This scheme is not applicable since multi-domain visibility violates
confidentiality.
6.3 Per-Domain Path Computation
6.3.1 Sequential Path Computation
Assume the working LSP is established as described in [inter-domain-
pd].
It is not possible to obtain the route of the working LSP from the
RRO at the head-end due to confidentiality. In order to provide the
path of the working LSP through each domain to the computation point
responsible for computing the path of the protection LSP through each
domain additional mechanisms are needed. Examples of such mechanisms
are:
- Information identifying the working LSP is included in the Path
message for the recovery LSP, and the domain boundary node consults
the entity which computed the path of the working LSP (i.e., domain
boundary node or PCE), so that the diverse path can be computed.
When the entity which computed the path of the working LSP is the
PCE, PCE needs to be temporarily stateful. An example of such
information is the Association Object [e2e-recovery].
Details are for further study.
6.3.2 Simultaneous Path Computation
In this scheme the intention is to compute the path of the recovery
LSP at the same time as the working LSP. In order to force the
recovery LSP to follow the computed path as well as to preserve
confidentiality, additional mechanisms are needed to communicate the
computed recovery path from the path of the working LSP (where it was
computed) to the recovery LSP. Examples of such mechanisms, that must
continue to preserve confidentiality, are as follows.
- LSP segment: As described before. The LSP segment for the recovery
LSP is established domain-by-domain as the working LSP setup
progresses.
- Alternatively, information identifying the working LSP is included
in the Path message for the recovery LSP, and the domain boundary
node consults the entity which computed the path of the recovery
LSP (i.e., domain boundary node or PCE), so as to obtain the path
of the recovery LSP. This requires that the entity which computed
the path of the recovery LSP is temporarily stateful. An example of
such information is the Association Object [e2e-recovery].
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Details are for further study.
6.4 Inter-domain Collaborate Path Computation
6.4.1 Sequential Path Computation
Assume working LSP is established as described in [brpc].
It is not possible to obtain RRO of working LSP (full route) at the
head-end due to confidentiality.
o Path computation aspect
In order to obtain the path of the working LSP when computing the
path of the recovery LSP, additional mechanisms are needed.
Examples of such mechanisms are:
- Information identifying the working LSP is included in the PCEP
message when requesting path computation of the recovery LSP
should the PCE stateful (temporarily). An example of such
information is the Association Object [e2e-recovery].
o Signaling aspect
The full route for the recovery LSP can not be returned to the
head-end by PCE because it cannot be collected from the other PCEs
owing to confidentiality restrictions. In order to force the
recovery LSP to follow the path computed above, additional
mechanisms are needed. Examples of such mechanisms are as described
before:
- Path key
- LSP segment
Details are for further study.
6.4.2 Simultaneous Path Computation
It is not possible for PCE to return the full route of the working
LSP and recovery LSP to the head-end due to confidentiality. In order
to force the working and recovery LSPs to follow the paths computed,
additional mechanisms are needed. Examples of such mechanisms are as
described before:
- Path key: Use this for the working and recovery LSPs.
Note that the LSP segment approach in section 6 may not be applicable
here since a path cannot be determined until BRPC procedures are
completed.
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Details are for further study.
7. Network Topology Specific Considerations
In some specific network topologies, diverse LSP setup schemes
mentioned above could be drastically simplified.
For example, assume there are only three domains connected linearly,
and the first and the last domain contain only a single node. Assume
that we need to establish diverse LSPs from the node in the first
domain to the node in the last domain. In such a scenario, no BRPC
procedures are needed, because there is no need for path computation
in the first and last domains.
8. Addressing Considerations
All of the above-mentioned schemes are applicable when a single
address space is used across all domains.
However, there could be several cases where private addresses are
used within some of the domains. This case is similar to the one with
confidentiality, since the ERO and RRO are meaningless even if they
are available. Details are for further study.
9. Note on SRLG Diversity
The above-mentioned schemes are applicable when the nodes and links
in different domain belong to different SRLGs.
However, there could be several cases where the nodes and links in
different domain belong to the same SRLG. That is, where SRLGs span
domain boundaries. In such cases, in order to establish SRLG diverse
LSPs, several considerations are needed, such as:
- Record of the SRLGs used by the working LSP
- Indication of a set of SRLGs to exclude in the computation of the
recovery LSP's path.
Furthermore, SRLG IDs may be assigned independently in each domain,
and might not have global meaning. In such a scenario, some mapping
functions are necessary, similar to the mapping of other TE
parameters mentioned in section 2.1.
Details are for further study.
10. Manageability Considerations
TBD
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11. Security Considerations
TBD
12. References
12.1 Normative References
[inter-domain-fw] Farrel, A., et al., "A Framework for Inter-Domain
MPLS Traffic Engineering", draft-ietf-ccamp-
inter-domain-framework, work in progress.
[RFC4427] Mannie, E., Ed. and D. Papadimitriou, Ed.,
"Recovery (Protection and Restoration)
Terminology for Generalized Multi-Protocol Label
Switching (GMPLS)", RFC 4427, March 2006.
12.2 Informative References
[RFC4208] Swallow, G., et al., "Generalized Multiprotocol
Label Switching (GMPLS) User-Network Interface
(UNI): Resource ReserVation Protocol-Traffic
Engineering (RSVP-TE) Support for the Overlay
Model", RFC 4208, October 2005.
[L1VPN-FW] Takeda, T., Editor "Framework and Requirements
for Layer 1 Virtual Private Networks", draft-
ietf-l1vpn-framework, work in progress.
[PCE-arch] A. Farrel, JP. Vasseur and J. Ash, "Path
Computation Element (PCE) Architecture", draft-
ietf-pce-architecture, work in progress.
[e2e-recovery] Lang, J., Rekhter, Y., and Papadimitriou, D.
(Eds.), "RSVP-TE Extensions in support of End-to-
End Generalized Multi-Protocol Label Switching
(GMPLS)-based Recovery",
draft-ietf-ccamp-gmpls-recovery-e2e-signaling,
work in progress.
[RFC4090] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute
Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
May 2005.
[seg-recovery] Berger, L., Bryskin, I., Papadimitriou, D., and
Farrel, A., "GMPLS Based Segment Recovery",
draft-ietf-ccamp-gmpls-segment-recovery, work in
progress.
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[RFC4105] Le Roux, J.-L. , Vasseur, J.-P., and J. Boyle,
"Requirements for Inter-Area MPLS Traffic
Engineering", RFC 4105, June 2005.
[RFC4216] Zhang, R., and Vasseur, J.-P., "MPLS Inter-
Autonomous System (AS) Traffic Engineering (TE)
Requirements", RFC 4216, November 2005
[inter-domain-rsvp] Ayyangar, A., Vasseur, JP. "Inter-domain MPLS
Traffic Engineering - RSVP extensions", draft-
ietf-ccamp-inter-domain-rsvp-te, work in
progress.
[XRO] Lee et al., "Exclude Routes - Extension to
RSVP-TE", draft-ietf-ccamp-rsvp-te-exclude-route,
work in progress.
[inter-domain-pd] Vasseur JP., Ayyangar A., Zhang R., "A
per-domain path computation method for computing
Inter-domain Traffic Engineering Label Switched
Path", draft-ietf-ccamp-inter-domain-pd-path-
comp, work in progress.
[brpc] Vasseur, JP., Zhang, R., and Bitar, N., "A
Backward Recursive PCE-based Computation (BRPC)
procedure to compute shortest inter-domain
Traffic Engineering Label Switched Path", draft-
vasseur-ccamp-brpc, work in progress.
[PCEP] Vasseur, J., "Path Computation Element (PCE)
communication Protocol (PCEP) - Version 1 -",
draft-ietf-pce-pcep, work in progress.
[conf-segment] Bradford, R., Vasseur, JP., and Farrel, A.,
"Preserving Topology Confidentiality in Inter-
Domain Path Computation and Signaling", draft-
bradford-pce-path-key, work in progress.
[crankback] Farrel, A., et al., "Crankback Signaling
Extensions for MPLS Signaling", draft-ietf-
ccamp-crankback, work in progress.
[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched
Paths (LSP) Hierarchy with Generalized Multi-
Protocol Label Switching (GMPLS) Traffic
Engineering (TE)", RFC 4206, October 2005.
[LSP-stitch] Ayyangar, A., and Vasseur, JP., "LSP Stitching
T.Takeda, et al. Expires June 2007 [Page 19]
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with Generalized MPLS TE", draft-ietf-ccamp-lsp-
stitching, work in progress.
13. Acknowledgments
Authors would like to thank Eiji Oki, Ichiro Inoue and Kazuhiro
Fujihara for valuable comments.
14. Author's Addresses
Tomonori Takeda
NTT Network Service Systems Laboratories, NTT Corporation
3-9-11, Midori-Cho
Musashino-Shi, Tokyo 180-8585 Japan
Email : takeda.tomonori@lab.ntt.co.jp
Yuichi Ikejiri
NTT Communications Corporation
Tokyo Opera City Tower 3-20-2 Nishi Shinjuku, Shinjuku-ku
Tokyo 163-1421, Japan
Email: y.ikejiri@ntt.com
Adrian Farrel
Old Dog Consulting
Email: adrian@olddog.co.uk
Jean-Philippe Vasseur
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough , MA - 01719
USA
Email: jpv@cisco.com
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Copies of IPR disclosures made to the IETF Secretariat and any
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specification can be obtained from the IETF on-line IPR repository
T.Takeda, et al. Expires June 2007 [Page 20]
draft-ietf-ccamp-inter-domain-recovery-analysis-00.txt December 2006
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.
16. Full Copyright Statement
Copyright (C) The IETF Trust (2006).
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.
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,
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DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
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HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
T.Takeda, et al. Expires June 2007 [Page 21]
