wdiff rfc5441.original rfc5441.txt

Networking
Network Working Group JP. Vasseur, Ed.
Internet-Draft
Request for Comments: 5441 Cisco Systems, Inc
Intended status:
Category: Standards Track R. Zhang
Expires: October 16, 2008
BT Infonet
N. Bitar
Verizon
JL. Le Roux
France Telecom
April 14, 2008 2009

A Backward Recursive PCE-based Backward-Recursive PCE-Based Computation (BRPC) Procedure To to Compute
Shortest Constrained Inter-domain Inter-Domain Traffic Engineering
Label Switched Paths

draft-ietf-pce-brpc-09.txt

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Abstract

The ability to compute shortest constrained Traffic Engineering Label
Switched Paths (TE LSPs) in Multiprotocol Label Switching (MPLS) and
Generalized MPLS (GMPLS) networks across multiple domains (where has been
identified as a key requirement. In this context, a domain is a
collection of network elements within a common sphere of address
management or path computational responsibility such as an IGP area
or an Autonomous Systems) has been identified as a key
requirement. Systems. This document specifies a procedure
relying on the use of multiple Path Computation Elements (PCEs) to
compute such inter-
domain inter-domain shortest constrained paths across a
predetermined sequence of domains, using a backward recursive backward-recursive path
computation technique. This technique preserves confidentiality
across domains, which is sometimes required when domains are managed
by different Service
Providers.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. service providers.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3
3. General Assumptions . . . . . . . . . . . . . . . . . . . . . 5 4
4. BRPC Procedure . . . . . . . . . . . . . . . . . . . . . . . . 6 5
4.1. Domain Path Selection . . . . . . . . . . . . . . . . . . 7 6
4.2. Mode of Operation . . . . . . . . . . . . . . . . . . . . 7 6
5. PCEP Protocol Extensions . . . . . . . . . . . . . . . . . . . 9 8
6. VSPT Encoding . . . . . . . . . . . . . . . . . . . . . . . . 10 9
7. Inter-AS TE Links . . . . . . . . . . . . . . . . . . . . . . 10 9
8. Usage In in Conjunction With Per-domain with Per-Domain Path Computation . . . . 11 10
9. BRPC Procedure Completion Failure . . . . . . . . . . . . . . 11 10
10. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 12 10
10.1. Diverse end-to-end path computation End-to-End Path Computation . . . . . . . . . . . 12 11
10.2. Path Optimality . . . . . . . . . . . . . . . . . . . . . 12 11
11. Reoptimization Of An Inter-domain of an Inter-Domain TE LSP . . . . . . . . . . . 13 11
12. Path Computation Failure . . . . . . . . . . . . . . . . . . . 13 12
13. Metric Normalization . . . . . . . . . . . . . . . . . . . . . 13 12
14. Manageability Considerations . . . . . . . . . . . . . . . . . 14 12
14.1. Control of Function And and Policy . . . . . . . . . . . . . . 14 12
14.2. Information And and Data Models . . . . . . . . . . . . . . . 14 13
14.3. Liveness Detection and Monitoring . . . . . . . . . . . . 14 13
14.4. Verifying Correct Operation . . . . . . . . . . . . . . . 14 13
14.5. Requirements on Other Protocols and Functional
Components . . . . . . . . . . . . . . . . . . . . . . . . 15 13
14.6. Impact on Network Operation . . . . . . . . . . . . . . . 15 13
14.7. Path Computation Chain Monitoring . . . . . . . . . . . . 15 14
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 14
15.1. New Flag Of The of the RP Object . . . . . . . . . . . . . . . . 15 14
15.2. New Error-Type And and Error-Value . . . . . . . . . . . . . . 15 14
15.3. New Flag Of The of the NO-PATH-VECTOR TLV . . . . . . . . . . . . 16 15
16. Security Considerations . . . . . . . . . . . . . . . . . . . 16
17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16
18. References . . . . . . . . . . . 15
17. Acknowledgments . . . . . . . . . . . . . . . 16
18.1. Normative References . . . . . . . . 15
18. References . . . . . . . . . . . 16
18.2. Informative References . . . . . . . . . . . . . . . 16
18.1. Normative References . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . 16
18.2. Informative References . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . . . . 20 16

1. Introduction

The requirements for inter-area and inter-AS MPLS Traffic Engineering
(TE) have been developed by the Traffic Engineering Working Group (TE
WG) and have been stated in [RFC4105] and [RFC4216], respectively.

The framework for inter-domain Multiprotocol Label Switching (MPLS)
Traffic Engineering (TE) has been provided in [RFC4726].

[RFC5152] defines a technique for establishing an inter-domain
Generalized MPLS (GMPLS) TE Label Switched Path (LSP) whereby the
path is computed during the signalling signaling process on a per-domain basis
by the entry boundary node of each domain (each node responsible for
triggering the computation of a section of an inter-domain TE LSP
path is always along the path of such TE LSP). This path computation
technique fulfills some of the requirements stated in [RFC4105] and
[RFC4216] but not all of them. In particular, it cannot guarantee to
find an optimal (shortest) inter-domain constrained path.
Furthermore, it cannot be efficiently used to compute a set of inter-
domain diversely routed TE LSPs.

The Path Computation Element (PCE) architecture is defined in
[RFC4655]. The aim of this document is to describe a PCE-based path
computation procedure to compute optimal inter-domain constrained
(G)MPLS TE LSPs.

Qualifying a path as optimal requires some clarification. Indeed, a
globally optimal TE LSP placement usually refers to a set of TE LSPs
whose placements optimize the network resources with regards to a
specified objective function (e.g., a placement that reduces the
maximum or average network load while satisfying the TE LSP
constraints). In this document, an optimal inter-domain constrained
TE LSP is defined as the shortest path satisfying the set of required
constraints that would be obtained in the absence of multiple domains
(in other words, in a totally flat IGP network between the source and
destination of the TE LSP). Note that this requires to the use of
consistent metric schemes in each domain (see section Section 13).

1.1. Requirements Language

2. Terminology

ABR: Area Border Routers. Routers used to connect two IGP areas
(areas in OSPF or levels in IS-IS).

ASBR: Autonomous System Border Routers. Routers Router. Router used to connect
together ASes of the same or different Service Providers service providers via one or
more Inter-AS inter-AS links.

Boundary Node (BN): a boundary node is either an ABR in the context
of inter-area Traffic Engineering or an ASBR in the context of
inter-AS Traffic Engineering.

Entry BN of domain(n): a BN connecting domain(n-1) to domain(n) along
a determined sequence of domains.

Exit BN of domain(n): a BN connecting domain(n) to domain(n+1) along
a determined sequence of domains.

Inter-AS

Inter-area TE LSP: A TE LSP that crosses an AS IGP area boundary.

Inter-area

Inter-AS TE LSP: A TE LSP that crosses an IGP area AS boundary.

LSR: Label Switching Router.

LSP: Label Switched Path.

LSR: Label Switching Router.

PCC: Path Computation Client. Any client application requesting a
path computation to be performed by the a Path Computation Element.

PCE (Path

PCE: Path Computation Element): an Element. An entity (component, application application, or
network node) that is capable of computing a network path or route
based on a network graph and applying computational constraints.

PCE(i) is a PCE with the scope of domain(i).

TED: Traffic Engineering Database.

VSPT: Virtual Shortest Path Tree.

The notion of contiguous, stitched stitched, and nested TE LSPs is defined in
[RFC4726] and will not be repeated here.

3. General Assumptions

In the rest of this document, we make the following set of
assumptions common to inter-area and inter-AS MPLS TE:

o Each IGP area or Autonomous System (AS) is assumed to be Traffic
Engineering enabled.

o No topology or resource information is distributed between domains
(as mandated per [RFC4105] and [RFC4216]), which is critical to
preserve IGP/BGP scalability and confidentiality.

o While certain constraints like bandwidth can be used across
different domains, other TE constraints like (such as resource
affinity, color, metric, etc. as listed in [RFC2702] [RFC2702]) could be translated at
domain boundaries. If required, it is assumed that, at the domain
boundary nodes, there will exist some sort of local mapping based
on policy agreement, in order to translate such constraints across
domain boundaries during the inter-PCE communication process.

o Each AS can be made of several IGP areas. The path computation
procedure described in this document applies to the case of a
single AS made of multiple IGP areas, multiple ASes made of a
single IGP area area, or any combination of the above. For the sake of
simplicity, each AS will be considered to be made of a single area
in this document. The case of an Inter-AS inter-AS TE LSP spanning
multiple ASes ASes, where some of those ASes are themselves made of
multiple IGP areas areas, can be easily derived from this case by
applying the BRPC procedure described in this document,
recursively.

o The domain path (set (the set of domains traversed to reach the
destination domain) is either administratively pre-determined predetermined or
discovered by some means that is outside of the scope of this
document.

4. BRPC Procedure

The BRPC procedure is a Multiple-PCE multiple-PCE path computation technique as
described in [RFC4655]. A possible model consists of hosting the PCE
function on boundary nodes (e.g., ABR or ASBR) ASBR), but this is not
mandated by the BRPC procedure.

The BRPC procedure relies on communication between cooperating PCEs.
In particular, the PCC sends a PCReq to a PCE in its domain. The
request is forwarded between PCEs, domain-by-domain domain-by-domain, until the PCE
responsible for the domain containing the LSP destination is reached.
The PCE in the destination domain creates a tree of potential paths
to the destination (the Virtual Shortest Path Tree - VSPT) and passes
this back to the previous PCE in a PCRep. Each PCE in turn adds to
the VSPT and passes it back until the PCE in the source domain uses
the VSPT to select an end-to-end path that it the PCE sends to the PCC.

The BRPC procedure does not make any assumption with regards to the
nature of the inter-domain TE LSP that could be contiguous, nested nested,
or stitched.

Furthermore, no assumption is made on the actual path computation
algorithm in use by a PCE (e.g., it can be any variant of CSPF Constrained
Shortest Path First (CSPF) or an algorithm based on linear-programming linear
programming to solve multi-constraint optimization problems).

4.1. Domain Path Selection

The PCE-based BRPC procedure applies to the computation of an optimal
constrained inter-domain TE LSP. The sequence of domains to be
traversed is either administratively pre-determined predetermined or discovered by
some means that is outside of the scope of this document. The PCC
MAY indicate the sequence of domains to be traversed using the IRO
Include Route Object (IRO) defined in [I-D.ietf-pce-pcep] [RFC5440] so that it is
available to all PCEs. Note also that a sequence of PCEs MAY be
enforced by policy on the
PCC PCC, and this constraint can be carried in
the PCEP path computation request (as defined in [I-D.ietf-pce-monitoring]). [PCE-MONITOR]).

The BRPC procedure guarantees to compute the optimal path across a
specific sequence of traversed domains (which constitutes an
additional constraint). In the case of an arbitrary set of meshed
domains, the BRPC procedure can be used to compute the optimal path
across each domain set in order to get the optimal constrained path
between the source and the destination of the TE LSP. The BRPC
procedure can also be used across a subset of all domain sequences,
and the best path among these sequences can then be selected.

4.2. Mode of Operation

Definition of VSPT(i)

In each domain i:

o There is a set of X-en(i) entry BNs noted BN-en(k,i) where BN-
en(k,i)
BN-en(k,i) is the kth entry BN of domain(i).

o There is a set of X-ex(i) exit BNs noted BN-ex(k,i) where BN-
ex(k,i)
BN-ex(k,i) is the kth exit BN of domain(i).

VSPT(i): MP2P (MultiPoint To Point) (multipoint-to-point) tree returned by PCE(i) to
PCE(i-1):

Root (TE LSP destination)
/ I | \
BN-en(1,i) BN-en(2,i) ... BN-en(j,i).

Where

where [X-en(i)] is the number of entry BNs in domain i and j<= [X-en(i)]

Figure 1 - 1: MP2P Tree
Each link of tree VSPT(i) represents the shortest constrained path
between BN-en(j,i) and the TE LSP destination that satisfies the set
of required constraints for the TE LSP (bandwidth, affinities, ...). etc.).
These are path segments to reach the TE LSP destination from BN-
en(j,i).
BN-en(j,i).

Note that PCE(i) only considers the entry BNs of domain(i). That is domain(i), i.e.,
only the BNs that provide connectivity from domain(i-1). That is, In other
words, the set BN-en(k,i) is only made of those BNs that provide
connectivity from domain (i-1) to domain(i). Furthermore, some BNs
may be excluded according to policy constraints (either due to local
policy or policies signaled in the path computation request).

Step 1:
First, the PCC needs to first determine the PCE capable of serving its path
computation request (this can be done thanks to with local configuration or via
IGP discovery (see [RFC5088] and [RFC5089])). The path computation
request is then relayed until reaching a PCE(n) such that the TE LSP
destination resides in the domain(n). At each step of the process,
the next PCE can either be statically configured or dynamically
discovered via IGP/BGP extensions. If no next PCE can be found or
the next hop next-hop PCE of choice is unavailable, the procedure stops and a
path computation error is returned (see Section 9). If PCE(i-1)
discovers multiple PCEs for the adjacent domain(i), PCE(i) may select
a subset of these PCEs based on some local policies or heuristics.
The PCE selection process is outside of the scope of this document.

Step 2:
PCE(n) computes VSPT(n) VSPT(n), the tree made of the list of shortest
constrained paths between every BN-en(j,n) and the TE LSP destination
using a suitable path computation algorithm (e.g. (e.g., CSPF) and returns
the computed VSPT(n) to PCE(n-1).

Step i:

-
For i=n-1 to 2: PCE(i) computes VSPT(i), the tree made of the
shortest constrained paths between each BN-en(j,i) and the TE LSP
destination. It does this by considering its own TED and the
information in VSPT(i+1).

In the case of Inter-AS inter-AS TE LSP computation, this requires to also add requires adding
the inter-AS TE links connecting that connect the domain(i) to the domain(i+1).

Step n

Finally n:
Finally, PCE(1) computes the end-to-end shortest constrained path
from the source to the destination and returns the corresponding path
to the requesting PCC in the form of a PCRep message as defined in
[I-D.ietf-pce-pcep].
[RFC5440].

Each branch of the VSPT tree (path) may be returned in the form of an
explicit path (in which case case, all the hops along the path segment are
listed) or a loose path (in which case case, only the BN is specified) so
as to preserve confidentiality along with the respective cost. In
the later latter case, various techniques can be used in order to retrieve
the computed explicit paths on a per domain per-domain basis during the
signaling process process, thanks to the use of path keys as described in
[I-D.ietf-pce-path-key].
[PATH-KEY].

A PCE that can compute the requested path for more than one
consecutive domain on the path SHOULD perform this computation for
all such domains before passing the PCRep to the previous PCE in the
sequence.

BRPC guarantees to find the optimal (shortest) constrained inter-
domain TE LSP according to a set of defined domains to be traversed.
Note that other variants of the BRPC procedure relying on the same
principles are also possible.

Note also that in case of ECMP Equal Cost Multi-Path (ECMP) paths, more
than one path could be returned to the requesting LSR. PCC.

5. PCEP Protocol Extensions

The BRPC procedure requires the specification of a new flag of the RP
object carried within the PCReq message (defined in
[I-D.ietf-pce-pcep]) [RFC5440]) to
specify that the shortest paths satisfying the constraints from the
destination to the set of entry boundary nodes are requested (such a
set of paths forms the downstream VSPT as specified in Section 4.2).

The following new flag of the RP object is defined:

VSPT Flag

Bit Number Name Flag
7
25 VSPT

When set, the VSPT Flag indicates that the PCC requests the
computation of an inter-domain TE LSP using the BRPC procedure
defined in this document.

Because path segments computed by a downstream PCE in the context of
the BRPC procedure MUST be provided along with their respective path
costs, the C flag of the METRIC object carried within the PCReq
message MUST be set. It is the choice of the requester to
appropriately set the O bit of the RP object.

6. VSPT Encoding

The VSPT is returned within a PCRep message. The encoding consists
of a non-ordered lists list of EROs Explicit Route Objects (EROs) where each ERO
represents a path segment from a BN to the destination specified in
the END-POINT object of the corresponding PCReq message.

Example:

<---- area 1 ----><---- area 0 -----><------ area 2 ------>
ABR1-A-B-+
| |
ABR2-----D
| |
ABR3--C--+

Figure 2 - 2: An Example of VPST VSPT Encoding Using a Set of EROs

In the simple example shown in figure Figure 2, if we make the assumption
that a constrained path exists between each ABR and the destination
D, the VSPT computed by a PCE serving area 2 consists of the
following non-ordered set of EROs:

o ERO1: ABR1(TE Router ID)-A(Interface IP address)-B(Interface IP
address)-D(TE Router ID)

o ERO2: ABR2(TE Router ID)-D(TE Router ID)

o ERO3: ABR3(TE Router ID)-C(interface IP adress)-D(TE address)-D(TE Router ID)

The PCReq message, PCRep message, PCEP END-POINT object, and ERO objects
object are defined in [I-D.ietf-pce-pcep] [RFC5440].

7. Inter-AS TE Links

In the case of Inter-AS inter-AS TE LSP path computation, the BRPC procedure
requires the knowledge of the traffic engineering attributes of the
Inter-AS
inter-AS TE links: the links. The process by which the PCE acquires this
information is out of the scope of the BRPC procedure, which is
compliant with the PCE architecture defined in [RFC4655].

That said, a straightforward solution consists of allowing the ASBRs
to flood the TE information related to the inter-ASBR links although
no IGP TE is enabled over those links (there is no IGP adjacency over
the inter-ASBR links). This allows the PCE of a domain to get entire
TE visibility up to the set of entry ASBRs in the downstream domain
(see the IGP extensions defined in
[I-D.ietf-ccamp-isis-interas-te-extension] [RFC5316] and
[I-D.ietf-ccamp-ospf-interas-te-extension]). [RFC5392]).

8. Usage In in Conjunction With Per-domain with Per-Domain Path Computation

The BRPC procedure may be used to compute path segments in
conjunction with other path computation techniques (such as the per-
domain path computation technique defined in [RFC5152]) to compute
the end-to-end path. In this case case, end-to-end path optimality can no
longer be guaranteed.

9. BRPC Procedure Completion Failure

If the BRPC procedure cannot be completed because a PCE along the
domain does not recognize the procedure (VSPT flag of the RP object),
as stated in [I-D.ietf-pce-pcep], [RFC5440], the PCE sends a PCErr message to the upstream
PCE with an Error-Type=4 (not (Not supported object), Error-
value-4 Error-value=4
(Unsupported paramater). parameter). The PCE may include the parent object (RP
object) up to and including (but no further than) the unknown or
unsupported parameter. In this case where the unknown or unsupported
parameter is a bit flag (VSPT flag), the included RP object should
contain the whole bit flag field with all bits after the parameter at
issue set to zero. The corresponding path computation request is
then cancelled by the PCE without further notification.

If the BRPC procedure cannot be completed because a PCE along the
domain path recognises recognizes but does not support the procedure, it MUST
return a PCErr message to the upstream PCE with an Error-Type "BRPC
procedure completion failure".

The PCErr message MUST be relayed to the requesting PCC.

PCEP-ERROR objects are used to report a PCEP protocol error and are
characterized by an Error-Type which that specifies the type of error and
an Error-value that provides additional information about the error
type. Both the Error-Type and the Error-Value Error-value are managed by IANA.
A new Error-Type is defined that relates to the BRPC procedure.

Error-type

Error-Type Meaning
13 BRPC procedure completion failure
Error-value
1: BRPC procedure not supported by one or more PCEs
along the domain path

10. Applicability

As discussed in Section 3, the requirements for inter-area and
inter-AS MPLS Traffic Engineering have been developed by the Traffic
Engineering Working Group (TE WG) and have been stated in [RFC4105]
and [RFC4216], respectively. Among the set of requirements, both
documents indicate the need for some solution providing that provides the
ability to compute an optimal (shortest) constrained inter-domain TE
LSP and to compute a set of diverse inter-domain TE LSPs.

10.1. Diverse end-to-end path computation End-to-End Path Computation

PCEP (see [I-D.ietf-pce-pcep]) [RFC5440]) allows a PCC to request the computation of a set
of diverse TE LSPs thanks to the SVEC object by setting the SVEC object's flags L, N N, or S to
request link, node node, or SRLG diversity (Shared Risk Link Group) diversity,
respectively. Such requests MUST be taken into account by each PCE
along the path computation chain during the VSPT computation. In the
context of the BRPC procedure, a set of diversely routed TE LSPs
between two LSRs can be computed since the paths path segments of the VSPT
are simultaneously computed by a given PCE. The BRPC procedure
allows for the computation of diverse paths under various objective
functions (such as minimizing the sum of the costs of the N diverse
paths, etc). etc.).

By constrast, contrast, with a 2-step approach consisting of computing the first
path followed by the computation of computing the second path after having removed the
set of network elements traversed by the first path (if that does not
violate confidentiality preservation), one cannot guarantee that a
solution will be found even if such solution exists. Furthermore,
even if a solution is found, it may not be the most optimal one with
respect to an objective function such as minimizing the sum of the paths
paths' costs, bounding the path delays of both paths paths, and so on.
Finally, it must be noted that such a 2-step path computation
approach is usually less efficient in term terms of
signalling signaling delays since
it requires that two serialized TE LSP LSPs be set up.

10.2. Path Optimality

BRPC guarantees that the optimal (shortest) constrained inter-domain
path will always be found found, subject to policy constraints. When
combined with other Both in
the case where local path computation techniques (e.g. in the
case of stitched/nested are used (such as to
build stitched or nested TE LSP) LSPs), and in the case where a domain has
more than one BN-en or more than one BN-ex, it is only possible to
guarantee optimality after some network change within the domain can only be guaranteed by re-
executing
completely re-executing the BRPC procedure.

11. Reoptimization Of An Inter-domain of an Inter-Domain TE LSP

The ability to reoptimize an existing inter-domain TE LSP path has
been explicitly listed as a requirement in [RFC4105] and [RFC4216].
In the case of a TE LSP reoptimization request, the reoptimization
procedure defined in [I-D.ietf-pce-pcep] [RFC5440] applies where when the path in use (if
available on the head-end) is provided as part of the path
computation request in order for so that the PCEs involved in the reoptimization
request to can avoid double bandwidth accounting.

12. Path Computation Failure

If a PCE requires to relay a path computation request according to
the BRPC procedure defined in this document to a downstream PCE and
no such PCE is available, the PCE MUST send a negative path
computation reply to the requester using a PCReq message as specified
in [I-D.ietf-pce-pcep] [RFC5440] that contains a NO-PATH object. In such case, the
NO-PATH object MUST carry a NO-PATH-VECTOR TLV (defined in
[I-D.ietf-pce-pcep]) [RFC5440])
with the newly defined bit named "BRPC Path
Computation path computation chain
unavailable" set.

Bit number Name Flag
4
28 BRPC Path path computation chain unavailable

13. Metric Normalization

In the case of inter-area TE, the same IGP/TE metric scheme is
usually adopted for all the IGP areas (e.g., based on the link-speed,
propagation delay delay, or some other combination of link attributes).
Hence, the proposed set of mechanisms always computes the shortest
path across multiple areas obeying that obey the required set of constraints
with respect to a specified objective function. Conversely, in the
case of Inter-AS inter-AS TE, in order for this path computation to be
meaningful, metric normalization between ASes may be required. One
solution to avoid IGP metric modification would be for the Service
Providers service
providers to agree on a TE metric normalization scheme and use the TE
metric for TE LSP path computation (in that case, this the use of the TE
metric must be requested in the PCEP Path path computation request) using
the METRIC object (defined in [I-D.ietf-pce-pcep]). [RFC5440]).

14. Manageability Considerations

This section follows the guidance of
[I-D.ietf-pce-manageability-requirements]. [PCE-MANAGE].

14.1. Control of Function And and Policy

The only configurable item is the support of the BRPC procedure on a
PCE. The support of the BRPC procedure by the PCE MAY be controlled
by a policy module governing the conditions under which a PCE should
participate to in the BRPC procedure (origin of the requests, number of
requests per second, ...). etc.). If the BRPC is not supported/allowed on
a PCE, it MUST send a PCErr message as specified in Section 9.

14.2. Information And and Data Models

A BRPC MIB module will be specified in a separate document.

14.3. Liveness Detection and Monitoring

The BRPC procedure is a Multiple-PCE multiple-PCE path computation technique and and,
as such such, a set of PCEs are involved in the path computation chain.
If the path computation chain is not operational either because at
least one PCE does not support the BRPC procedure or because one of
the PCEs that must be involved in the path computation chain is not
available, procedures are defined to report such failures in
Section Sections
9 and Section 12 12, respectively. Furthermore, a built-in diagnostic tool to
check the availability and performances of a PCE chain is defined in [I-D.ietf-pce-monitoring].
[PCE-MONITOR].

14.4. Verifying Correct Operation

Verifying the correct operation of BRPC can be performed by
monitoring a set of parameters. A BRPC implementation SHOULD provide
the following parameters:

o Number of successful BRPC Procedure procedure completions on a per PCE peer
basis, per-PCE-peer
basis

o Number of BRPC procedure completion failures because the VSPT flag
was not recognized (on a per PCE peer basis), per-PCE-peer basis)

o Number of BRPC procedure completetion completion failures because the BRPC
procedure was not supported (on a per PCE peer basis), per-PCE-peer basis)

14.5. Requirements on Other Protocols and Functional Components

The BRPC procedure does not put any new requirements on other
protocol.
protocols. That said, since the BRPC procedure relies on the PCEP
protocol, there is a dependency between BRPC and PCEP; consequently consequently,
the BRPC procedure inherently makes use of the management functions
developed for PCEP.

14.6. Impact on Network Operation

The BRPC procedure does not have any significant impact on network
operation: indeed, BRPC is a Multiple-PCE multiple-PCE path computation scheme as
defined in [RFC4655] and does not differ from any other path
computation request.

14.7. Path Computation Chain Monitoring

[I-D.ietf-pce-monitoring]

[PCE-MONITOR] specifies a set of mechanisms that can be used to
gather PCE state metrics. Because BRPC is a Multiple-PCE multiple-PCE path
computation techniques, technique, such mechanism mechanisms could be advantageously used
in the context of the BRPC procedure to check the liveness of the
path computation chain, locate a faulty component, monitor the
overall performance performance, and so on.

15. IANA Considerations

15.1. New Flag Of The of the RP Object

A new flag of the RP object (specified in [I-D.ietf-pce-pcep]) [RFC5440]) is defined in
this document.

VSPT IANA maintains a registry of RP object flags in the
"RP Object Flag Field" sub-registry of the "Path Computation Element
Protocol (PCEP) Numbers" registry.

IANA has allocated the following value:

Bit Number Name Flag Description Reference
7

25 VSPT This document

15.2. New Error-Type And and Error-Value

IANA maintains a registry of Error-Types and Error-values for use in
PCEP messages. This is maintained as the "PCEP-ERROR Object Error
Types and Values" sub-registry of the "Path Computation Element
Protocol (PCEP) Numbers" registry.

A new Error-value is defined for the Error-Type "Not supported
object" (type 4).

Error-Type Meaning and error values Reference

4 Not supported object

Error-value=4: Unsupported parameter This document

A new Error-Type is defined in this document (Error-Type and Error-
value to be assigned by IANA).

Error-type as follows:

Error-Type Meaning Reference

13 BRPC procedure completion failure This document
Error-value
1:

Error-value=1: BRPC procedure not This document
supported by one a PCE or more PCEs along
the domain path

15.3. New Flag Of The of the NO-PATH-VECTOR TLV

A new flag of the NO-PATH-VECTOR TLV defined in [I-D.ietf-pce-pcep]) [RFC5440]) is
specified in this document.

IANA maintains a registry of flags for the NO-PATH-VECTOR TLV in the
"NO-PATH-VECTOR TLV Flag Field" sub-registry of the "Path Computation
Element Protocol (PCEP) Numbers" registry.

IANA has allocated the following allocation value:

Bit number Meaning Reference

4 BRPC Path path computation This document
chain unavailable

16. Security Considerations

The BRPC procedure relies on the use of the PCEP protocol and as such
is subjected to the potential attacks listed in section 11 Section 10 of
[I-D.ietf-pce-pcep].
[RFC5440]. In addition to the security mechanisms described in [I-D.ietf-pce-pcep]
[RFC5440] with regards to spoofing, snooping,
falsification falsification, and Denial
denial of Service, service, an implementation MAY support a policy module
governing the conditions under which a PCE should participate to in the
BRPC procedure.

The BRPC procedure does not increase the information exchanged
between ASes and preserves topology confidentiality, in compliance
with [RFC4105] and [RFC4216].

17. Acknowledgements Acknowledgments

The authors would like to thank Arthi Ayyangar, Dimitri
Papadimitriou, Siva Sivabalan, Meral Shirazipour Shirazipour, and Mach Chen for
their useful comments. A special thank thanks to Adrian Farrel for his
useful comments and suggestions.

18. References

18.1. Normative References

[I-D.ietf-pce-pcep]
Ayyangar, A., Oki, E., Atlas, A., Dolganow, A., Ikejiri,
Y., Kumaki, K., Vasseur, J., and J. Roux, "Path
Computation Element (PCE) Communication Protocol (PCEP)",
draft-ietf-pce-pcep-12 (work in progress), March 2008.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC5440] Vasseur, J., Ed. and J. Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)",
RFC 5440, April 2009.

18.2. Informative References

[I-D.ietf-ccamp-isis-interas-te-extension]
Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
Support of Inter-AS Multiprotocol Label Switching (MPLS)
and Generalized MPLS (GMPLS) Traffic Engineering",
draft-ietf-ccamp-isis-interas-te-extension-02 (work in
progress), April 2008.

[I-D.ietf-ccamp-ospf-interas-te-extension]
Chen, M., Zhang,

[PATH-KEY] Bradford, R., and X. Duan, "OSPF Extensions in
Support of Inter-AS Multiprotocol Label Switching (MPLS)
and Generalized MPLS (GMPLS) Traffic Engineering",
draft-ietf-ccamp-ospf-interas-te-extension-05 (work Vasseur, J., and A. Farrel, "Preserving
Topology Confidentiality in
progress), April Inter-Domain Path
Computation Using a Key-Based Mechanism", Work in
Progress, November 2008.

[I-D.ietf-pce-manageability-requirements]

[PCE-MANAGE] Farrel, A., "Inclusion of Manageability Sections in
PCE Working Group Drafts",
draft-ietf-pce-manageability-requirements-03 (work Work in
progress), February 2008.

[I-D.ietf-pce-monitoring] Progress,
January 2009.

[PCE-MONITOR] Vasseur, J., Roux, J., and Y. Ikejiri, "A set of
monitoring tools for Path Computation Element based
Architecture", draft-ietf-pce-monitoring-01 (work in
progress), February 2008.

[I-D.ietf-pce-path-key]
Bradford, R. and J. Vasseur, "Preserving Topology
Confidentiality Work in Inter-Domain Path Computation Using a
Key-Based Mechanism", draft-ietf-pce-path-key-02 (work in
progress), February Progress, November 2008.

[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and
J. McManus, "Requirements for Traffic Engineering Over
MPLS", RFC 2702, September 1999.

[RFC4105] Le Roux, J., Vasseur, J., and J. Boyle, "Requirements
for Inter-Area MPLS Traffic Engineering", RFC 4105,
June 2005.

[RFC4216] Zhang, R. and J. Vasseur, "MPLS Inter-Autonomous
System (AS) Traffic Engineering (TE) Requirements",
RFC 4216, November 2005.

[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture",
RFC 4655, August 2006.

[RFC4726] Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework
for Inter-Domain Multiprotocol Label Switching Traffic
Engineering", RFC 4726, November 2006.

[RFC5088] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
"OSPF Protocol Extensions for Path Computation Element
(PCE) Discovery", RFC 5088, January 2008.

[RFC5089] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang,
"IS-IS Protocol Extensions for Path Computation
Element (PCE) Discovery", RFC 5089, January 2008.

[RFC5152] Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain Per-
Domain Path Computation Method for Establishing Inter-Domain Inter-
Domain Traffic Engineering (TE) Label Switched Paths
(LSPs)", RFC 5152, February 2008.

[RFC5316] Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
Support of Inter-Autonomous System (AS) MPLS and GMPLS
Traffic Engineering", RFC 5316, December 2008.

[RFC5392] Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
Support of Inter-Autonomous System (AS) MPLS and GMPLS
Traffic Engineering", RFC 5392, January 2009.

Authors' Addresses

JP Vasseur (editor)
Cisco Systems, Inc
1414 Massachusetts Avenue
Boxborough, MA 01719
USA

Email:

EMail: jpv@cisco.com

Raymond Zhang
BT Infonet
2160 E. Grand Ave.
El Segundo, CA 90025
USA

Email: raymond_zhang@bt.infonet.com

EMail: raymond.zhang@bt.com

Nabil Bitar
Verizon
40 Sylvan Road
117 West Street
Waltham, MA 02145 02451
USA

Email: nabil.bitar@verizon.com

EMail: nabil.n.bitar@verizon.com
JL Le Roux
France Telecom
2, Avenue Pierre-Marzin
Lannion, 22307
FRANCE

Email: jeanlouis.leroux@orange-ft.com

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