rfc5376
Network Working Group N. Bitar
Request for Comments: 5376 Verizon
Category: Informational R. Zhang
BT
K. Kumaki
KDDI R&D Labs
November 2008
Inter-AS Requirements for the
Path Computation Element Communication Protocol (PCECP)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
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Abstract
Multiprotocol Label Switching Traffic Engineered (MPLS TE) Label
Switched Paths (LSPs) may be established wholly within an Autonomous
System (AS) or may cross AS boundaries.
The Path Computation Element (PCE) is a component that is capable of
computing constrained paths for (G)MPLS TE LSPs. The PCE
Communication Protocol (PCECP) is defined to allow communication
between Path Computation Clients (PCCs) and PCEs, as well as between
PCEs. The PCECP is used to request constrained paths and to supply
computed paths in response. Generic requirements for the PCECP are
set out in "Path Computation Element (PCE) Communication Protocol
Generic Requirements", RFC 4657. This document extends those
requirements to cover the use of PCECP in support of inter-AS MPLS
TE.
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Table of Contents
1. Introduction ....................................................3
2. Terminology .....................................................3
3. Reference Model .................................................4
3.1. Scope of Deployment Model ..................................5
4. Detailed PCECP Requirements for Inter-AS G(MPLS) TE Path
Computation .....................................................6
4.1. PCE Communication Protocol Requirements ....................6
4.1.1. Requirements for Path Computation Requests ..........6
4.1.2. Requirements for Path Computation Responses .........7
4.2. Scalability and Performance Considerations .................8
4.3. Management Considerations ..................................8
4.4. Confidentiality ............................................9
4.5. Policy Controls Affecting Inter-AS PCECP ...................9
4.5.1. Inter-AS PCE Peering Policy Controls ...............10
4.5.2. Inter-AS PCE Re-Interpretation Policies ............10
5. Security Considerations ........................................10
5.1. Use and Distribution of Keys ..............................11
5.2. Application of Policy .....................................11
5.3. Confidentiality ...........................................12
5.4. Falsification of Information ..............................12
6. Acknowledgments ................................................12
7. Normative References ...........................................13
8. Informative References .........................................13
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1. Introduction
[RFC4216] defines the scenarios motivating the deployment of inter-AS
Multiprotocol Label Switching Traffic Engineering (MPLS TE) and
specifies the requirements for inter-AS MPLS TE when the ASes are
under the administration of one Service Provider (SP) or the
administration of different SPs.
Three signaling options are defined for setting up an inter-AS TE
Label Switched Path (LSP):
1) contiguous TE LSP as documented in [RFC5151];
2) stitched inter-AS TE LSP discussed in [RFC5150];
3) nested TE LSP as in [RFC4206].
[RFC5152] defines mechanisms for the computation of inter-domain TE
LSPs using network elements along the signaling paths to compute
per-domain constrained path segments. The mechanisms in [RFC5152] do
not guarantee an optimum constrained path across multiple ASes where
an optimum path for a TE LSP is one that has the smallest cost,
according to a normalized TE metric (based upon a TE metric or
Interior Gateway Protocol (IGP) metric adopted in each transit AS)
among all possible paths that satisfy the LSP TE constraints.
The Path Computation Element (PCE) [RFC4655] is a component that is
capable of computing paths for MPLS TE and Generalized Multiprotocol
Label Switching Protocol ((G)MPLS TE) LSPs. The requirements for a
PCE have come from SP demands to compute optimum constrained paths
across multiple areas and/or domains, and to be able to separate the
path computation elements from the forwarding elements.
The PCE Communication Protocol (PCECP) is defined to allow
communication between Path Computation Clients (PCCs) and PCEs, and
between PCEs. The PCECP is used to request (G)MPLS TE paths and to
supply computed paths in response. Generic requirements for the
PCECP are discussed in [RFC4657]. This document provides a set of
PCECP requirements that are specific to inter-AS (G)MPLS TE path
computation.
2. Terminology
This document adopts the definitions and acronyms defined in Section
3 of [RFC4216] and Section 2 of [RFC4655]. In addition, we use the
following terminology:
ASBR: Autonomous System Border Router (see section 3 of RFC 4216)
PCECP: PCE Communication Protocol
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(G)MPLS TE: MPLS or Generalized MPLS Traffic Engineering
Inter-AS (G)MPLS TE path: An MPLS TE or Generalized MPLS (GMPLS) path
that traverses two or more ASes.
Intra-AS (G)MPLS TE path: An MPLS TE or GMPLS path that is confined
to a single AS. It may traverse one or more IGP areas.
Intra-AS PCE: A PCE responsible for computing (G)MPLS TE paths
remaining within a single AS.
Inter-AS PCE: A PCE responsible for computing inter-AS (G)MPLS paths
or path segments, possibly by cooperating with intra-AS PCEs.
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.
3. Reference Model
Figure 1 depicts the reference model for PCEs in an inter-AS
application. We refer to two types of PCE functions in this
document: inter-AS PCEs and intra-AS PCEs. Inter-AS PCEs perform the
procedures needed for inter-AS (G)MPLS TE path computation while
intra-AS PCEs perform the functions needed for intra-AS (G)MPLS TE
path computation.
Inter-AS Inter-AS Inter-AS
PCC <-->PCE1<--------->PCE2<---------------->PCE3
:: :: :: ::
:: :: :: ::
R1----ASBR1====ASBR3---R3---ASBR5====ASBR7---R5---R7
| | | | | |
| | | | | |
R2----ASBR2====ASBR4---R4---ASBR6====ASBR8---R6---R8
::
::
Intra-AS
PCE
<==AS1==> <=====AS2=====> <====AS3====>
Figure 1: Inter- and Intra-AS PCE Reference Model
Let's follow a scenario that illustrates the interaction among PCCs,
inter-AS PCEs, and intra-AS PCEs, as shown in Figure 1. R1 in AS1
wants to setup a (G)MPLS TE path, call it LSP1, with certain
constraints to R7 in AS3. R1 determines, using mechanisms out of the
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scope of this document, that R7 is an inter-AS route and that R1
(itself) needs to contact its Inter-AS PCE1 to compute the path. R1,
as a PCC, sends a PCECP path computation request to PCE1. PCE1
determines that R7 is reachable via AS2 and that PCE2 is the PCE to
ask for path computation across AS2. PCE1 sends a PCECP path
computation request to PCE2. Inter-AS PCE2, in turn, sends a PCECP
path computation request to Intra-AS PCE R4 to compute a path within
AS2 (in certain cases, the same router such as R3 can assume both
inter-AS and intra-AS path computation functions). R4 may for
instance return a PCECP path computation response to PCE2 with ASBR3
as the entry point to AS2 from AS1 and ASBR7 as the exit point to
AS3. PCE2 then sends a PCECP path computation request to PCE3 to
compute the path segment across AS3, starting at ASBR7 and
terminating at R7. PCE3 returns a PCECP path computation response to
PCE2 with the path segment ASBR7-R7. PCE2 then returns path ASBR3-
ASBR5-ASBR7-R7 to PCE1, which, in turn, returns path ASBR1-ASBR3-
ASBR5-ASBR7-R7 to PCC R1.
As described in the above scenario, in general, a PCC may contact an
inter-AS PCE to request the computation of an inter-AS path. That
PCE may supply the path itself or may solicit the services of other
PCEs, which may themselves be inter-AS PCEs, or may be intra-AS PCEs
with the responsibility for computing path segments within just one
AS.
This document describes the PCE Communication Protocol requirements
for inter-AS path computation, i.e., for PCCs to communicate path
computation requests for inter-AS (G)MPLS TE paths to PCEs, and for
the PCEs to respond. It also includes the requirements for PCEs to
communicate inter-AS path computation requests and responses.
3.1. Scope of Deployment Model
All attempts to predict future deployment scopes within the Internet
have proven fruitless. Nevertheless, it may be helpful to provide
some discussion of the scope of the inter-AS deployment model as
envisioned at the time of writing.
It is expected that most, if not all, inter-AS PCECP-based
communications will be between PCEs operating in the cooperative PCE
model described in [RFC4655]. Clearly, in this model, the requesting
PCE acts as a PCC for the purpose of issuing a path computation
request, but nevertheless, the requesting node fills the wider role
of a PCE in its own AS. It is currently considered unlikely that a
PCC (for example, a normal Label Switching Router) will make a path
computation request to a PCE outside its own AS. This means that the
PCECP relationships between ASes are limited to at most n squared
(n^2), where n is the number of peering PCEs in the various ASes
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(considered to be no greater than 100 in [RFC4657]). In practice,
however, it is likely that only a few PCEs in one AS will be
designated for PCECP communications with a PCE in an adjacent AS, and
each of these will only have a few PCEs in the adjacent AS to choose
from. A deployment model might place the PCEs as co-resident with
the ASBRs, resulting in a manageable scaling of the PCE-PCE
relationships. Scaling considerations (Section 4.2), manageability
considerations (Section 4.3), and security considerations (Section 5)
should be examined in the light of these deployment expectations.
4. Detailed PCECP Requirements for Inter-AS G(MPLS) TE Path Computation
This section discusses detailed PCECP requirements for inter-AS
(G)MPLS TE LSPs. Depending on the deployment environment, some or
all of the requirements described here may be utilized.
Specifically, some requirements are more applicable to inter-
provider inter-AS (G)MPLS TE operations than to intra-provider
operations.
4.1. PCE Communication Protocol Requirements
Requirements specific to inter-AS PCECP path computation requests and
responses are discussed in the following sections.
4.1.1. Requirements for Path Computation Requests
The following are inter-AS specific requirements for PCECP requests
for path computation:
1. [RFC4657] states the requirement for a priority level to be
associated with each path computation request. This document does
not change that requirement. However, PCECP should include a
mechanism that enables an inter-AS PCE to inform the requesting
inter-AS PCE of a change in the request priority level that may
have resulted from the application of a local policy.
2. A path computation request by an inter-AS PCE or a PCC to another
inter-AS PCE MUST be able to specify the sequence of ASes and/or
ASBRs across the network by providing ASBRs and/or ASes as hops in
the desired path of the TE LSP to the destination. For instance,
an inter-AS PCE MUST be able to specify to the inter-AS PCE
serving the neighboring AS a preferred ASBR for exiting to that AS
and reach the destination. That is, where multiple ASBRs exist,
the requester MUST be able to indicate a preference for one of
them. The PCE must be able to indicate whether the specified ASBR
or AS is mandatory or non-mandatory on the (G)MPLS TE path.
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3. PCECP MUST allow a requester to provide a list of ASes and/or
ASBRs to be excluded from the computed path.
4. A PCECP path computation request from one inter-AS PCE to another
MUST include the AS number of the requesting AS to enable the
correct application of local policy at the second inter-AS PCE.
5. A path computation request from a PCC to an inter-AS PCE or an
inter-AS PCE to another MUST be able to specify the need for
protection against node, link, or Shared Risk Link Group (SRLG)
failure using 1:1 detours or facility backup. It MUST be possible
to request protection across all ASes or across specific ASes.
6. PCECP MUST support the disjoint path requirements as specified in
[RFC4657]. In addition, it MUST allow the specification of AS-
diversity for the computation of a set of two or more paths.
7. A PCECP path computation request message MUST be able to identify
the scope of diversified path computation to be end-to-end (i.e.,
between the endpoints of the (G)MPLS TE tunnel) or to be limited
to a specific AS.
4.1.2. Requirements for Path Computation Responses
The following are inter-AS specific requirements for PCECP responses
for path computation:
1. A PCECP path computation response from one inter-AS PCE to another
MUST be able to include both ASBRs and ASes in the computed path
while preserving path segment and topology confidentiality.
2. A PCECP path computation response from one inter-AS PCE to the
requesting inter-AS PCE MUST be able to carry an identifier for a
path segment it computes to preserve path segment and topology
confidentiality. The objective of the identifier is to be
included in the TE LSP signaling, whose mechanism is out of scope
of this document, to be used for path expansion during LSP
signaling.
3. If a constraint for a desired ASBR (see Section 4.1.1, requirement
2) cannot be satisfied by a PCE, PCECP SHOULD allow the PCE to
notify the requester of that fact as an error in a path
computation response.
4. A PCECP path computation response from an inter-AS PCE to a
requesting inter-AS PCE or a PCC MUST be able to carry a
cumulative inter-AS path cost. Path cost normalization across
ASes is out of scope of this document.
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5. A PCECP path computation response from an inter-AS PCE to a PCC
SHOULD be able to carry the intra-AS cost of the path segment
within the PCC AS.
6. A PCECP path computation response MUST be able to identify
diversified paths for the same (G)MPLS TE LSP. End-to-end (i.e.,
between the two endpoints of the (G)MPLS TE tunnel) disjoint paths
are paths that do not share nodes, links, or SRLGs except for the
LSP head-end and tail-end. In cases where diversified path
segments are desired within one or more ASes, the disjoint path
segments may share only the ASBRs of the first AS and the ASBR of
the last AS across these ASes.
4.2. Scalability and Performance Considerations
PCECP design for use in the inter-AS case SHOULD consider the
following criteria:
- PCE message processing load.
- Scalability as a function of the following parameters:
o number of PCCs within the scope of an inter-AS PCE
o number of intra-AS PCEs within the scope of an inter-AS PCE
o number of peering inter-AS PCEs per inter-AS PCE
- Added complexity caused by inter-AS features.
4.3. Management Considerations
[RFC4657] specifies generic requirements for PCECP management. This
document specifies new requirements that apply to inter-AS
operations.
The PCECP MIB module MUST provide objects to control the behavior of
PCECP in inter-AS applications. These objects include the ASes
within the scope of an inter-AS PCE, inter-AS PCEs in neighboring
ASes to which the requesting PCE will or will not communicate,
confidentiality, and policies.
The built-in diagnostic tools MUST enable failure detection and
status checking of PCC/PCE-PCE PCECP. Diagnostic tools include
statistics collection on the historical behavior of PCECP as
specified in [RFC4657], but additionally it MUST be possible to
analyze these statistics on a neighboring AS basis (i.e., across the
inter-AS PCEs that belong to a neighboring AS).
The MIB module MUST support trap functions when thresholds are
crossed or when important events occur as stated in [RFC4657]. These
thresholds SHOULD be specifiable per neighbor AS as well as per peer
inter-AS PCE, and traps should be accordingly generated.
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Basic liveliness detection for PCC/PCE-PCE PCECP is described in
[RFC4657]. The PCECP MIB module SHOULD allow control of liveliness
check behavior by providing a liveliness message frequency MIB
object, and this frequency object SHOULD be specified per inter-AS
PCE peer. In addition, there SHOULD be a MIB object that specifies
the dead-interval as a multiplier of the liveliness message frequency
so that if no liveliness message is received within that time from an
inter-AS PCE, the inter-AS PCE is declared unreachable.
4.4. Confidentiality
Confidentiality mainly applies to inter-provider (inter-AS) PCE
communication. It is about protecting the information exchanged
between PCEs and about protecting the topology information within an
SP's network. Confidentiality rules may also apply among ASes owned
by a single SP. Each SP will in most cases designate some PCEs for
inter-AS (G)MPLS TE path computation within its own administrative
domain and some other PCEs for inter-provider inter-AS (G)MPLS TE
path computation. Among the inter-provider-scoped inter-AS PCEs in
each SP domain, there may also be a subset of the PCEs specifically
enabled for path computation across a specific set of ASes of
different peer SPs.
PCECP MUST allow an SP to hide from other SPs the set of hops within
its own ASes that are traversed by an inter-AS inter-provider TE LSP
(c.f., Section 5.2.1 of [RFC4216]). In a multi-SP administrative
domain environment, SPs may want to hide their network topologies for
security or commercial reasons. Thus, for each inter-AS TE LSP path
segment an inter-AS PCE computes, it may return to the requesting
inter-AS PCE an inter-AS TE LSP path segment from its own ASes
without detailing the explicit intra-AS hops. As stated earlier,
PCECP responses SHOULD be able to carry path-segment identifiers that
replace the details of that path segment. The potential use of that
identifier for path expansion, for instance, during LSP signaling is
out of scope of this document.
4.5. Policy Controls Affecting Inter-AS PCECP
Section 5.2.2 of [RFC4216] discusses the policy control requirements
for inter-AS RSVP-TE signaling at the AS boundaries for the
enforcement of interconnect agreements, attribute/parameter
translation and security hardening.
This section discusses those policy control requirements that are
similar to what are discussed in section 5.2.2 of [RFC4216] for
PCECP. Please note that SPs may still require policy controls during
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signaling of TE LSPs to enforce their bilateral or multilateral
agreements at AS boundaries, but signaling is out of scope for this
document.
4.5.1. Inter-AS PCE Peering Policy Controls
An inter-AS PCE sends path computation requests to its neighboring
inter-AS PCEs, and an inter-AS PCE that receives such a request
enforces policies applicable to the sender of the request. These
policies may include rewriting some of the parameters or rejecting
requests based on parameter values. Such policies may be applied for
PCEs belonging to different SPs or to PCEs responsible for ASes
within a single SP administrative domain. Parameters that might be
subject to policy include bandwidth, setup/holding priority, Fast
Reroute request, Differentiated Services Traffic Engineering (DS-TE)
Class Type (CT), and others as specified in section 5.2.2.1 of
[RFC4216].
For path computation requests that are not compliant with locally
configured policies, PCECP SHOULD enable a PCE to send an error
message to the requesting PCC or PCE indicating that the request has
been rejected because a specific parameter did not satisfy the local
policy.
4.5.2. Inter-AS PCE Re-Interpretation Policies
Each SP may have different definitions in its use of, for example,
DS-TE TE classes. An inter-AS PCE receiving a path computation
request needs to interpret the parameters and constraints and adapt
them to the local environment. Specifically, a request constructed
by a PCC or PCE in one AS may have parameters and constraints that
should be interpreted differently or translated by the receiving PCE
that is in a different AS. A list of signaling parameters subject to
policy re-interpretation at AS borders can be found in section
5.2.2.2 of [RFC4216], and the list for path computation request
parameters and constraints is the same. In addition, the transit SPs
along the inter-AS TE path may be GMPLS transport providers, which
may require re-interpretation of MPLS-specific PCECP path computation
request objects in order to enable path computation over a GMPLS
network or vice versa.
5. Security Considerations
The PCECP is a communications protocol for use between potentially
remote entities (PCCs and PCEs) over an IP network. Security
concerns arise in order to protect the PCC, PCE, and the information
they exchange. [RFC4758] specifies requirements on the PCECP to
protect against spoofing, snooping, and DoS attacks. That document
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is concerned with general protocol requirements applicable to the
basic use of the PCECP. This document is specific to the application
of the PCE architecture in an inter-AS environment, and so it is
appropriate to highlight the security considerations that apply in
that environment.
Security requirements that exist within a single administrative
domain become critical in the multi-AS case when the control of IP
traffic and access to the network may leave the authority of a single
administration.
5.1. Use and Distribution of Keys
How the participants in a PCECP session discover each other and the
need for the session is out of scope of this document. It may be
through configuration or automatic discovery. However, when a PCECP
session is established, the PCECP speakers MUST have mechanisms to
authenticate each other's identities and validate the data they
exchange. They also SHOULD have mechanisms to protect the data that
they exchange via encryption. Such mechanisms usually require the
use of keys, and so the PCECP MUST describe techniques for the
exchange and use of security keys. Where inter-AS PCE discovery is
used, and PCECP security is required, automated key distribution
mechanisms MUST also be used. Since such key exchange must
(necessarily) operate over an AS boundary, proper consideration needs
to be given to how inter-AS key exchanges may be carried out and how
the key exchange, itself, may be secured. Key distribution
mechanisms MUST be defined with consideration of [RFC4107]. Where a
PCECP session is configured between a pair of inter-AS PCEs, a
security key may be manually set for that session.
5.2. Application of Policy
Policy forms an important part of the operation of PCEs in an inter-
AS environment as described in Section 4.5, especially when ASes are
administrated by different SPs. A wider discussion of the
application of policy to the PCE architecture can be found in
[PCE-POLICY].
Policy may also form part of the security model for the PCECP and may
be particularly applicable to inter-AS path computation requests. A
fundamental element of the application of policy at a PCE is the
identity of the requesting PCC/PCE. This makes the use of
authentication described in Section 5.1 particularly important.
Where policy information is exchanged as part of the computation
request and/or response, the policy object is transparent to the
PCECP being delivered un-inspected and unmodified to the policy
component of a PCE or PCC. Therefore, the policy components are
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responsible for protecting (for example, encrypting) the policy
information and using additional identification and authentication if
a higher level of validation is required than is provided by the base
protocol elements of the PCECP.
5.3. Confidentiality
The PCECP MUST provide a mechanism to preserve the confidentiality of
path segments computed by a PCE in one AS and provided in a
computation response to another AS.
Furthermore, a PCE SHOULD be provided with a mechanism to mask its
identity such that its presence in the path computation chain in a
cooperative PCE model (such as described in [BRPC]) cannot be derived
from the computed path. This will help to protect the PCE from
targeted attacks. Clearly, such confidentiality does not extend to
the PCECP peer (i.e., a PCC or another PCE) that invokes the PCE with
a path computation request.
5.4. Falsification of Information
In the PCE architecture, when PCEs cooperate, one PCE may return a
path computation result that is composed of multiple path segments,
each computed by a different PCE. In the inter-AS case, each PCE may
belong to a different administrative domain, and the source PCC might
not know about the downstream PCEs, nor fully trust them. Although
it is possible and RECOMMENDED to establish a chain of trust between
PCEs, this might not always be possible. In this case, it becomes
necessary to guard against a PCE changing the information provided by
another downstream PCE. Some mechanism MUST be available in the
PCECP, and echoed in the corresponding signaling, that allows an AS
to verify that the signaled path conforms to the path segment
computed by the local PCE and returned on the path computation
request.
6. Acknowledgments
We would like to thank Adrian Farrel, Jean-Philippe Vasseur, and Jean
Louis Le Roux for their useful comments and suggestions. Pasi Eronen
and Sandy Murphy provided valuable early Security Directorate
reviews. Adrian Farrel re-wrote the Security Considerations section.
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7. Normative References
[RFC4107] Bellovin, S. and R. Housley, "Guidelines for
Cryptographic Key Management", BCP 107, RFC 4107, June
2005.
[RFC4216] Zhang, R., Ed., and J.-P. Vasseur, Ed., "MPLS Inter-
Autonomous System (AS) Traffic Engineering (TE)
Requirements", RFC 4216, November 2005.
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.
[RFC4657] Ash, J., Ed., and J. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, September 2006.
8. Informative References
[BRPC] Vasseur, JP., Zhang, R., Bitar, N., and JL. Le Roux, "A
Backward Recursive PCE-based Computation (BRPC)
Procedure To Compute Shortest Constrained Inter-domain
Traffic Engineering Label Switched paths", Work in
Progress, April 2008.
[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.
[RFC4758] Nystroem, M., "Cryptographic Token Key Initialization
Protocol (CT-KIP) Version 1.0 Revision 1", RFC 4758,
November 2006.
[RFC5150] Ayyangar, A., Kompella, K., Vasseur, JP., and A. Farrel,
"Label Switched Path Stitching with Generalized
Multiprotocol Label Switching Traffic Engineering (GMPLS
TE)", RFC 5150, February 2008.
[RFC5151] Farrel, A., Ed., Ayyangar, A., and JP. Vasseur, "Inter-
Domain MPLS and GMPLS Traffic Engineering -- Resource
Reservation Protocol-Traffic Engineering (RSVP-TE)
Extensions", RFC 5151, February 2008.
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[RFC5152] Vasseur, JP., Ed., Ayyangar, A., Ed., and R. Zhang, "A
Per-Domain Path Computation Method for Establishing
Inter-Domain Traffic Engineering (TE) Label Switched
Paths (LSPs)", RFC 5152, February 2008.
[PCE-POLICY] Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash,
"Policy-Enabled Path Computation Framework", Work in
Progress, October 2007.
Authors' Addresses
Nabil Bitar
Verizon
117 West Street
Waltham, MA 02451 USA
EMail: nabil.n.bitar@verizon.com
Kenji Kumaki
KDDI R&D Laboratories, Inc.
2-1-15 Ohara Fujimino
Saitama 356-8502, JAPAN
EMail: ke-kumaki@kddi.com
Raymond Zhang
BT
2160 E. Grand Ave.
El Segundo, CA 90245 USA
EMail: Raymond.zhang@bt.com
Bitar, et al. Informational [Page 14]
ERRATA
