PCE Working Group D. Dhody
Internet-Draft U. Palle
Intended status: Experimental Huawei Technologies India Pvt
Expires: January 6, 2013 Ltd
R. Casellas
CTTC - Centre Tecnologic de
Telecomunicacions de Catalunya
July 5, 2012
Standard Representation Of Domain Sequence
draft-ietf-pce-pcep-domain-sequence-01
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 has been
identified as a key requirement for P2P and P2MP scenarios. 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. This document
specifies a standard representation and encoding of a domain
sequence, which is defined as an ordered sequence of domains
traversed to reach the destination domain. This document also
defines new sub-objects to be used to encode domain identifiers.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 6, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Detail Description . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Domains . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Domain-Sequence . . . . . . . . . . . . . . . . . . . . . 6
3.3. Standard Representation . . . . . . . . . . . . . . . . . 7
3.3.1. New Sub-Objects . . . . . . . . . . . . . . . . . . . 7
3.3.1.1. Autonomous system . . . . . . . . . . . . . . . . 7
3.3.1.2. IGP Area . . . . . . . . . . . . . . . . . . . . . 8
3.3.2. Use in PCEP Objects . . . . . . . . . . . . . . . . . 9
3.3.2.1. Include Route Object . . . . . . . . . . . . . . . 9
3.3.2.2. Exclude Route Object . . . . . . . . . . . . . . . 13
3.3.2.3. Explicit Route Object . . . . . . . . . . . . . . 15
3.3.2.4. Explicit Exclusion Route Sub-Object . . . . . . . 16
3.4. Other Considerations . . . . . . . . . . . . . . . . . . . 16
3.4.1. Inter-Area Path Computation . . . . . . . . . . . . . 16
3.4.2. Inter-AS Path Computation . . . . . . . . . . . . . . 18
3.4.2.1. Example 1 . . . . . . . . . . . . . . . . . . . . 18
3.4.2.2. Example 2 . . . . . . . . . . . . . . . . . . . . 20
3.4.3. Boundary Node and Inter-AS-Link . . . . . . . . . . . 22
3.4.4. PCE serving multiple domains . . . . . . . . . . . . . 23
3.4.5. P2MP . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.4.6. HPCE . . . . . . . . . . . . . . . . . . . . . . . . . 23
3.4.7. Relationship to PCE Sequence . . . . . . . . . . . . . 25
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
4.1. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . . 25
4.2. New Sub-Objects . . . . . . . . . . . . . . . . . . . . . 26
4.3. Error Object Field Values . . . . . . . . . . . . . . . . 26
5. Security Considerations . . . . . . . . . . . . . . . . . . . 26
6. Manageability Considerations . . . . . . . . . . . . . . . . . 27
6.1. Control of Function and Policy . . . . . . . . . . . . . . 27
6.2. Information and Data Models . . . . . . . . . . . . . . . 27
6.3. Liveness Detection and Monitoring . . . . . . . . . . . . 27
6.4. Verify Correct Operations . . . . . . . . . . . . . . . . 27
6.5. Requirements On Other Protocols . . . . . . . . . . . . . 27
6.6. Impact On Network Operations . . . . . . . . . . . . . . . 28
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 28
8.1. Normative References . . . . . . . . . . . . . . . . . . . 28
8.2. Informative References . . . . . . . . . . . . . . . . . . 28
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1. Introduction
A PCE may be used to compute end-to-end paths across multi-domain
environments using a per-domain path computation technique [RFC5152].
The so called backward recursive path computation (BRPC) mechanism
[RFC5441] defines a PCE-based path computation procedure to compute
inter-domain constrained (G)MPLS TE LSPs. However, both per-domain
and BRPC techniques assume that the sequence of domains to be crossed
from source to destination is known, either fixed by the network
operator or obtained by other means. For inter-domain point-to-
multi-point (P2MP) tree, [PCE-P2MP-PROCEDURES] assumes the domain-
tree is known.
The list of domains in a point-to-point (P2P) path or a point-to-
multi-point (P2MP) tree is usually a constraint in the path
computation request. The PCE decouples the domain to determine the
next PCE to forward the request.
According to BRPC mechanism the PCC MAY indicate the sequence of
domains to be traversed using the Include Route Object (IRO) defined
in [RFC5440].
This document proposes a standard way to represent and encode a
domain sequence using IRO in various deployment scenarios including
P2P, P2MP and Hierarchical PCE (HPCE) [PCE-HIERARCHY-FWK].
The domain sequence (the set of domains traversed to reach the
destination domain) is either administratively predetermined or
discovered by some means (H-PCE) that is outside of the scope of this
document. Here the focus is only on a standard representation of the
domain sequence in all possible scenarios.
1.1. 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 [RFC2119].
2. Terminology
The following terminology is used in this document.
ABR: OSPF Area Border Router. Routers used to connect two IGP
areas.
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AS: Autonomous System.
ASBR: Autonomous System Boundary Router.
BN: Boundary Node, Can be an ABR or ASBR.
BRPC: Backward Recursive Path Computation
Domain: Any collection of network elements within a common sphere of
address management or path computational responsibility. Examples
of domains include Interior Gateway Protocol (IGP) areas and
Autonomous Systems (ASs).
Domain-Seq: An ordered sequence of domains traversed to reach the
destination domain.
ERO: Explicit Route Object
H-PCE: Hierarchical PCE
IGP: Interior Gateway Protocol. Either of the two routing
protocols, Open Shortest Path First (OSPF) or Intermediate System
to Intermediate System (IS-IS).
IRO: Include Route Object
IS-IS: Intermediate System to Intermediate System.
OSPF: Open Shortest Path First.
PCC: Path Computation Client: any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element. An entity (component, application,
or network node) that is capable of computing a network path or
route based on a network graph and applying computational
constraints.
P2MP: Point-to-Multipoint
P2P: Point-to-Point
RSVP: Resource Reservation Protocol
TE LSP: Traffic Engineering Label Switched Path.
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3. Detail Description
3.1. Domains
A domain can be defined as a separate administrative or geographic
environment within the network. A domain may be further defined as a
zone of routing or computational ability. Under these definitions a
domain might be categorized as an Autonomous System (AS) or an
Interior Gateway Protocol (IGP) area ( as per [RFC4726] and
[RFC4655]). To uniquely identify a domain in the domain sequence
both AS and Area-id MAYBE important.
3.2. Domain-Sequence
A domain-sequence is an ordered sequence of domains traversed to
reach the destination domain. In this context a Domain could be an
Autonomous System (AS) or an IGP Area. Note that an AS can be
further made of multiple Areas.
Domain Sequence can be applied as a constraint and carried in path
computation request to PCE(s). In case of HPCE [PCE-HIERARCHY-FWK]
Parent PCE MAY send the domain sequence as a result in path
computation reply.
In this context, ordered sequence is important, in a P2P path, the
domains listed appear in the order that they are crossed. In a P2MP
path, the domain tree is represented as list of domain sequences.
One main goal of the Domain-Sequence is to enable a PCE to select the
next PCE to forward the path computation request based on the domain
information.
A PCC or PCE MAY add an additional constraints covering which
Boundary Nodes (ABR or ASBR) or Border links (Inter-AS-link) MUST be
traversed while defining a domain sequence.
Thus a Domain-Sequence MAY be made up of one or more of -
o AS Number
o Area ID
o Boundary Node ID
o Inter-AS-Link Address
Consequently, a Domain-Sequence can be used:
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1. by a PCE in order to discover or select the next PCE in a
collaborative path computation, such as in BRPC [RFC5441];
2. by the Parent PCE to return the domain sequence when unknown,
this can further be an input to BRPC procedure;
3. By a PCC (or PCE) to constraint the domains used in a H-PCE path
computation, explicitly specifying which domains to be expanded;
3.3. Standard Representation
3.3.1. New Sub-Objects
Some sub-objects are defined in [RFC3209], [RFC3473], [RFC3477] and
[RFC4874], but new sub-objects related to Domain-Sequence are needed.
3.3.1.1. Autonomous system
[RFC3209] already defines 2 octet AS number.
To support 4 octet AS number as per [RFC4893] following subobject is
defined:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AS Id (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L: The L bit is an attribute of the subobject as define in [RFC3209].
Type: (TBA by IANA) indicating 4 octet AS Number.
Length: 8 (Total length of the subobject in bytes).
Reserved: Zero at transmission, Ignored at receipt.
AS-ID: The 4 octet AS Number. Note that if 16-bit AS numbers are in
use, the low order bits (16 through 31) should be used and the high
order bits (0 through 15) should be set to zero.
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3.3.1.2. IGP Area
Since the length and format of Area-id is different for OSPF and
ISIS, following two subobjects are defined:
For OSPF, the area-id is a 32 bit number. The Subobject looks
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OSPF Area Id (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L: The L bit is an attribute of the subobject as define in [RFC3209].
Type: (TBA by IANA) indicating 4 octet OSPF Area ID.
Length: 8 (Total length of the subobject in bytes).
Reserved: Zero at transmission, Ignored at receipt.
OSPF Area Id: The 4 octet OSPF Area ID.
For IS-IS, the area-id is of variable length and thus the length of
the Subobject is variable. The Area-id is as described in IS-IS by
ISO standard [ISO 10589].
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | Area-Len | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// IS-IS Area ID //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L: The L bit is an attribute of the subobject as define in [RFC3209].
Type: (TBA by IANA) indicating IS-IS Area ID.
Length: Variable (Total length of the subobject in bytes including
padding). The Length MUST be at least 4, and MUST be a multiple of
4.
Area-Len: Variable (Length of the actual (non-padded) IS-IS Area
Identifier in octets; Valid values are from 2 to 11 inclusive).
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Reserved: Zero at transmission, Ignored at receipt.
IS-IS Area Id: The variable-length IS-IS area identifier. Padded
with trailing zeroes to a four-octet boundary.
3.3.2. Use in PCEP Objects
These sub-objects MAYBE used in -
o Include Route Object (IRO): As per [RFC5440], used to specify set
of network elements that MUST be traversed. These subobjects are
used to specify the domain-sequence that MUST be traversed to
reach the destination.
o Exclude Route Object (XRO): As per [RFC5521], used to specify
certain abstract nodes that MUST be excluded from whole path.
These subobjects are used to specify certain domains that MUST be
avoided to reach the destination.
o Explicit Route Object (ERO): As per [RFC5440],used to specify a
computed path in the network. These subobjects are used to
specify the domain-sequence when computed by a Parent PCE
([PCE-HIERARCHY-FWK]).
o Explicit Exclusion Route Sub-Object (EXRS): As per [RFC5521], used
to specify exclusion of certain abstract nodes between a specific
pair of nodes. EXRS are a sub-object inside the IRO. These
subobjects are used to specify the domains that must be excluded
between two abstract nodes.
3.3.2.1. Include Route Object
3.3.2.1.1. Option 1: New IRO Object Type
The IRO (Include Route Object) [RFC5440] is an optional object used
to specify a set of specified network elements that the computed path
MUST traverse. [RFC5440] in its description of IRO does not
constrain the sub-objects to be in a given particular order. When
considering a domain sequence, the domain relative ordering is a
basic criterion and, as such, this document specifies a new IRO
object type.
We define a new type of IRO Object to define Domain Sequence.
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IRO Object-Class is 10.
IRO Object-Type is TBD. (2 suggested value to IANA)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// (Subobjects) //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sub-objects: The IRO is made of sub-objects identical to the ones
defined in [RFC3209], [RFC3473], and [RFC3477], where the IRO sub-
object type is identical to the sub-object type defined in the
related documents. Some new sub-objects related to Domain-Sequence
are also added in this document.
The following sub-object types are used.
Type Sub-object
1 IPv4 prefix
2 IPv6 prefix
4 Unnumbered Interface ID
32 Autonomous system number (2 Byte)
33 Explicit Exclusion (EXRS)
TBD Autonomous system number (4 Byte)
TBD OSPF Area id
TBD ISIS Area id
[RFC3209] defines sub-objects for IPv4, IPv6 and unnumbered Interface
ID, which in the context of domain-sequence is used to specify
Boundary Node (ABR/ASBR) and Inter-AS-Links. The sub-objects for AS
Number (2 or 4 Byte) and IGP Area is used to specify the domains in
the domain-sequence.
The new IRO Object-Type used to define the domain-sequence would
handle the L bit (Loose / Strict) in the sub-objects.
Note that PCReq message is free to carry both type of IRO with IRO
Type 1 ([RFC5440]) used to specify the intra-domain abstract nodes
and resources and the new IRO Type as described in this document to
specify the domain-sequence.
All other rules of PCEP objects and message processing (ex. P bit
handling of Common Object Header) is as per [RFC5440].
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3.3.2.1.1.1. Mode of Operation
A domain sequence IRO object constraints or defines the domains
involved in a multi-domain path computation, typically involving two
or more collaborative PCEs.
A domain sequence can have varying degrees on granularity; it is
possible to have a domain sequence composed of, uniquely, AS
identifiers. It is also possible to list the involved areas for a
given AS.
In any case, the mapping between domains and responsible PCEs is not
defined in this document. It is assumed that a PCE that needs to
obtain a "next PCE" from a domain sequence is able to do so (e.g. via
administrative configuration, or discovery).
A PCC builds a domain sequence IRO (new type) to encode the domain
sequence, that is all domains that it wishes the cooperating PCEs to
traverse in order to compute the end to end path.
For each inclusion, the PCC clears the L-bit to indicate that the PCE
is required to include the domain, or sets the L-bit to indicate that
the PCC simply desires that the domain be included in the domain-
sequence.
When a PCE receives a PCReq message it looks for a domain sequence
IRO (new type) to see if domain-sequence are required. If the PCE
finds more than one domain sequence IRO (new type), it MUST use the
first one in the message and MUST ignore subsequent instances.
If the PCE does not recognize the domain sequence IRO (new type), it
MUST return a PCErr message with Error-Type "Unknown Object" and
Error-value "Unrecognized object Type" as described in [RFC5440].
If the PCE is unwilling or unable to process the domain sequence IRO
(new type), it MUST return a PCErr message with the Error-Type "Not
supported object" and follow the relevant procedures described in
[RFC5440].
If a PCE that supports the domain sequence IRO (new type) and
encounters a subobject that it does not support or recognize, it MUST
act according to the setting of the L-bit in the subobject. If the
L-bit is clear, the PCE MUST respond with a PCErr with Error-Type
"Unrecognized subobject" and set the Error-Value to the subobject
type code. If the L-bit is set, the PCE MAY respond with a PCErr as
already stated or MAY ignore the subobject: this choice is a local
policy decision.
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If a PCE parses a domain sequence IRO (new type) and encounters these
subobject that it recognizes, it MUST act according to the
requirements expressed in the subobject. That is, if the L-bit is
clear, the PCE(s) MUST produce a path that follows domain-sequence
nodes in order identified by the sub-objects in the path. If the
L-bit is set, the PCE(s) SHOULD produce a path along the domain
sequence unless it is not possible to construct a path complying with
the other constraints expressed in the PCReq message.
A successful path computation reported in a PCRep message MUST
include an ERO to specify the path that has been computed as
specified in [RFC5440] following the domain-sequence.
When a PCE returns a path in a PCRep, it MAY also supply a domain
sequence IRO (new type) in a PCRep message with the NO-PATH object
indicates that the set of elements of the original domain sequence
IRO prevented the PCE from finding a path.
Sub-Object types for AS and IGP Area guide the next domain selection
and finding the PCE serving that domain.
Note that a particular domain in the domain-sequence can be
identified by -
o Just Area: Only the IGP (OSPF or ISIS) Area subobject is used to
identify the next domain. (Refer Figure 1)
o Just AS: Only the AS subobject is used to identify the next
domain. (Refer Figure 2)
o AS and IGP Area: Combination of both AS and Area are used to
identify the next domain. In this case the order is AS Subobject
followed by Area. (Refer Figure 3)
Sub-Object of other types representing Boundary Node or Inter-As-Link
do not pay any role in selection of next domain and subsequently PCE
selection in the domain-sequence. But they MUST be applied during
the final path computation procedure as before.
3.3.2.1.2. Option 2: Same IRO Object Type
The IRO (Include Route Object) [RFC5440] is an optional object used
to specify a set of specified network elements that the computed path
MUST traverse.
The new sub-objects denoting the domain-sequence is carried in the
same IRO Type 1, and all the rules of processing as specified in
[RFC5440] are applied.
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Note the following differences -
o Order: Since there is no inherent order specified in the encoding
of the subobjects in IRO Type 1 [RFC5440]. It is the job of PCE
to figure out the order of the domains to be crossed to reach the
destination domain. Note that in case of doubt, or when
applicable, PCE can still apply the ordering as specified in the
PCReq message.
o Loose / Strict: [RFC5440] state that the L bit of the sub-objects
within an IRO Type 1 [RFC5440] has no meaning. This is applicable
for sub-objects denoting domain-sequence as well.
o Scope: Sub-objects referring to domains and boundary nodes will
mix with subobjects for internal network nodes of multiple
domains. It is the job of PCE to figure out the scope and apply
the processing rules accordingly. The PCE should distinguish
between - the subobject is unknown (not in TED) or known but the
computation fails. The PCE processing the IRO MAY include as many
of the elements of the IRO as possible. If the PCE is passing the
request onwards, it is OK for it to have unknown nodes, and it can
assume that the next PCE might be able to satisfy the remaining
elements of the IRO. On the other hand, if the PCE is making an
end-to-end (or edge-to-edge, or end-to-edge) path and will return
the response to a PCC (rather than pass it on) then the PCE must
fail if it cannot satisfy the IRO. Ultimately, when the path
segments are aggregated by a head-end PCE or by a parent PCE, that
PCE can check to see whether any elements of the IRO are still
missing and handle accordiangly.
3.3.2.2. Exclude Route Object
The Exclude Route Object (XRO) [RFC5521] is an optional object used
to specify exclusion of certain abstract nodes or resources from the
whole path.
The following subobject types are defined to be used in XRO as
defined in [RFC3209], [RFC3477], [RFC4874], and [RFC5521].
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Type Sub-object
1 IPv4 prefix
2 IPv6 prefix
4 Unnumbered Interface ID
32 Autonomous system number (2 Byte)
34 SRLG
64 IPv4 Path Key
65 IPv6 Path Key
TBD Autonomous system number (4 Byte)
TBD OSPF Area id
TBD ISIS Area id
The new subobjects to support 4 octet AS and IGP (OSPF / ISIS) Area
MAY also be used in the XRO to specify exclusion of certain domains
in the path computation procedure.
The X-bit indicates whether the exclusion is mandatory or desired. 0
indicates that the domain specified MUST be excluded from the path
computed by the PCE(s). 1 indicates that the domain specified SHOULD
be excluded from the inter-domain path computed by the PCE(s), but
MAY be included subject to PCE policy and the absence of a viable
path that meets the other constraints and excludes the domain. All
other fields are consistent with the definition in Section 3.3.1.
4 Octet Autonomous system:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AS Id (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
OSPF Area:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OSPF Area Id (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IS-IS Area:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X| Type | Length | Area-Len | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// IS-IS Area ID //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
If a PCE that supports XRO and encounters a subobject that it does
not support or recognize, it MUST act according to the setting of the
X-bit in the subobject. If the X-bit is clear, the PCE MUST respond
with a PCErr with Error-Type "Unrecognized subobject" and set the
Error-Value to the subobject type code. If the X-bit is set, the PCE
MAY respond with a PCErr as already stated or MAY ignore the
subobject: this choice is a local policy decision.
All the other processing rules are as per [RFC5521].
3.3.2.3. Explicit Route Object
The Explicit Route Object (ERO) [RFC5440] is used to specify a
computed path in the network. PCEP ERO sub-object types correspond
to RSVP-TE ERO sub-object types as defined in [RFC3209], [RFC3473],
[RFC3477], [RFC4873], [RFC4874], and [RFC5520].
Type Sub-object
1 IPv4 prefix
2 IPv6 prefix
3 Label
4 Unnumbered Interface ID
32 Autonomous system number (2 Byte)
33 Explicit Exclusion (EXRS)
37 Protection
64 IPv4 Path Key
65 IPv6 Path Key
TBD Autonomous system number (4 Byte)
TBD OSPF Area id
TBD ISIS Area id
The new subobjects to support 4 octet AS and IGP (OSPF / ISIS) Area
MAY also be used in the ERO to specify an abstract node (a group of
nodes whose internal topology is opaque to the ingress node of the
LSP). Using this concept of abstraction, an explicitly routed LSP
can be specified as a sequence of domains.
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In case of Hierarchical PCE, a Parent PCE ([PCE-HIERARCHY-FWK]) MAY
be requested to find the domain-sequence. The Parent PCE MUST use
ERO with AS and IGP Area subobjects to encode the computed domain-
sequence. Refer example in Section 3.4.6.
3.3.2.4. Explicit Exclusion Route Sub-Object
Explicit Exclusion Route Sub-Object (EXRS) [RFC5521] is used to
specify exclusion of certain abstract nodes between a specific pair
of nodes.
The EXRS subobject may carry any of the subobjects defined for
inclusion in the XRO, thus the new subobjects to support 4 octet AS
and IGP (OSPF / ISIS) Area MAY also be used in the EXRS. The
meanings of the fields of the new XRO subobjects are unchanged when
the subobjects are included in an EXRS, except that scope of the
exclusion is limited to the single hop between the previous and
subsequent elements in the IRO.
All the processing rules are as per [RFC5521].
3.4. Other Considerations
3.4.1. Inter-Area Path Computation
In an inter-area path computation where ingress and egress belong to
different IGP area, the domain sequence MAYBE represented using a
ordered list of AREA sub-objects. AS number MAYBE skipped, as area
information is enough to select the next PCE.
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+-------------------+ +-------------------+
| | | |
| +--+ | | +--+ |
| +--+ | | | | | | |
| | | +--+ | | +--+ +--+ |
| +--* + + | | |
| | | +--+ |
| *--+ + + |
| | | | | +--+ |
| +--+ | | | | |
| |+--------------------------+| +--+ |
| ++++ +-++ |
| |||| +--+ | || |
| Area 2 ++++ | | +-++ Area 4 |
+-------------------+| +--+ |+-------------------+
| |
| +--+ |
| +--+ | | |
| | | +--+ |
| +--+ |
| |
| |
| |
| |
| +--+ |
| | | |
| +--+ |
+------------------+| |+--------------------+
| ++-+ +-++ |
| || | | || |
| ++-+ Area 0 +-++ |
| |+--------------------------+| +--+ |
| +--+ | | | | |
| | | | | +--+ |
| +--+ +--+ | | |
| | | + + +--+ |
| +--+ | | | | |
| + + +--+ |
| +--+ | | |
| | | | | +--+ |
| +--+ | | | | |
| | | +--+ |
| | | |
| Area 1 | | Area 5 |
+------------------+ +--------------------+
AS Number is 100.
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Figure 1: Inter-Area Path Computation
This could be represented as <IRO> as:
+---------+ +---------+ +---------+ +---------+
|IRO | |Sub | |Sub | |Sub |
|Object | |Object | |Object | |Object |
|Header | |Area 2 | |Area 0 | |Area 4 |
| | | | | | | |
| | | | | | | |
+---------+ +---------+ +---------+ +---------+
+---------+ +---------+ +---------+ +---------+ +---------+
|IRO | |Sub | |Sub | |Sub | |Sub |
|Object | |Object As| |Object | |Object | |Object |
|Header | |100 | |Area 2 | |Area 0 | |Area 4 |
| | | | | | | | | |
| | | | | | | | | |
+---------+ +---------+ +---------+ +---------+ +---------+
AS is optional and it MAY be skipped. PCE should be able to
understand both notations.
3.4.2. Inter-AS Path Computation
In inter-AS path computation, where ingress and egress belong to
different AS, the domain sequence is represented using an ordered
list of AS sub-objects. The domain sequence MAY further include
decomposed area information in AREA sub-objects.
3.4.2.1. Example 1
As shown in Figure 2, where AS to be made of a single area, the area
subobject MAY be skipped in the domain sequence as AS is enough to
uniquely identify the next domain and PCE.
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+---------------------------------+
|AS 200 |
| +------+ |
| | | |
+------------------------+ | | | +------+ |
| AS 100 | | +------+ | | |
| +------+ | | +------+ | | |
| | +-+-----+-+ | +------+ |
| | | | | | | |
| +------+ | | +------+ |
| +------+ | | +------+ |
| | | | | | | |
| | | | | | | |
| +------+ | | +------+ |
| | | |
| +------+ | | +------+ |
| | +-+-----+-+ | +------+ |
| | | | | | | | | |
| +------+ | | +------+ | | |
| | | +------+ |
| | | |
| | | |
| +------+ | | +------+ |
| | | | | | | |
| |PCE | | | |PCE | |
| +------+ | | +------+ |
| | | |
+------------------------+ | |
+---------------------------------+
Both AS are made of Area 0.
Figure 2: Inter-AS Path Computation
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This could be represented as <IRO> as:
+---------+ +---------+ +---------+
|IRO | |Sub | |Sub |
|Object | |Object As| |Object As|
|Header | |100 | |200 |
| | | | | |
| | | | | |
+---------+ +---------+ +---------+
+---------+ +---------+ +---------+ +---------+ +---------+
|IRO | |Sub | |Sub | |Sub | |Sub |
|Object | |Object As| |Object | |Object As| |Object |
|Header | |100 | |Area 0 | |200 | |Area 0 |
| | | | | | | | | |
| | | | | | | | | |
+---------+ +---------+ +---------+ +---------+ +---------+
Area is optional and it MAY be skipped. PCE should be able to
understand both notations.
3.4.2.2. Example 2
As shown in Figure 3, where AS 200 is made up of multiple areas and
multiple domain-sequence exist, PCE MAY include both AS and AREA
subobject to uniquely identify the next domain and PCE.
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|
| +-------------+ +----------------+
| |Area 2 | |Area 4 |
| | +--+| | +--+ |
| | | || | | | |
| | +--+ +--+| | +--+ +--+ |
| | | | | | | | |
| | *--+ | | +--+ |
| | / +--+ | | +--+ |
| |/ | | | | | | |
| / +--+ | | +--+ +--+ |
| /| +--+ |+--------------+| | | |
|/ | | | ++-+ +-++ +--+ |
+-------------+/ | +--+ || | | || |
| /| | ++-+ +-++ |
| +--*|| +-------------+| |+----------------+
| | ||| | +--+ |
| +--+|| | | | |
| +--+ || | +--+ |
| | | || | |
| +--+ || | |
| || | +--+ |
|+--+ || | | | |
|| | || | +--+ |
|+--+ || | |
| || | +--+ |
| +--+ || +------------+ | | | |+----------------+
| | | || |Area 3 +-++ +--+ +-++ Area 5 |
| +--+ || | | || | || |
| || | +-++ +-++ |
| +--+|| | +--+ | | Area 0 || +--+ |
| | ||| | | | | +--------------+| | | |
| +--*|| | +--+ | | +--+ |
| \| | | | +--+ |
|Area 1 |\ | +--+ | | +--+ | | |
+-------------+|\ | | | | | | | +--+ |
| \| +--+ +--+ | +--+ |
| \ | | | |
| |\ +--+ | +--+ |
| | \ +--+ | | | | |
| | \| | | | +--+ |
| | *--+ | | |
| | | | |
| +------------+ +----------------+
|
|
As 100 | AS 200
|
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Figure 3: Inter-AS Path Computation
The domain sequence can be carried in IRO as shown below:
+-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
|IRO | |Sub | |Sub | |Sub | |Sub | |Sub | |Sub |
|Object | |Object | |Object | |Object | |Object | |Object | |Object |
|Header | |As 100 | |Area 1 | |AS 200 | |Area 3 | |Area 0 | |Area 4 |
| | | | | | | | | | | | | |
+-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
Combination of both AS and Area uniquely identify a domain in the domain
sequence.
Note that an Area domain identifier always belongs to the previous AS
that appear before it or, if no AS sub-objects are present, it is
assumed to be the current AS.
If the area information cannot be provided, PCE MAY forward the path
computation request to the next PCE based on AS only. If multiple
PCEs of different area domain exist, PCE MAY apply local policy to
select the next PCE. Furthermore the domain sequence (list of areas
within AS) in the next PCE MAYBE pre-administered or MAYBE discovered
via some mechanism (ex. HPCE).
3.4.3. Boundary Node and Inter-AS-Link
A PCC or PCE MAY add additional constraints covering which Boundary
Nodes (ABR or ASBR) or Border links (Inter-AS-link) MUST be traversed
while defining a domain sequence. In which case the Boundary Node or
Link MAY be encoded as a part of the domain-sequence using the
existing sub-objects.
Boundary Node (ABR / ASBR) can be encoded using the IPv4 or IPv6
prefix sub-objects. The Inter-AS link can be encoded using the IPv4
or IPv6 prefix or unnumbered interface sub-objects.
For Figure 1, an ABR to be traversed can be specified as:
+---------+ +---------+ +---------++---------+ +---------+
|IRO | |Sub | |Sub ||Sub | |Sub |
|Object | |Object | |Object ||Object | |Object |
|Header | |Area 2 | |IPv4 ||Area 0 | |Area 4 |
| | | | |x.x.x.x || | | |
| | | | | || | | |
+---------+ +---------+ +---------++---------+ +---------+
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For Figure 2, an inter-AS-link to be traversed can be specified as:
+---------+ +---------+ +---------+ +---------+ +---------+
|IRO | |Sub | |Sub | |Sub | |Sub |
|Object | |Object As| |Object | |Object | |Object As|
|Header | |100 | |IPv4 | |IPv4 | |200 |
| | | | |x.x.x.x | |x.x.x.x | | |
| | | | | | | | | |
+---------+ +---------+ +---------+ +---------+ +---------+
3.4.4. PCE serving multiple domains
A single PCE MAYBE responsible for multiple domains; for example PCE
function deployed on an ABR. Domain sequence should have no impact
on this. PCE which can support 2 adjacent domains can internally
handle this situation without any impact on the neighboring domains.
3.4.5. P2MP
In case of inter-domain P2MP path computation, (Refer
[PCE-P2MP-PROCEDURES]) the path domain tree is nothing but a series
of Domain Sequences, as shown in the below figure:
D1-D3-D6, D1-D3-D5 and D1-D2-D4.
D1
/ \
D2 D3
/ / \
D4 D5 D6
All rules of processing as applied to P2P can be applied to P2MP as
well.
In case of P2MP, different destinations MAY have different domain
sequence within the domain tree, it requires domain-sequence to be
attached per destination. (Refer [PCE-P2MP-PER-DEST])
3.4.6. HPCE
As per [PCE-HIERARCHY-FWK], consider a case as shown in Figure 4
consisting of multiple child PCEs and a parent PCE.
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+--------+
| Parent |
| PCE |
+--------+
+-------------------+ +-------------------+
| +--+ | | +--+ |
| +--+ | | | | | | |
| | | +--+ | | +--+ +--+ |
| +--* + + | | |
| | | +--+ |
| *--+ + + |
| | | | | +--+ |
| +--+ | | | | |
| |+--------------------------+| +--+ |
| ++++ +-++ |
| |||| +--+ | || |
| Area 2 ++++ | | +-++ Area 4 |
+-------------------+| +--+ |+-------------------+
| +--+ |
| +--+ | | |
| | | +--+ |
| +--+ |
| |
| +--+ |
| | | |
| +--+ |
+------------------+| |+--------------------+
| ++-+ +-++ |
| || | | || |
| ++-+ Area 0 +-++ |
| |+--------------------------+| +--+ |
| +--+ | | | | |
| | | | | +--+ |
| +--+ +--+ | | |
| | | + + +--+ |
| +--+ | | | | |
| + + +--+ |
| +--+ | | |
| | | | | +--+ |
| +--+ | | | | |
| | | +--+ |
| Area 1 | | Area 5 |
+------------------+ +--------------------+
Figure 4: Hierarchical PCE
In HPCE implementation the initiator PCE - PCE(1) can request the
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parent PCE to determine the domain sequence and return in the path
computation reply message (PCRep), using the ERO Object. The ERO can
contain an ordered sequence of sub-object such as AS and Area (OSPF/
ISIS). In this case, the PCRep would carry the domain sequence
result as:
+---------+ +---------+ +---------+ +---------+
|ERO | |Sub | |Sub | |Sub |
|Object | |Object | |Object | |Object |
|Header | |Area 2 | |Area 0 | |Area 4 |
| | | | | | | |
| | | | | | | |
+---------+ +---------+ +---------+ +---------+
+---------+ +---------+ +---------+ +---------+ +---------+
|ERO | |Sub | |Sub | |Sub | |Sub |
|Object | |Object As| |Object | |Object | |Object |
|Header | |100 | |Area 2 | |Area 0 | |Area 4 |
| | | | | | | | | |
| | | | | | | | | |
+---------+ +---------+ +---------+ +---------+ +---------+
Note that, in the case of ERO objects, no new PCEP object type is
required since the ordering constraint is assumed.
3.4.7. Relationship to PCE Sequence
[RFC5886] and [PCE-P2MP-PROCEDURES] along with Domain Sequence
introduces the concept of PCE-Sequence, where a sequence of PCEs,
based on the domain sequence, should be decided and attached in the
PCReq at the very beginning of path computation.
An alternative would be to use domain sequences, note that PCE-
Sequence can be used along with domain-sequence in which case PCE-
Sequence SHOULD have higher precedence in selecting the next PCE in
the inter-domain path computation procedures. Note that Domain-
Sequence IRO constraints should still be checked as per the rules of
processing IRO.
4. IANA Considerations
4.1. PCEP Objects
The "PCEP Parameters" registry contains a subregistry "PCEP Objects".
IANA is requested to make the following allocations from this
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registry.
Object Name Reference
Class
10 IRO [RFC5440]
Object-Type
(TBA): Domain Sequence [This I.D.]
4.2. New Sub-Objects
The "PCEP Parameters" registry contains a subregistry "PCEP Objects"
with an entry for the Include Route Object (IRO) and Exclude Route
Object (XRO). IANA is requested to add further subobjects as
follows:
Subobject Type Reference
TBA 4 octet AS number [This I.D.]
TBA OSPF Area ID [This I.D.]
TBA IS-IS Area ID [This I.D.]
4.3. Error Object Field Values
The "PCEP Parameters" registry contains a subregistry "Error Types
and Values". IANA is requested to make the following allocations
from this subregistry
ERROR Meaning Reference
Type
TBA "Unrecognized subobject" [This I.D.]
Error-Value: type code
5. Security Considerations
This document specifies a standard representation of domain sequence,
which MAYBE used in inter-domain PCE scenarios as explained in other
RFC and drafts. The new sub-objects and domain sequence mechanisms
defined in this document allow finer and more specific control of the
path computed by a cooperating PCE(s). Such control increases the
risk if a PCEP message is intercepted, modified, or spoofed because
it allows the attacker to exert control over the path that the PCE
will compute or to make the path computation impossible. Therefore,
the security techniques described in [RFC5440] are considered more
important.
Note, however, that the domain sequence mechanisms also provide the
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operator with the ability to route around vulnerable parts of the
network and may be used to increase overall network security.
6. Manageability Considerations
6.1. Control of Function and Policy
Several local policy decisions should be made at the PCE. Firstly,
the exact behavior with regard to desired inclusion and exclusion of
domains must be available for examination by an operator and may be
configurable. Second, the behavior on receipt of an unrecognized
sub-objects with the L or X-bit set should be configurable and must
be available for inspection. The inspection and control of these
local policy choices may be part of the PCEP MIB module.
6.2. Information and Data Models
A MIB module for management of the PCEP is being specified in a
separate document [PCEP-MIB]. That MIB module allows examination of
individual PCEP messages, in particular requests, responses and
errors. The MIB module MUST be extended to include the ability to
view the domain-sequence extensions defined in this document.
6.3. Liveness Detection and Monitoring
Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in [RFC5440].
6.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC5440].
6.5. Requirements On Other Protocols
The Sub-objects defined in this document SHOULD be supported by RSVP
especially for per-domain path computation [RFC5152] where the
domains need to encoded in the RSVP messages.
Apart from this, mechanisms defined in this document do not imply any
requirements on other protocols in addition to those already listed
in [RFC5440].
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6.6. Impact On Network Operations
Mechanisms defined in this document do not have any impact on network
operations in addition to those already listed in [RFC5440].
7. Acknowledgments
We would like to thank Adrian Farrel, Pradeep Shastry, Suresh Babu,
Quintin Zhao, Fatai Zhang, Daniel King, Oscar Gonzalez, Chen Huaimo,
Venugopal Reddy, Reeja Paul and Sandeep Boina for their useful
comments and suggestions.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14,
RFC 2119, March 1997.
[ISO 10589] ISO, "Intermediate system to Intermediate
system routeing information exchange protocol
for use in conjunction with the Protocol for
providing the Connectionless-mode Network
Service (ISO 8473)", ISO/IEC 10589:2002.
8.2. Informative References
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T.,
Srinivasan, V., and G. Swallow, "RSVP-TE:
Extensions to RSVP for LSP Tunnels", RFC 3209,
December 2001.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource
ReserVation Protocol-Traffic Engineering
(RSVP-TE) Extensions", RFC 3473, January 2003.
[RFC3477] Kompella, K. and Y. Rekhter, "Signalling
Unnumbered Links in Resource ReSerVation
Protocol - Traffic Engineering (RSVP-TE)",
RFC 3477, January 2003.
[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
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Framework for Inter-Domain Multiprotocol Label
Switching Traffic Engineering", RFC 4726,
November 2006.
[RFC4873] Berger, L., Bryskin, I., Papadimitriou, D.,
and A. Farrel, "GMPLS Segment Recovery",
RFC 4873, May 2007.
[RFC4874] Lee, CY., Farrel, A., and S. De Cnodder,
"Exclude Routes - Extension to Resource
ReserVation Protocol-Traffic Engineering
(RSVP-TE)", RFC 4874, April 2007.
[RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-
octet AS Number Space", RFC 4893, May 2007.
[RFC5152] Vasseur, JP., Ayyangar, A., and R. Zhang, "A
Per-Domain Path Computation Method for
Establishing Inter-Domain Traffic Engineering
(TE) Label Switched Paths (LSPs)", RFC 5152,
February 2008.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path
Computation Element (PCE) Communication
Protocol (PCEP)", RFC 5440, March 2009.
[RFC5441] 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", RFC 5441,
April 2009.
[RFC5520] Bradford, R., Vasseur, JP., and A. Farrel,
"Preserving Topology Confidentiality in Inter-
Domain Path Computation Using a Path-Key-Based
Mechanism", RFC 5520, April 2009.
[RFC5521] Oki, E., Takeda, T., and A. Farrel,
"Extensions to the Path Computation Element
Communication Protocol (PCEP) for Route
Exclusions", RFC 5521, April 2009.
[RFC5886] Vasseur, JP., Le Roux, JL., and Y. Ikejiri, "A
Set of Monitoring Tools for Path Computation
Element (PCE)-Based Architecture", RFC 5886,
June 2010.
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[PCE-P2MP-PROCEDURES] Zhao, Q., Dhody, D., Ali, Z., Saad,, T.,
Sivabalan,, S., and R. Casellas, "PCE-based
Computation Procedure To Compute Shortest
Constrained P2MP Inter-domain Traffic
Engineering Label Switched Paths (draft-ietf-
pce-pcep-inter-domain-p2mp-procedures-02)",
February 2012.
[PCE-HIERARCHY-FWK] King, D. and A. Farrel, "The Application of
the Path Computation Element Architecture to
the Determination of a Sequence of Domains in
MPLS and GMPLS.
(draft-ietf-pce-hierarchy-fwk-04)", June 2012.
[PCEP-MIB] Kiran Koushik, A S., Stephan, E., Zhao, Q.,
and D. King, "PCE communication protocol(PCEP)
Management Information Base", July 2010.
[PCE-P2MP-PER-DEST] Dhody, D. and U. Palle, "Supporting explicit-
path per destination in Path Computation
Element Communication Protocol (PCEP) P2MP
Path Request Message. (draft-dhody-pce-pcep-
p2mp-per-destination-01)", Feb 2012.
Authors' Addresses
Dhruv Dhody
Huawei Technologies India Pvt Ltd
Leela Palace
Bangalore, Karnataka 560008
INDIA
EMail: dhruv.dhody@huawei.com
Udayasree Palle
Huawei Technologies India Pvt Ltd
Leela Palace
Bangalore, Karnataka 560008
INDIA
EMail: udayasree.palle@huawei.com
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Ramon Casellas
CTTC - Centre Tecnologic de Telecomunicacions de Catalunya
Av. Carl Friedrich Gauss n7
Castelldefels, Barcelona 08860
SPAIN
EMail: ramon.casellas@cttc.es
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