PCE Working Group D. Dhody
Internet-Draft U. Palle
Intended status: Experimental Huawei Technologies
Expires: July 3, 2015 R. Casellas
CTTC
December 30, 2014
Standard Representation of Domain-Sequence
draft-ietf-pce-pcep-domain-sequence-07
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. 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 Interior
Gateway Protocol (IGP) area or an Autonomous System (AS). 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 to be used by Path
Computation Elements (PCEs) to compute inter-domain constrained
shortest paths across a predetermined sequence of domains . This
document also defines new subobjects 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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 3, 2015.
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Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Detail Description . . . . . . . . . . . . . . . . . . . . . 5
3.1. Domains . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Domain-Sequence . . . . . . . . . . . . . . . . . . . . . 5
3.3. Standard Representation . . . . . . . . . . . . . . . . . 6
3.4. Include Route Object (IRO) . . . . . . . . . . . . . . . 7
3.4.1. Subobjects . . . . . . . . . . . . . . . . . . . . . 7
3.4.1.1. Autonomous system . . . . . . . . . . . . . . . . 8
3.4.1.2. IGP Area . . . . . . . . . . . . . . . . . . . . 8
3.4.2. Update in IRO specification . . . . . . . . . . . . . 9
3.4.3. IRO for Domain-Sequence . . . . . . . . . . . . . . . 10
3.5. Exclude Route Object (XRO) . . . . . . . . . . . . . . . 11
3.5.1. Subobjects . . . . . . . . . . . . . . . . . . . . . 12
3.5.1.1. Autonomous system . . . . . . . . . . . . . . . . 12
3.5.1.2. IGP Area . . . . . . . . . . . . . . . . . . . . 13
3.6. Explicit Exclusion Route Subobject (EXRS) . . . . . . . . 14
3.7. Explicit Route Object (ERO) . . . . . . . . . . . . . . . 14
4. Other Considerations . . . . . . . . . . . . . . . . . . . . 15
4.1. Inter-Area Path Computation . . . . . . . . . . . . . . . 15
4.2. Inter-AS Path Computation . . . . . . . . . . . . . . . . 17
4.2.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . 17
4.2.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . 19
4.3. Boundary Node and Inter-AS-Link . . . . . . . . . . . . . 21
4.4. PCE Serving multiple Domains . . . . . . . . . . . . . . 21
4.5. P2MP . . . . . . . . . . . . . . . . . . . . . . . . . . 22
4.6. Hierarchical PCE . . . . . . . . . . . . . . . . . . . . 22
4.7. Relationship to PCE Sequence . . . . . . . . . . . . . . 24
4.8. Relationship to RSVP-TE . . . . . . . . . . . . . . . . . 24
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
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5.1. New Subobjects . . . . . . . . . . . . . . . . . . . . . 25
5.2. Error Object Field Values . . . . . . . . . . . . . . . . 25
6. Security Considerations . . . . . . . . . . . . . . . . . . . 25
7. Manageability Considerations . . . . . . . . . . . . . . . . 26
7.1. Control of Function and Policy . . . . . . . . . . . . . 26
7.2. Information and Data Models . . . . . . . . . . . . . . . 26
7.3. Liveness Detection and Monitoring . . . . . . . . . . . . 26
7.4. Verify Correct Operations . . . . . . . . . . . . . . . . 26
7.5. Requirements On Other Protocols . . . . . . . . . . . . . 26
7.6. Impact On Network Operations . . . . . . . . . . . . . . 27
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 27
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
9.1. Normative References . . . . . . . . . . . . . . . . . . 27
9.2. Informative References . . . . . . . . . . . . . . . . . 27
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 backward recursive path computation (BRPC) mechanism [RFC5441]
also defines a PCE-based path computation procedure to compute inter-
domain constrained path for (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. Also for inter-domain
point-to-multi-point (P2MP) tree computation, [RFC7334] assumes the
domain-tree is known in priori.
The list of domains (Domain-Sequence) in point-to-point (P2P) or a
domain tree in point-to-multipoint (P2MP) is usually a constraint in
inter-domain path computation procedure. A PCE determines the next
PCE to forward the request based on the Domain-Sequence. In a multi-
domain path computation, a Path Computation Client (PCC) MAY indicate
the sequence of domains to be traversed using the Include Route
Object (IRO) defined in [RFC5440].
When the sequence of domains is not known in advance, the
Hierarchical PCE (H-PCE) [RFC6805] architecture and mechanisms can be
used to determine the Domain-Sequence.
This document defines a standard way to represent and encode a
Domain-Sequence in various scenarios including P2P LSP, P2MP LSP, and
use of H-PCE.
The Domain-Sequence (the set of domains traversed to reach the
destination domain) is either administratively predetermined or
discovered by some means like H-PCE.
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[RFC5440] defines the Include Route Object (IRO) and the Explicit
Route Object (ERO). [RFC5521] defines the Exclude Route Object (XRO)
and the Explicit Exclusion Route Subobject (EXRS). The use of
Autonomous System (AS) (albeit with a 2-Byte AS number) as an
abstract node representing a domain is defined in [RFC3209], this
document specifies new subobjects to include or exclude domains
including IGP area or an Autonomous Systems (4-Byte as per
[RFC6793]).
Further, the domain identifier may simply act as delimiter to specify
where the domain boundary starts and ends in some cases.
This is a companion document to Resource ReserVation Protocol -
Traffic Engineering (RSVP-TE) extensions for the domain identifiers
[DOMAIN-SUBOBJ].
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.
AS: Autonomous System.
ASBR: Autonomous System Boundary Router.
BN: Boundary Node, Can be an ABR or ASBR.
BRPC: Backward Recursive Path Computation
Domain: As per [RFC4655], any collection of network elements within
a common sphere of address management or path computational
responsibility. Examples of domains include Interior Gateway
Protocol (IGP) area and Autonomous System (AS).
Domain-Sequence: An ordered sequence of domains traversed to reach
the destination domain.
ERO: Explicit Route Object
H-PCE: Hierarchical PCE
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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.
XRO: Exclude Route Object
3. Detail Description
3.1. Domains
[RFC4726] and [RFC4655] define domain 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 AS or an IGP area.
Each AS can be made of several IGP areas. In order to encode a
Domain-Sequence, it is required to uniquely identify a domain in the
Domain-Sequence. A domain can be uniquely identified by area-id or
AS number or both.
3.2. Domain-Sequence
A Domain-Sequence is an ordered sequence of domains traversed to
reach the destination domain.
A Domain-Sequence can be applied as a constraint and carried in a
path computation request to PCE(s). A Domain-Sequence can also be
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the result of a path computation. For example, in the case of H-PCE
[RFC6805] Parent PCE MAY send the Domain-Sequence as a result in a
path computation reply.
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 a list of
Domain-Sequences.
A Domain-Sequence enables a PCE to select the next domain and the PCE
serving that domain to forward the path computation request based on
the domain information.
A PCC or PCE MAY add an additional constraint covering which Boundary
Nodes (ABR or ASBR) or Border links (Inter-AS-links) 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:
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 then be an input to the BRPC procedure [RFC6805];
3. by a PCC (or PCE) to constraint the domains used in a H-PCE path
computation, explicitly specifying which domains to be expanded;
4. by a PCE in the per-domain path computation model [RFC5152] to
identify the next domain;
3.3. Standard Representation
Domain-Sequence MAY appear in PCEP messages, notably in -
o Include Route Object (IRO): As per [RFC5440], used to specify set
of network elements that MUST be traversed. The subobjects in IRO
are used to specify the Domain-Sequence that MUST be traversed to
reach the destination.
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o Exclude Route Object (XRO): As per [RFC5521], used to specify
certain abstract nodes that MUST be excluded from whole path. The
subobjects in XRO are used to specify certain domains that MUST be
avoided to reach the destination.
o Explicit Exclusion Route Subobject (EXRS): As per [RFC5521], used
to specify exclusion of certain abstract nodes between a specific
pair of nodes. EXRS are a subobject inside the IRO. These
subobjects are used to specify the domains that must be excluded
between two abstract nodes.
o Explicit Route Object (ERO): As per [RFC5440], used to specify a
computed path in the network. For example, in the case of H-PCE
[RFC6805], a Parent PCE MAY send the Domain-Sequence as a result
in a path computation reply using ERO.
3.4. Include Route Object (IRO)
As per [RFC5440], IRO (Include Route Object) can be used to specify
that the computed path MUST traverse a set of specified network
elements or abstract nodes.
3.4.1. Subobjects
Some subobjects are defined in [RFC3209], [RFC3473], [RFC3477] and
[RFC4874], but new subobjects related to Domain-Sequence are needed.
The following subobject types are used in IRO.
Type Subobject
1 IPv4 prefix
2 IPv6 prefix
4 Unnumbered Interface ID
32 Autonomous system number (2 Byte)
33 Explicit Exclusion (EXRS)
This document extends the above list to support 4-Byte AS numbers and
IGP Areas.
Type Subobject
TBD1 Autonomous system number (4 Byte)
TBD2 OSPF Area id
TBD3 ISIS Area id
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3.4.1.1. Autonomous system
[RFC3209] already defines 2 byte AS number.
To support 4 byte AS number as per [RFC6793] 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 defined in [RFC3209]
and usage in IRO subobject updated in [IRO-UPDATE].
Type: (TBD1 by IANA) indicating a 4-Byte AS Number.
Length: 8 (Total length of the subobject in bytes).
Reserved: Zero at transmission, ignored at receipt.
AS-ID: The 4-Byte AS Number. Note that if 2-Byte 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.
3.4.1.2. 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 is encoded
as follows:
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 defined in [RFC3209]
and usage in IRO subobject updated in [IRO-UPDATE].
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Type: (TBD2 by IANA) indicating a 4-Byte OSPF Area ID.
Length: 8 (Total length of the subobject in bytes).
Reserved: Zero at transmission, ignored at receipt.
OSPF Area Id: The 4-Byte 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 [ISO10589]. The subobject is encoded as follows:
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 defined in [RFC3209]
and usage in IRO subobject updated in [IRO-UPDATE].
Type: (TBD3 by IANA) indicating IS-IS Area ID.
Length: Variable. As per [RFC3209], the total length of the
subobject in bytes, including the L, Type and Length fields. 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).
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-byte boundary.
3.4.2. Update in IRO specification
[RFC5440] describes IRO as an optional object used to specify that
the computed path MUST traverse a set of specified network elements.
It further state that the L bit of such subobject has no meaning
within an IRO. It did not mention if IRO is an ordered or un-ordered
list of subobjects.
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An update to IRO specification [IRO-UPDATE] makes IRO as an ordered
list as well as support for loose bit (L-bit).
The use IRO for Domain-Sequence assumes the updated specification for
IRO as per [IRO-UPDATE].
3.4.3. IRO for Domain-Sequence
Some subobjects for the IRO are defined in [RFC3209], [RFC3473],
[RFC3477], and [RFC4874]; further some new subobjects related to
Domain-Sequence are also added in this document as mentioned in
Section 3.4.
The subobject type for IPv4, IPv6, and unnumbered Interface ID can be
used to specify Boundary Nodes (ABR/ASBR) and Inter-AS-Links. The
subobject type for the AS Number (2 or 4 Byte) and the IGP Area are
used to specify the domain identifiers in the Domain-Sequence.
The IRO MAY have both intra-domain (from the context of the ingress
PCC) and inter-domain (Domain-Sequence) subobjects in a sequence in
which they must be traversed in the computed path.
Thus an IRO, comprising of subobjects that represents a Domain-
Sequence, define the domains involved in an inter-domain path
computation, typically involving two or more collaborative PCEs.
A Domain-Sequence can have varying degrees of granularity. It is
possible to have a Domain-Sequence composed of, uniquely, AS
identifiers. It is also possible to list the involved IGP 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 an IRO to encode the Domain-Sequence, so that the
cooperating PCEs should compute an inter-domain shortest constrained
path across the specified sequence of domains.
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.
If a PCE 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
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with Error-Type TBD4 "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.
PCE 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 the Domain-Sequence in order identified by the
subobjects 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 request.
A successful path computation reported in a path computation reply
message (PCRep) MUST include an ERO to specify the path that has been
computed as specified in [RFC5440] following the sequence of domains.
In a PCRep, PCE MAY also supply IRO (with Domain-Sequence
information) with the NO-PATH object indicating that the set of
elements (domains) of the request's IRO prevented the PCEs from
finding a path.
Selection of the next domain and the PCE serving that domain is
dependent on the domain subobjects (AS and IGP area) in the IRO.
Note that a particular domain in the Domain-Sequence can be
identified by :-
o A single IGP Area: Only the IGP (OSPF or ISIS) Area subobject is
used to identify the next domain. (Refer Figure 1)
o A single AS: Only the AS subobject is used to identify the next
domain. (Refer Figure 2)
o Both an AS and an IGP Area: AS and Area in combination are used to
identify the next domain. In this case the order is AS Subobject
followed by Area. (Refer Figure 3)
The Subobjects representing an internal node, a Boundary Node or an
Inter-AS-Link MAY also influence the selection of the path.
3.5. Exclude Route Object (XRO)
The Exclude Route Object (XRO) [RFC5521] is an optional object used
to specify exclusion of certain abstract nodes or resources from the
whole path.
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3.5.1. Subobjects
The following subobject types are defined to be used in XRO as
defined in [RFC3209], [RFC3477], [RFC4874], and [RFC5521].
Type Subobject
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
This document extends the above list to support 4-Byte AS numbers and
IGP Areas.
Type Subobject
TBD1 Autonomous system number (4 Byte)
TBD2 OSPF Area id
TBD3 ISIS Area id
3.5.1.1. Autonomous system
The new subobjects to support 4 byte AS and IGP (OSPF / ISIS) Area
MAY also be used in the XRO to specify exclusion of certain domains
in the path computation procedure.
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The X-bit indicates whether the exclusion is mandatory or desired.
0: indicates that the AS specified MUST be excluded from the path
computed by the PCE(s).
1: indicates that the AS specified SHOULD be avoided 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.
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All other fields are consistent with the definition in Section 3.4.
3.5.1.2. 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 is encoded
as follows:
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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The X-bit indicates whether the exclusion is mandatory or desired.
0: indicates that the OSFF Area specified MUST be excluded from the
path computed by the PCE(s).
1: indicates that the OSFF Area specified SHOULD be avoided 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.
All other fields are consistent with the definition in Section 3.4.
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 [ISO10589]. The subobject is encoded as follows:
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 //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The X-bit indicates whether the exclusion is mandatory or desired.
0: indicates that the ISIS Area specified MUST be excluded from the
path computed by the PCE(s).
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1: indicates that the ISIS Area specified SHOULD be avoided 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.
All other fields are consistent with the definition in Section 3.4.
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 TBD4 "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].
3.6. Explicit Exclusion Route Subobject (EXRS)
Explicit Exclusion Route Subobject (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 byte 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].
3.7. Explicit Route Object (ERO)
The Explicit Route Object (ERO) [RFC5440] is used to specify a
computed path in the network. PCEP ERO subobject types correspond to
RSVP-TE ERO subobject types as defined in [RFC3209], [RFC3473],
[RFC3477], [RFC4873], [RFC4874], and [RFC5520].
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Type Subobject
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
This document extends the above list to support 4-Byte AS numbers and
IGP Areas.
Type Subobject
TBD1 Autonomous system number (4 Byte)
TBD2 OSPF Area id
TBD3 ISIS Area id
The new subobjects to support 4 byte 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.
In case of Hierarchical PCE [RFC6805], a Parent PCE MAY be requested
to find the Domain-Sequence. Refer example in Section 4.6.
The format of the new ERO subobjects is similar to new IRO
subobjects, refer Section 3.4.
4. Other Considerations
The examples in this section are for illustration purposes only; to
highlight how the new subobjects may be encoded.
4.1. Inter-Area Path Computation
In an inter-area path computation where the ingress and the egress
nodes belong to different IGP areas within the same AS, the Domain-
Sequence MAY be represented using a ordered list of Area subobjects.
The AS number MAY be 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 |
+------------------+ +--------------------+
Figure 1: Inter-Area Path Computation
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AS Number is 100.
This could be represented in the <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.
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 subobjects. The Domain-Sequence MAY further include
decomposed area information in Area subobjects.
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 | |
| +------+ | | +------+ |
| | | |
+------------------------+ | |
+---------------------------------+
Figure 2: Inter-AS Path Computation
Both AS are made of Area 0.
This could be represented in the <IRO> as:
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+---------+ +---------+ +---------+
|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 subobject is optional and it MAY be skipped. PCE should be able
to understand both notations.
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.
|
| +-------------+ +----------------+
| |Area 2 | |Area 4 |
| | +--+| | +--+ |
| | | || | | | |
| | +--+ +--+| | +--+ +--+ |
| | | | | | | | |
| | *--+ | | +--+ |
| | / +--+ | | +--+ |
| |/ | | | | | | |
| / +--+ | | +--+ +--+ |
| /| +--+ |+--------------+| | | |
|/ | | | ++-+ +-++ +--+ |
+-------------+/ | +--+ || | | || |
| /| | ++-+ +-++ |
| +--*|| +-------------+| |+----------------+
| | ||| | +--+ |
| +--+|| | | | |
| +--+ || | +--+ |
| | | || | |
| +--+ || | |
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| || | +--+ |
|+--+ || | | | |
|| | || | +--+ |
|+--+ || | |
| || | +--+ |
| +--+ || +------------+ | | | |+----------------+
| | | || |Area 3 +-++ +--+ +-++ Area 5 |
| +--+ || | | || | || |
| || | +-++ +-++ |
| +--+|| | +--+ | | Area 0 || +--+ |
| | ||| | | | | +--------------+| | | |
| +--*|| | +--+ | | +--+ |
| \| | | | +--+ |
|Area 1 |\ | +--+ | | +--+ | | |
+-------------+|\ | | | | | | | +--+ |
| \| +--+ +--+ | +--+ |
| \ | | | |
| |\ +--+ | +--+ |
| | \ +--+ | | | | |
| | \| | | | +--+ |
| | *--+ | | |
| | | | |
| +------------+ +----------------+
|
|
AS 100 | AS 200
|
Figure 3: Inter-AS Path Computation
The Domain-Sequence can be carried in the 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 |
| | | | | | | | | | | | | |
+-------+ +-------+ +-------+ +-------+ +-------+ +-------+ +-------+
The combination of both an AS and an Area uniquely identify a domain
in the Domain-Sequence.
Note that an Area domain identifier always belongs to the previous AS
that appears before it or, if no AS subobjects are present, it is
assumed to be the current AS.
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If the area information cannot be provided, PCE MAY forward the path
computation request to the next PCE based on AS alone. If multiple
PCEs are responsible, PCE MAY apply local policy to select the next
PCE.
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 subobjects.
Boundary Nodes (ABR / ASBR) can be encoded using the IPv4 or IPv6
prefix subobjects usually the loopback address of 32 and 128 prefix
length respectively. An Inter-AS link can be encoded using the IPv4
or IPv6 prefix subobjects or unnumbered interface subobjects.
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 || | | |
| | | | | || | | |
+---------+ +---------+ +---------++---------+ +---------+
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 | | |
| | | | | | | | | |
+---------+ +---------+ +---------+ +---------+ +---------+
4.4. PCE Serving multiple Domains
A single PCE MAY be responsible for multiple domains; for example PCE
function deployed on an ABR. A PCE which can support 2 adjacent
domains can internally handle this situation without any impact on
the neighbouring domains.
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4.5. P2MP
In case of inter-domain P2MP path computation, (Refer [RFC7334]) 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])
4.6. Hierarchical PCE
As per [RFC6805], 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
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In H-PCE, the Ingress PCE 'PCE(1)' can request the parent PCE to
determine the Domain-Sequence and return it in the PCEP response,
using the ERO Object. The ERO can contain an ordered sequence of
subobjects such as AS and Area (OSPF/ISIS) subobjects. In this case,
the Domain-Sequence appear 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 |
| | | | | | | | | |
| | | | | | | | | |
+---------+ +---------+ +---------+ +---------+ +---------+
4.7. Relationship to PCE Sequence
Instead of a Domain-Sequence, a sequence of PCEs MAY be enforced by
policy on the PCC, and this constraint can be carried in the PCReq
message (as defined in [RFC5886]).
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.
4.8. Relationship to RSVP-TE
[RFC3209] already describes the notion of abstract nodes, where an
abstract node is a group of nodes whose internal topology is opaque
to the ingress node of the LSP. It further defines a subobject for
AS but with a 2-Byte AS Number.
[DOMAIN-SUBOBJ] extends the notion of abstract nodes by adding new
subobjects for IGP Areas and 4-byte AS numbers. These subobjects MAY
be included in Explicit Route Object (ERO), Exclude Route object
(XRO) or Explicit Exclusion Route Subobject (EXRS) in RSVP-TE.
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In any case subobject type defined in RSVP-TE are identical to the
subobject type defined in the related documents in PCEP.
5. IANA Considerations
5.1. New Subobjects
The "PCEP Parameters" registry contains a subregistry "PCEP Objects"
with an entry for the Include Route Object (IRO), Exclude Route
Object (XRO) and Explicit Route Object (ERO). IANA is requested to
add further subobjects as follows:
7 ERO
10 IRO
17 XRO
Subobject Type Reference
TBD1 4 byte AS number [This I.D.]
TBD2 OSPF Area ID [This I.D.]
TBD3 IS-IS Area ID [This I.D.]
5.2. 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
TBD4 "Unrecognized subobject" [This I.D.]
Error-Value: type code
6. Security Considerations
This document specifies a standard representation of Domain-Sequence
and new subobjects, which MAY be used in inter-domain PCE scenarios
as explained in other RFC and drafts. The new subobjects 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
operator with the ability to route around vulnerable parts of the
network and may be used to increase overall network security.
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7. Manageability Considerations
7.1. 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
subobjects 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.
7.2. Information and Data Models
A MIB module for management of the PCEP is being specified in a
separate document [RFC7420]. 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.
7.3. 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].
7.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC5440].
7.5. Requirements On Other Protocols
In case of per-domain path computation [RFC5152], where the full path
of an inter-domain TE LSP cannot be, or is not determined at the
ingress node, a signaling message may use the domain identifiers.
The Subobjects defined in this document SHOULD be supported by RSVP-
TE. [DOMAIN-SUBOBJ] extends the notion of abstract nodes by adding
new subobjects for IGP Areas and 4-byte AS numbers.
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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7.6. 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].
8. 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 Sandeep Boina and Avantika for their
useful comments and suggestions.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC5521] Oki, E., Takeda, T., and A. Farrel, "Extensions to the
Path Computation Element Communication Protocol (PCEP) for
Route Exclusions", RFC 5521, April 2009.
[RFC6805] 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", RFC 6805, November
2012.
9.2. 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.
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[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 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.
[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.
[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.
[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.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793, December
2012.
[RFC7334] Zhao, Q., Dhody, D., King, D., Ali, Z., and R. Casellas,
"PCE-Based Computation Procedure to Compute Shortest
Constrained Point-to-Multipoint (P2MP) Inter-Domain
Traffic Engineering Label Switched Paths", RFC 7334,
August 2014.
[RFC7420] Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
Hardwick, "Path Computation Element Communication Protocol
(PCEP)", RFC 7420, December 2014.
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[PCE-P2MP-PER-DEST]
Dhody, D., Palle, U., and V. Kondreddy, "Supporting
explicit inclusion or exclusion of abstract nodes for a
subset of P2MP destinations in Path Computation Element
Communication Protocol (PCEP). (draft-dhody-pce-pcep-p2mp-
per-destination)", September 2014.
[DOMAIN-SUBOBJ]
Dhody, D., Palle, U., Kondreddy, V., and R. Casellas,
"Domain Subobjects for Resource ReserVation Protocol -
Traffic Engineering (RSVP-TE). (draft-ietf-teas-rsvp-te-
domain-subobjects-00)", December 2014.
[IRO-UPDATE]
Dhody, D., "Update to Include Route Object (IRO)
specification in Path Computation Element communication
Protocol (PCEP. (draft-dhody-pce-iro-update-02)", December
2014.
[ISO10589]
ISO, "Intermediate system to Intermediate system routing
information exchange protocol for use in conjunction with
the Protocol for providing the Connectionless-mode Network
Service (ISO 8473)", ISO/IEC 10589:2002, 1992.
Authors' Addresses
Dhruv Dhody
Huawei Technologies
Leela Palace
Bangalore, Karnataka 560008
India
EMail: dhruv.ietf@gmail.com
Udayasree Palle
Huawei Technologies
Leela Palace
Bangalore, Karnataka 560008
India
EMail: udayasree.palle@huawei.com
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Ramon Casellas
CTTC
Av. Carl Friedrich Gauss n7
Castelldefels, Barcelona 08860
Spain
EMail: ramon.casellas@cttc.es
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