PCE Working Group D. Dhody
Internet-Draft U. Palle
Intended status: Standards Track Huawei Technologies India Pvt
Expires: August 12, 2012 Ltd
R. Casellas
CTTC - Centre Tecnologic de
Telecomunicacions de Catalunya
February 9, 2012
Standard Representation Of Domain Sequence
draft-dhody-pce-pcep-domain-sequence-02
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
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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 August 12, 2012.
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Detail Description . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Domains . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Domain-Sequence . . . . . . . . . . . . . . . . . . . . . 5
3.3. Standard Representation . . . . . . . . . . . . . . . . . 6
3.4. Mode of Operation . . . . . . . . . . . . . . . . . . . . 8
3.5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.5.1. Inter-Area Path Computation . . . . . . . . . . . . . 9
3.5.2. Inter-AS Path Computation . . . . . . . . . . . . . . 11
3.5.2.1. Example 1 . . . . . . . . . . . . . . . . . . . . 11
3.5.2.2. Example 2 . . . . . . . . . . . . . . . . . . . . 13
3.5.3. Boundary Node and Inter-AS-Link . . . . . . . . . . . 15
3.5.4. PCE serving multiple domains . . . . . . . . . . . . . 16
3.5.5. P2MP . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.5.6. HPCE . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.5.7. Relationship to PCE Sequence . . . . . . . . . . . . . 18
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
4.1. New IRO Object Type . . . . . . . . . . . . . . . . . . . 19
4.2. Sub-Objects . . . . . . . . . . . . . . . . . . . . . . . 19
5. Security Considerations . . . . . . . . . . . . . . . . . . . 19
6. Manageability Considerations . . . . . . . . . . . . . . . . . 19
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
8.1. Normative References . . . . . . . . . . . . . . . . . . . 19
8.2. Informative References . . . . . . . . . . . . . . . . . . 20
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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
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 Antonymous 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 is 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 Area.
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
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3.3. Standard Representation
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.
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)
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.
[RFC3209] also defines 2 octet AS number.
To support 4 octet AS number [RFC4893] following subobject is
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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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Since the length of Area-id is different for OSPF and ISIS, we
propose different sub-objects.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Area Id (4 bytes) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The length if fixed.
For ISIS, the area-id is of variable length and thus the length of
the Subobject is variable. The Area-id is as described in ISIS by
ISO standard [ISO 10589]. The Length MUST be at least 4, and MUST be
a multiple of 4.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// ISIS Area ID //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The above sub-objects in various combinations can be used to encode
the domain-sequence. When the domain-sequence is used as a
constraint in path computation request it is carried in IRO Domain
Sequence Object Type. The same sub-objects and their encoding can be
used in ERO and path reply message when the domain sequence is
computed from Parent PCE.
All other rules of PCEP objects and message processing is as per
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[RFC5440].
3.4. Mode of Operation
A domain sequence IRO object constraints or defines the domains
involved in a muti-domain path computation, typically involving two
or more collaborative PCEs.
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 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;
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).
The following algorithm can be applied to select the next domain and,
if need be, the PCE responsible for that domain. Note the PCC select
the PCE(1) based on its own domain information.
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START
Get the first Sub-Object S1 from the Domain-Sequence
IF S1's Type is Area (OSPF or ISIS)
IF S1's Domain is same as current PCE's Area
Remove S1 from Domain-Sequence and Goto START
ELSE
Find the next PCE based on S1's Area within the AS
ENDIF
ELSEIF S1's Type is AS (2 or 4 Byte)
IF S1's Domain is same as current PCE's AS
Remove S1 from Domain-Sequence and Goto START
ELSE
Get the next Sub-Object S2 from the Domain-Sequence
IF the S2 is NULL or S2's type is AS
Find the next PCE based on S1's Domain (AS) only
ELSEIF S1's Type is Area
Find the next PCE based on S1's Domain (AS)
and S2's Domain (Area)
ELSE
ENDIF
ENDIF
ENDIF
IF Domain-Sequence is empty or next PCE is not found
Send PCRep with NO-Path
ENDIF
If the Sub-Object is of other type representing Boundary Node or
Inter-As-Link, it is not used to select the next PCE, but used only
while applying BRPC or any other inter-domain procedure.
3.5. Examples
3.5.1. 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.
3.5.2. 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.
3.5.2.1. 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.
3.5.2.2. 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).
3.5.3. 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 | | |
| | | | | | | | | |
+---------+ +---------+ +---------+ +---------+ +---------+
3.5.4. 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.
3.5.5. P2MP
In case of P2MP 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
3.5.6. 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.
3.5.7. 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, which simplifies as explained
below:
Advantages
o All PCE must be aware of all other PCEs in all domain for PCE-
Sequence. There is no clear method for this. In domain-sequence
PCE should be aware of the domains and not all the PCEs serving
the domain. PCE needs to be aware of the neighboring PCEs as done
by discovery protocols.
o There maybe multiple PCE in a domain, the selection of PCE should
not be made at the PCC/PCE(1). This decision is made only at the
neighboring PCE which is aware of state of PCEs via notification
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messages.
o Domain sequence would be compatible to P2P inter-domain BRPC
method as described in [RFC5441].
4. IANA Considerations
4.1. New IRO Object Type
IANA has defined a registry for Domain-Sequence.
IRO Object-Class 10
IRO Object-Type 2
4.2. Sub-Objects
IANA has defined a registry for following sub-objects.
Type Sub-object
TBD AS Number (4 Byte)
TBD OSPF Area id
TBD ISIS Area id
5. Security Considerations
This document specifies a standard representation of domain sequence,
which is used in all inter-domain PCE scenarios as explained in other
RFC and drafts. It does not introduce any new security
considerations.
6. Manageability Considerations
TBD
7. Acknowledgments
We would like to thank Pradeep Shastry, Suresh babu, Quintin Zhao,
Fatai Zhang, Daniel King, Oscar Gonzalez and Chen Huaimo 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.
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[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
Framework for Inter-Domain Multiprotocol Label
Switching Traffic Engineering", RFC 4726,
November 2006.
[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
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Shortest Constrained Inter-Domain Traffic
Engineering Label Switched Paths", RFC 5441,
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.
[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-00)",
October 2011.
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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