PCE Working Group D. Dhody
Internet-Draft U. Palle
Intended status: Standard Huawei Technologies India Pvt Ltd
Expires: February 25, 2012 R. Casellas
CTTC - Centre Tecnologic de
Telecomunicacions de Catalunya
August 24, 2011
Standard Representation Of Domain Sequence
draft-dhody-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 of domain sequence that can be
utilized in all PCE deployment scenarios.
Status of this Memo
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This Internet-Draft will expire on February 25, 2012.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Detail Description . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Domains . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Standard Representation . . . . . . . . . . . . . . . . . 5
3.3. Deployment Scenarios . . . . . . . . . . . . . . . . . . . 6
3.3.1. Only AS . . . . . . . . . . . . . . . . . . . . . . . 6
3.3.2. Only Area . . . . . . . . . . . . . . . . . . . . . . 8
3.3.3. Mix of AS and Area . . . . . . . . . . . . . . . . . . 10
3.3.4. PCE serving multiple domains . . . . . . . . . . . . . 12
3.3.5. P2MP . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3.6. HPCE . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.3.7. Domain Seq V/s PCE Seq . . . . . . . . . . . . . . . . 14
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
5. Security Considerations . . . . . . . . . . . . . . . . . . . 15
6. Manageability Considerations . . . . . . . . . . . . . . . . . 15
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Normative References . . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . . 15
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1. Introduction
RFC 5441 [A Backward-Recursive PCE-Based Computation (BRPC) Procedure
to Compute Shortest Constrained Inter-Domain Traffic Engineering
Label Switched Paths] mentions -
"The sequence of domains to be traversed is either administratively
predetermined or discovered by some means that is outside of the
scope of this document. The PCC MAY indicate the sequence of domains
to be traversed using the Include Route Object (IRO) defined in
[RFC5440] so that it is available to all PCEs."
This document proposes a standard way to represent domain sequence
using IRO in various deployment scenarios.
It further gives examples of various deployment scenario including
P2P, P2MP and HPCE.
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.
AS: Autonomous System.
ASBR: Autonomous System Boundary Router.
BN: Boundary Node, Can be an ABR or ASBR.
BRPC: Backward Recursive Path Computation
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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: The sequence of domains for a path.
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.
3. Detail Description
3.1. Domains
A domain is any collection of network elements within a common sphere
of address management or path computation responsibility. Examples
of domains include IGP areas or Autonomous Systems (ASes). To
uniquely identify a domain in the domain sequence both AS and Area-id
is important.
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3.2. Standard Representation
The IRO (Include Route Object) is used to specify the domain sequence
that the computed inter-domain path MUST traverse.
IRO Object-Class is 10.
IRO Object-Type is 1.
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.
The following sub-object types are used.
Type Sub-object
32 Autonomous system number (2 Byte) [RFC 3209]
TBD Autonomous system number (4 Byte)
TBD OSPF Area id
TBD ISIS Area id
[RFC 3209] define 2 octet AS number.
To support 4 octet AS number [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) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Since the length of Area-id is different for OSPF and ISIS, we
propose different sub-objects.
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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. 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 //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3.3. Deployment Scenarios
3.3.1. Only AS
Considering each AS to be made of a single area, in this scenario the
area MAY be skipped in the domain sequence. The domain sequence
could be represented with just AS numbers.
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+---------------------------------+
|AS 200 |
| +------+ |
| | | |
+------------------------+ | | | +------+ |
| AS 100 | | +------+ | | |
| +------+ | | +------+ | | |
| | +-+-----+-+ | +------+ |
| | | | | | | |
| +------+ | | +------+ |
| +------+ | | +------+ |
| | | | | | | |
| | | | | | | |
| +------+ | | +------+ |
| | | |
| +------+ | | +------+ |
| | +-+-----+-+ | +------+ |
| | | | | | | | | |
| +------+ | | +------+ | | |
| | | +------+ |
| | | |
| | | |
| +------+ | | +------+ |
| | | | | | | |
| |PCE | | | |PCE | |
| +------+ | | +------+ |
| | | |
+------------------------+ | |
+---------------------------------+
Both AS are made of Area 0.
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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.
3.3.2. Only Area
Consider a case where both end of LSP belong to different area but
within the same AS, this could be represented in domain sequence
using the AREA sub-object. AS number MAYBE skipped.
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+-------------------+ +-------------------+
| | | |
| +--+ | | +--+ |
| +--+ | | | | | | |
| | | +--+ | | +--+ +--+ |
| +--* + + | | |
| | | +--+ |
| *--+ + + |
| | | | | +--+ |
| +--+ | | | | |
| |+--------------------------+| +--+ |
| ++++ +-++ |
| |||| +--+ | || |
| Area 2 ++++ | | +-++ Area 4 |
+-------------------+| +--+ |+-------------------+
| |
| +--+ |
| +--+ | | |
| | | +--+ |
| +--+ |
| |
| |
| |
| |
| +--+ |
| | | |
| +--+ |
+------------------+| |+--------------------+
| ++-+ +-++ |
| || | | || |
| ++-+ Area 0 +-++ |
| |+--------------------------+| +--+ |
| +--+ | | | | |
| | | | | +--+ |
| +--+ +--+ | | |
| | | + + +--+ |
| +--+ | | | | |
| + + +--+ |
| +--+ | | |
| | | | | +--+ |
| +--+ | | | | |
| | | +--+ |
| | | |
| Area 1 | | Area 5 |
+------------------+ +--------------------+
AS Number is 100.
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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.
3.3.3. Mix of AS and Area
In inter-AS case where an AS is further made up of multiple areas,
both AS number and area should be a part of domain sequence.
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|
| +-------------+ +----------------+
| |Area 2 | |Area 4 |
| | +--+| | +--+ |
| | | || | | | |
| | +--+ +--+| | +--+ +--+ |
| | | | | | | | |
| | *--+ | | +--+ |
| | / +--+ | | +--+ |
| |/ | | | | | | |
| / +--+ | | +--+ +--+ |
| /| +--+ |+--------------+| | | |
|/ | | | ++-+ +-++ +--+ |
+-------------+/ | +--+ || | | || |
| /| | ++-+ +-++ |
| +--*|| +-------------+| |+----------------+
| | ||| | +--+ |
| +--+|| | | | |
| +--+ || | +--+ |
| | | || | |
| +--+ || | |
| || | +--+ |
|+--+ || | | | |
|| | || | +--+ |
|+--+ || | |
| || | +--+ |
| +--+ || +------------+ | | | |+----------------+
| | | || |Area 3 +-++ +--+ +-++ Area 5 |
| +--+ || | | || | || |
| || | +-++ +-++ |
| +--+|| | +--+ | | Area 0 || +--+ |
| | ||| | | | | +--------------+| | | |
| +--*|| | +--+ | | +--+ |
| \| | | | +--+ |
|Area 1 |\ | +--+ | | +--+ | | |
+-------------+|\ | | | | | | | +--+ |
| \| +--+ +--+ | +--+ |
| \ | | | |
| |\ +--+ | +--+ |
| | \ +--+ | | | | |
| | \| | | | +--+ |
| | *--+ | | |
| | | | |
| +------------+ +----------------+
|
|
As 100 | AS 200
|
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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.
3.3.4. 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.
3.3.5. P2MP
In case of P2MP the path domain tree is nothing but a series of
Domain-Seq, as shown in the below figure:
D1-D3-D6, D1-D3-D5 and D1-D2-D4.
D1
/ \
D2 D3
/ / \
D4 D5 D6
The same domain sequence are carried in IRO as explained above.
3.3.6. HPCE
Consider a case as shown below consisting of child and parent PCE.
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+--------+
| Parent |
| PCE |
+--------+
+-------------------+ +-------------------+
| +--+ | | +--+ |
| +--+ | | | | | | |
| | | +--+ | | +--+ +--+ |
| +--* + + | | |
| | | +--+ |
| *--+ + + |
| | | | | +--+ |
| +--+ | | | | |
| |+--------------------------+| +--+ |
| ++++ +-++ |
| |||| +--+ | || |
| Area 2 ++++ | | +-++ Area 4 |
+-------------------+| +--+ |+-------------------+
| +--+ |
| +--+ | | |
| | | +--+ |
| +--+ |
| |
| +--+ |
| | | |
| +--+ |
+------------------+| |+--------------------+
| ++-+ +-++ |
| || | | || |
| ++-+ Area 0 +-++ |
| |+--------------------------+| +--+ |
| +--+ | | | | |
| | | | | +--+ |
| +--+ +--+ | | |
| | | + + +--+ |
| +--+ | | | | |
| + + +--+ |
| +--+ | | |
| | | | | +--+ |
| +--+ | | | | |
| | | +--+ |
| Area 1 | | Area 5 |
+------------------+ +--------------------+
In HPCE implementation PCE(1) can request the parent PCE to determine
the domain path and return in the PCRep in form of ERO. The
Subobject would be AS and Area (OSPF/ISIS). So in this case, the
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reply would carry the 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 |
| | | | | | | | | |
| | | | | | | | | |
+---------+ +---------+ +---------+ +---------+ +---------+
3.3.7. Domain Seq V/s PCE Seq
[PCE-P2MP-PROCEDURES] introduces the concept of PCE-Sequence, where a
sequence of PCE based on the domain sequence should be decided and
attached in the PCReq at the very beginning of path computation. It
is much simpler and advantageous to carry only domain-sequence rather
than PCE-Sequence.
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
shouldn't be made at the PCC/PCE(1). This decision is made only
at the neighboring PCE which is completely aware of states of PCE
via notification messages.
o Domain sequence would be compatible to P2P inter-domain BRPC
method as described in RFC 5441.
There is no need for PCE-Sequence and it doesn't give any benefits
over Domain Seq.
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4. IANA Considerations
IANA has defined a registry for OSPF and ISIS Area sub-object.
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 and
Chen Huaimo for their useful comments and suggestions.
8. References
8.1. Normative References
[ISO] "Intermediate System to Intermediate System
Intra-Domain Routeing Exchange Protocol for
use in Conjunction with the Protocol for
Providing the Connectionless-mode Network
Service" ISO/IEC 10589:2002 Second Edition
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", March 1997.
8.2. Informative References
[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", September 2010.
[PCE-P2MP-PROCEDURES] Zhao, Q., Ali, Z., Saad,, T., and D. King,
"PCE-based Computation Procedure To Compute
Shortest Constrained P2MP Inter-domain Traffic
Engineering Label Switched Paths",
January 2011.
[RFC 3209] Awduche, D., Berger, L., Gan, D., Li, T.,
Srinivasan, V., and G. Swallow, "RSVP-TE:
Extensions to RSVP for LSP Tunnels",
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December 2001.
[RFC 4893] Vohra, Q. and E. Chen, "BGP Support for Four-
octet AS Number Space", May 2007.
[RFC5440] Ayyangar, A ., Farrel, A ., Oki, E., Atlas,
A., Dolganow, A., Ikejiri, Y., Kumaki, K.,
Vasseur, J., and J. Roux, "Path Computation
Element (PCE) communication Protocol (PCEP)",
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", April 2009.
Authors' Addresses
Dhruv Dhody
Huawei Technologies India Pvt Ltd
Leela Palace
Bangalore, Karnataka 560008
INDIA
EMail: dhruvd@huawei.com
Udayasree Palle
Huawei Technologies India Pvt Ltd
Leela Palace
Bangalore, Karnataka 560008
INDIA
EMail: udayasreepalle@huawei.com
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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