Network work group Mach Chen
Renhai Zhang
Internet Draft Huawei Technologies Co.,Ltd
Expires: July 2007 January 30, 2007
OSPF Extensions in Support of Inter-AS (G)MPLS TE
draft-chen-ccamp-ospf-interas-te-extension-00.txt
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Abstract
This document describes extensions to the OSPF to support inter-AS
Traffic engineering (TE). It defines OSPF extensions for the flooding
of inter-AS links information which can be used to perform inter-AS
path computation.
Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119.
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Table of Contents
1. Introduction.................................................2
2. Problem statement............................................3
3. Extensions to OSPF...........................................4
3.1. Remote AS number sub-TLV................................4
3.2. Inter-AS Link type......................................5
3.3. Link ID.................................................5
4. Inter-AS links procedure.....................................5
5. Security Considerations......................................5
6. IANA Considerations..........................................6
6.1. Sub-TLVs types..........................................6
6.2. Link types..............................................6
7. References...................................................7
7.1. Normative References....................................7
7.2. Informative References..................................7
Author's Addresses..............................................8
Intellectual Property Statement.................................8
Disclaimer of Validity..........................................9
Copyright Statement.............................................9
Acknowledgment..................................................9
1. Introduction
[OSPF-TE] defines extensions to the OSPF to support intra-area
Traffic Engineering (TE). The extensions provide a way of describing
the Traffic Engineering information and flooding this information
within an area. Type 10 opaque LSA is used to carry such TE
information. Two top-level TLVs are defined in [OSPF-TE]: Router
Address TLV and Link TLV, the Link TLV has several nested sub-TLVs
which describe the TE attribute for a TE enabled link. A node
advertises this TE information only if an IGP adjacency is
established over an intra-area link.
Inter-AS MPLS TE requirements are described in [INTERAS-TE-REQ]. As
described in [INTERAS-TE-REQ], a method SHOULD provide the ability to
compute a path spanning multiple ASes. So a path computation entity
(Head/Tail-end, ASBR or PCE) needs to know the TE information of not
only the links within an AS, but also the links that connect to other
ASes.
In this document, some extensions to [OSPF-TE] are defined in support
of carrying and flooding inter-AS links information for inter-AS
Traffic Engineering. A new sub-TLV is added to the Link TLV and a new
link type is introduced. The detailed definitions and procedures are
provided in the following sections.
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2. Problem statement
As described in [INTERAS-TE-REQ], in the case of establishing an
inter-AS TE LSP which traverses multiple ASes, the signaling protocol
may contain the following elements in the Explicit Route Object(ERO):
-a set of AS numbers as loose hop and/or
-a set of LSRs including ASBRs
In per domain method, when each entry LSR within an AS receives a
PATH message from the upstream AS with the ERO containing a sequence
of ASes, it SHOULD be able to find which LSRs within the local AS are
connected to the downstream AS, therefore compute a TE LSP segment to
that LSR, and pass this PATH message to it. See the below figure for
example:
R1-----R3-----R5-----R6------R9-----R11
| | / \ | |
R2-----R4--- ----R8------R10----R12
<=AS 1=> <==AS 2= > <=AS 3=>
Figure 1: Inter-AS Reference Model
If an inter-AS TE LSP is to be established from R1 within AS 1 to R12
within AS 3, the AS sequence will be traversed as: AS1, AS2 and AS3.
The PATH message is constructed and sent from R1. When R5 within AS 2
receives the PATH message, R5 SHOULD firstly be able to determine
that there are two ASBRs and two inter-AS links connected to AS 3,
then R5 SHOULD be able to choose a feasible route to the entry LSR(R9
or R10) within AS 3. To make these abilities possible for R5, besides
the usual TE database information including the inter-AS TE links
(R6-R9, R8-R10), R5 SHOULD also maintain the following information
for each inter-AS TE link:
-an indication that this is an inter-AS link
-the neighboring AS
-the neighboring ASBR in the neighboring AS
This information is needed throughout the local AS if path
computation function is fully distributed among LSRs within the local
AS.
Another scenario using PCE technique also has the above problem.
[BRPC] defines a PCE-based TE LSP computation method to compute
optimal inter-domain constrained (G)MPLS TE LSPs. In this path
computation method, a set of specific traversed domains are assumed
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to be selected before the computation starts. Each downstream PCE in
domain(i) SHOULD return a VSPT to the upstream PCE in domain(i-1),
where VSPT is a MP2P tree from Boundary Nodes located in domain(i) to
the destination that satisfies the set of required constraints for
the TE LSP (bandwidth, affinities, ...). So a PCE needs to locate
Boundary Nodes that provide connectivity from a specified AS. For
inter-AS TE stated in this document, the PCE MUST have the knowledge
of inter-AS links information to locate the ASBRs connected with
remote ASes.
An extension to IGP is introduced in this draft to flood inter-AS
links information among LSRs within the local AS. BGP extension to
flood this information for PCE is out of scope of this document.
3. Extensions to OSPF
In this document, we use the Type 11 Opaque LSAs, which have an AS
flooding scope. That is, inter-AS TE links SHOULD be flooded within a
whole AS, each router in the AS can receive those inter-AS TE links
and can use such information for inter-AS path computation.
3.1. Remote AS number sub-TLV
As described in [OSPF-TE], the Link TLV describes a single link and
it consists of a set of sub-TLVs. In this document, a new sub-TLV,
Remote AS number sub-TLV is added to the Link TLV when advertising
inter-AS links. The Remote AS number sub-TLV specifies the AS number
of the neighboring AS corresponding to this link.
The Remote AS number sub-TLV is TLV type 18 (which needs to be
confirmed by IANA), and is four octets in length. The format is as
follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote AS Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Remote AS number field has 4 octets, when two octets are used for
AS number in current implementation, the left two octets MUST be set
to zero.
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3.2. Inter-AS Link type
To identify a link to be an inter-AS link, a new Link type, inter-AS
link is specified, the value of inter-AS link type is 3 (which needs
to be confirmed by IANA).
3.3. Link ID
For an inter-AS link, the Link ID is the remote ASBR Router ID
corresponding to this inter-AS link.
4. Inter-AS links procedure
Although there is no OSPF adjacency running over an inter-AS link,
the ASBR SHOULD advertise this link to all nodes within its AS when
TE is enabled on the link and the link is up. When either the link is
down or TE is disabled on the link, the ASBR SHOULD withdraw the
advertisement.
As a result of such advertisement, all nodes in that AS will get
those inter-AS links information. An AS Boundary Connection table
COULD be established to efficiently maintain those information. Each
table entry SHOULD at least consist of Router ID of Local ASBR,
Router ID of remote ASBR, Remote AS number. Take Figure 1 for example
again, AS Boundary Connect table of R5 should include such
information as below:
Remote AS number Local Router ID Remote Router ID
--------------------------------------------------
AS1 R5 R3
AS1 R5 R4
AS3 R6 R9
AS3 R8 R10
Table 1: The AS Boundary Connect table for R5
By looking up this table, a path computation entity can identify an
ASBR to reach the next AS. PCE can also identify all ASBRs connected
to a specified AS.
5. Security Considerations
This extension to OSPF does not change the underlying security issues.
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6. IANA Considerations
6.1. Sub-TLVs types
Value Meaning
18 Remote AS number sub-TLV.
6.2. Link types
Value Meaning
3 inter-AS link type.
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7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[RFC2370] R. Coltun, "The OSPF Opaque LSA Option", RFC2370, July
1998.
[OSPF] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April
1998.
[INTERAS-TE-REQ] Zhang and Vasseur, "MPLS Inter-AS Traffic
Engineering Requirements", RFC4216, November 2005.
[OSPF-TE] Katz, D., Kompella, K., and Yeung, D., "Traffic
Engineering (TE) Extensions to OSPF Version 2", RFC
3630, September 2003.
[CCAMP-INTER-DOMAIN-TE] Ayyangar, A. and J. Vasseur, "Inter domain
GMPLS Traffic Engineering - RSVP-TE extensions",draft-ietf-
ccamp-inter-domain-rsvp-te-04 (work in progress), January
2007.
7.2. Informative References
[INTERAS-TE-REQ] Zhang and Vasseur, "MPLS Inter-AS Traffic
Engineering Requirements", RFC4216, November 2005.
[PER-DOMAIN] Ayyangar, A., Vasseur, J., and Zhang, R., "A Per-domain
path computation method for establishing Inter-domain",
draft-ietf-ccamp-inter-domain-pd-path-comp-03 (work in
progress), August, 2006.
[BRPC] JP. Vasseur, Ed., R. Zhang, N. Bitar, JL. Le Roux, "A Backward
Recursive PCE-based Computation (BRPC) procedure to compute
shortest inter-domain Traffic Engineering Label Switched
Paths ", draft-ietf-pce-brpc-03.txt, Work in Progress,
January 2007.
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Author's Addresses
Mach Chen
Huawei Technologies Co.,Ltd
KuiKe Building, No.9 Xinxi Rd.,
Hai-Dian District
Beijing, 100085
P.R. China
Email: mach@huawei.com
Renhai Zhang
Huawei Technologies Co.,Ltd
KuiKe Building, No.9 Xinxi Rd.,
Hai-Dian District
Beijing, 100085
P.R. China
Email: zhangrenhai@huawei.com
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