Subject: Re: constraint-based routing algorithms

From: Yakov Rekhter <[email-masked]>
Date: Sat, 16 Jun 2001 18:43:58 -0700

Robert,

> To give you a very short answer you are correct that scope of flooding
> is limited to given area/level. Therefor to establish the inter-area LSP
> your headends will not have enough information to compute full end to
> end ERO. There are main two ways to solve it:
> 
> Online: By means of loose ERO (you indicate via hops or areas) and relay
> on the ABRs to compute it's own part of the ERO.
> 
> Offline: By means of offline server running CSPF which would be
> receiving information about TE topology from multiple areas. 
> 
> There is of course a number of issues with multiarea TEs so please wait
> for the soon to be published ID for more in depth clarification.

While waiting for "the soon to be published ID", one may also look
at draft-kompella-mpls-multiarea-te-01.txt for some of the
possible solutions.

Yakov.

---

From: Dimitri Papadimitriou <[email-masked]>
Date: Sun, 17 Jun 2001 12:35:59 +0200

Robert,

To complete somewhat the description of available ID given by Yakov, 
you could also take a look on the following documents:

1) The draft: draft-venkatachalam-ospf-traffic-01.txt 

This document describes the OSPF "Traffic Engineering Summary LSA"
and its support to enable traffic engineering across area boundaries.
This document describes the traffic engineering (TE) summary LSA that
will be originated by the Area Border Router (ABR) into an area. This 
summary LSA is a type-10 opaque LSA, that will be flooded within the 
area. The functionality of the TE summary LSA is similar to that of 
the summary LSA of standard OSPF, but in addition it carries the 
traffic engineering metrics to the remote destination (IP network or 
ASBR).

2) The draft: draft-venkatachalam-interarea-mpls-te-01.txt   

A Framework for the LSP Setup Across IGP Areas for MPLS Traffic
Engineering This draft propose an architecture for the inter-area LSP 
setup based on criteria (combination of constraints). It derives 
architectural requirements for the routing protocols, signaling 
protocols and the MIBs to support such an idea. Demonstration is made 
that such a mechanism will reduce the crankback during LSP setup. A 
possible outline of the modifications to the CSPF algorithm and 
examples are presented. The companion document (see below) elaborates
on the extensions required for such architecture.

The companion draft is:
draft-dharanikota-interarea-mpls-te-ext-01.txt           
This document proposes the extensions required to the routing protocols, 
signaling protocols, and the MIB to support the idea of inter-area LSPs. 
The companion document (see above) provides the architectural
requirements 
for such a concept. This document also provides the signaling extensions 
to support the crankback as defined in the architecture document.

Regards,
Dimitri.

Yakov Rekhter wrote:
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---

From: "Sudhakar Ganti" <[email-masked]>
Date: Mon, 18 Jun 2001 09:26:16 -0400

For multi-area TE, also look at the following drafts:

1)draft-ash-ccamp-multi-area-te-reqmts-00.txt
2)draft-lee-mpls-te-exchange-00.txt
3)draft-lee-mpls-path-request-00.txt

-Sudhakar

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On Behalf Of Dimitri
> Papadimitriou
> Sent: Sunday, June 17, 2001 6:36 AM
> To: [email-masked]
> Cc: Yakov Rekhter; [email-masked]; [email-masked];
> [email-masked]
> Subject: Re: constraint-based routing algorithms
>
>
> Robert,
>