Re: [Idr] draft on virtual aggregation

Robert Raszuk <> Thu, 17 July 2008 19:08 UTC

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Date: Thu, 17 Jul 2008 12:07:41 -0700
From: Robert Raszuk <>
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Subject: Re: [Idr] draft on virtual aggregation
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>> This is not a hack. In fact all what this is about can be accomplished
>> today by sitting down and configuring three routers: edge, lookup
>> router and egress (an option). 
> Are you saying here that no router modifications are needed to make this
> work ?

To make this work in the simplest form what is required is:

*A* Ability to attract traffic to lookup routers (Done)

*B* Ability to label switch to lookup router (Done)

*C* Ability to prevent sending what is in the RIB to FIB if not needed 
(This is vendor dependent anyway - does not require any standard work)

*D* Ability to forward traffic to external peer without lookup on the 
edge ASBR (This is also quite implementation dependent but with PHP and 
embedded service label this could be accomplished)

>> If someone really want to divide the addressing
>> space as Paul suggest marking can be reg community. This is provider
>> contained solution - it does not cross any inter-as boundaries.
> I'm not sure what you mean by "marking can be reg community".  Can you expand
> a bit?

The community marking is needed only in the case of address space 
segmentation per lookup router in order for edge routers to recognize 
which out of the prefixes they receive should end up in FIB and which 
would only go as far as global RIB.

Such marking should be possible with standard community.

>> All this document attempts to is present such option for operators.
>> Some may find them useful some may not.
> I'm concerned that the folks that may find them useful (lower-tier ISPs)
> aren't typically involved in IDR or IETF for that matter.  If there are folks
> listening who can speak for lower-tier ISPs, please do so.  (My knowledge
> here, such as it is, is all second- or third-hand.)

I agree that IETF is not the best forum for that :). Much better would 

> For all of this fast restoration stuff, I gather you are thinking in terms of
> the core-edge structure that most (all?) tier-1 ISPs have?  Is your point
> that simply shrinking the number of routers that have to participate in
> re-routing will help scale ASBR/PE failure detection, and that we don't need
> explicit new mechanisms along these lines (i.e. BGP Virtual Link Attribute)?

Exactly. It helps scaling fast failure detection but what is more 
important it limits number of nodes where the redundant BGP paths must 
be present both in RIB and FIB.


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