[isp-bgp] Re: Multiple Peerings on the same link

[James <haesu@...>]

On Wed, Sep 08, 2004 at 12:58:56PM +0530, Tulip Rasputin wrote:
> Hi,
> 
> Any reason why somebody would want to have multiple BGP peerings/sessions 
> with the *same* router over the same link? I can understand, if its 
> multiple links (load balancing and redundancy), but why over the same link?
> 
> One possible reason that comes to my mind is: if one of the peers wants to 
> implement some sort of policies, so he accepts one feed over one session, 
> applies its policies and accepts the same feed over the other BGP session 
> and applies a different set of policies. I know, all of this can be done 
> with a single BGP session too, but this is the best that comes to my mind. 
> Has anyone in this list ever seen such a case, wherein we have multiple BGP 
> sessions between the same peers over the same link!

I've not seen a practical reason to do so over single hop peering 
for both sessions.

However, there are cases where people do run two sessions over a single
link. Popular being, one session being a single hop, other being a multihop.

Cogent still does this in several service regions. For buildings with L3
access switches that cannot hold full routes, you peer over single hop to
their access switch to advertise your routes to; then you peer with their
core router one hop above, via ebgp-multihop 2, to receive full routes.

HTH,
-J

--
James Jun                                            TowardEX Technologies, Inc.
Technical Lead                        Network Design, Consulting, IT Outsourcing
james@...                  Boston-based Colocation & Bandwidth Services
cell: 1(978)-394-2867           web: http://www.towardex.com , noc: www.twdx.net







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