Re: [isp-bgp] Tier-2 reachability and multihoming

[Tom Vest <tvest@...>]

Hi Pavan,

Can you give us a few examples of networks that you believe are 
suffering this reachability problem?

Thanks,

Tom

Tom Vest
Research Program Manager
Packet Clearing House
http://www.pch.net

On Mar 21, 2005, at 12:49 AM, G Pavan Kumar wrote:

> Hi there,
>         I have been working on characterizing the internet hierarchy.
> I noticed that 27% of the total possible tier-2 provider node pairs 
> are not
> connected i.e., they dont have any tier-1 node connecting them nor a
> direct peering link between them.
>      Multihoming can be used as a predominant reason for the 
> reachability of tier-3 nodes which are customers of these nodes, but 
> what about the reachability of tier-2 nodes themselves and its 
> customers which cannot afford to multihoming? How does BGP solve this 
> reachability problem when it gets a request to a prefix unreachable?
>
>       1        tier-1
>     /
>   2      4     tier-2
>  / \    /  \ 5   6  7    8  tier-3
>
> here, nodes 2 and 4 have no reachability,
>       1
>     / |
>   2   3   4
>  / \   \/  5   6  7    8
>
> now, node 7 is reachable from 2 and its lower level nodes, but what 
> about node 4 and 8, and as a typical case, suppose nodes 4 and 8 have 
> no multihoming whatsoever, what then?
>
> Regards,
> pavan



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