North American Network Operators Group
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Re: Tier-2 reachability and multihoming

  • From: Michael Loftis
  • Date: Wed Mar 23 23:57:40 2005



--On Wednesday, March 23, 2005 4:54 PM +0530 G Pavan Kumar <pavanji@cse.iitb.ac.in> 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?
I think that likely you're looking at partial data (well i am sure you are, since i'm part of the internet and you didn't' get routing data from me...) and not seeing paths because of that. The BGP tables of a single node list all outward paths to other places. Thus from a single sample point it is totally impossible to 'map' the internet.

Not to mention the *constant* change in routing.