Tier-2 reachability and multihoming

Thu Mar 24 04:58:28 UTC 2005

--On Wednesday, March 23, 2005 4:54 PM +0530 G Pavan Kumar 
<pavanji at 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.