[78840] in North American Network Operators' Group
Re: Tier-2 reachability and multihoming
daemon@ATHENA.MIT.EDU (Michael Loftis)
Wed Mar 23 23:57:06 2005
Date: Wed, 23 Mar 2005 21:58:28 -0700
From: Michael Loftis <mloftis@wgops.com>
To: G Pavan Kumar <pavanji@cse.iitb.ac.in>, nanog@merit.edu
In-Reply-To: <Pine.LNX.4.61.0503231652450.6879@mars.cse.iitb.ac.in>
X-MailScanner-From: mloftis@wgops.com
Errors-To: owner-nanog@merit.edu
--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.
