[78837] in North American Network Operators' Group
Tier-2 reachability and multihoming
daemon@ATHENA.MIT.EDU (G Pavan Kumar)
Wed Mar 23 23:15:57 2005
X-Antivirus-cse.iitb.ac.in-Mail-From: pavanji@cse.iitb.ac.in via jeeves.cse.iitb.ac.in
Date: Thu, 24 Mar 2005 09:45:05 +0530 (IST)
From: G Pavan Kumar <pavanji@cse.iitb.ac.in>
To: Nanog Mailing list <nanog@merit.edu>,
Cisco Mailing List <cisco-nsp-request@puck.nether.net>
Errors-To: owner-nanog@merit.edu
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
unreachable 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
