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Re: What is multihoming was (design of a real routing v. endpointid seperation)

  • From: Pekka Savola
  • Date: Tue Oct 25 06:13:07 2005

On Mon, 24 Oct 2005 [email protected] wrote:
A single tier-2 ISP who uses BGP multihoming with several
tier 1 ISPs can provide "multihoming" to it's customers
without BGP. For instance, if this tier-2 has two PoPs
in a city and peering links exist at both PoPs and they
sell a resilient access service where the customer has
two links, one to each PoP, then it is possible to route
around many failures. This is probably sufficient for most
people and if the tier-2 provider takes this service seriously
they can engineer things to make total network collapse exteremely

From RFC 3582, this is not multihoming (see the defs below). The above
is referred to as "multi-connecting" or multi-attaching (also see RFC 4116).

I agree, this is sufficient for many sites. Especially in academic world, many universities are just multi-connected, trusting the stability of their NREN's backbone and transit providers. Lots of commercial sites do it too, but some are wary due to events like L3/Cogent, L3 backbone downtime, etc.


A "multihomed" site is one with more than one transit provider.
"Site-multihoming" is the practice of arranging a site to be


A "transit provider" operates a site that directly provides
connectivity to the Internet to one or more external sites. The
connectivity provided extends beyond the transit provider's own site.
A transit provider's site is directly connected to the sites for
which it provides transit.

Pekka Savola "You each name yourselves king, yet the
Netcore Oy kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings