On Mon, 24 Oct 2005 Michael.Dillon@btradianz.com 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 unlikely.
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 multihomed. and: 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