What is multihoming was (design of a real routing v. endpoint id seperation)

Tue Oct 25 10:11:43 UTC 2005

On Mon, 24 Oct 2005 Michael.Dillon at 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