[nsp] Methods for Non-BGP multihoming

Daniel Golding dgolding@sockeye.com
Wed, 31 Jul 2002 14:05:49 -0400

RFC 1771 does indeed specify that inconsistant origin AS is an error state.


>> BGP relies on AS-path length if all other things are equal - there's
> no mention in the specification that origin ASes should be consistent nor
> that routers should throw away such advertisments. Arguably, any
> implementation that does is "broken".
> > To get back to the subject, non-BGP multihoming through provider-
> > specific space and NAT has been successfully deployed for years,*
> > without relying on spec ambiguities or any vendors' implementations
> > (or bugs). As such you can expect it to continure to work without
> > requiring a fire drill down the road.
> >
> > * yes, yes NAT is not a universal solution. But it works well for many
> >   leaf-node applications and if you're trying to avoid p;roper
> >   multihoming, leaf-node is probably a good description.
> I agree - for most situations, NAT is your friend. Particularly, if you
> need less than a /20 of IP address space many ISPs won't listen to you
> advertisments anyway. Unfortunatly, it's only effective if you only have
> clients using the 'net, not servers, but it should be the first choice for
> such situations.

Almost every ISP will listen to less than a /20 announcement from a
customer. A few won't listed to less than a /20 from PEERs.

> --
>          Ryan O'Connell - CCIE #8174
> <ryan@complicity.co.uk> - http://www.complicity.co.uk

- Daniel Golding