Re: Confussion over multi-homing

[<dan () netrail net>]

Of course, peering agreements may speak to route filtering at that
particular interface, but can't assure global routability. For all intents
and purposes, /24s are globally routable, but their are several meaningful
exceptions - Verio and legacy class B space come to mind. 

Daniel Golding
Director of R&D    "I'm not evil. I'm just drawn that way"
NetRail, Inc.              
1-888-NetRail

On Thu, 14 Sep 2000, Brantley Jones wrote:

> At 01:23 PM 9/14/2000 -0500, you wrote:
>
> > Wouldn't one of the ISPs have to advertise a longer prefix?   I would think
> > that the address space would come from only one of the providers, in which
> > case the other provider would have to advertise this space on top of its own
> > /20.  It is irrelevant whether the two ISPs advertise one another, the
> > longer prefix would be the first choice for the backbone traffic.  If the
> > longer prefix route goes down, traffic would still go to the /20 the other
> > provider is advertising.
> > The ISP who is advertising the route on top of its own /20 can't aggregate
> > said route as it only can route to that portion of the address space defined
> > in the longer prefix.
> >
> > Geoff Zinderdine
>
> The problem is GETTING a /20 from anybody.  We recently tried and could 
> only get a /23 (being a small start-up).  BUT, that /23 is (apparently) 
> globally routable because of peering agreements with L3 and UUNET.  Our /23 
> prefix has yet to be filtered by anybody.
>
> Brantley