Re: 1-prefix, 1-AS question

[Curtis Villamizar <[e-mail]>]

In message <[e-mail]>et>, [e-mail].j
p writes:
> Hello,
>    I'm a newcomer to the world of BGP, though I have some experience
> with Internet routing.  My company is just now having to become its
> own AS and start handling routing to the outside world.
> 
> The situation is this: we have until now been connected through a
> single provider, P1, and have been included in their AS.  Now we're
> planning to connect to P2 and P3 as well.  Our IP addresses belong
> to P1's CIDR block.
> 
> I read in Hawkinson & Bates' Internet draft "Guidelines for creation,
> ... of an AS" that a prefix should ordinarily belong to only a single
> AS, but that it is not unacceptable to have it belong to multiple ASes.
> But I don't understand BGP well enough to see under what circumstances
> this may be allowed.
> 
> My question is:
> If we advertise our routes via BGP to P2 and P3, will this conflict
> with their implicit advertisement by P1 as part of P1's CIDR block?
> 
> If I've missed something in the literature, a pointer would be much
> appreciated. Thanks in advance,
> 
> Dave Iannucci                                     ATSON, Inc., Tokyo, Japan


You should advertise a prefix that is more specific than the CIDR
block from which it was provided.  The more specific route will
originate from exactly one AS, your.

In the future it may be possible to aggregate across provider
boundaries so that distant sites such as the US still see just an
aggregate pointing across the Pacific (or perhaps across the Asian
continent, in other cases).

Curtis