Re: 1-prefix, 1-AS question

[Paul Traina <[e-mail]>]

  From: [e-mail]
  Subject: 1-prefix, 1-AS question
  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?

No, however, unless P1 also explicitly transmits your longer routes, by
default, everyone will use P2 and P3 because your more specific information
takes precedence over P1's aggregate block (this is called longest match
routing).
  
  If I've missed something in the literature, a pointer would be much
  appreciated. Thanks in advance,

No problem, feel free to ask.
  
  
  Dave Iannucci                                     ATSON, Inc., Tokyo, Japan