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Re: BGP and aggregation

  • From: Richard A Steenbergen
  • Date: Sat May 11 17:56:54 2002

On Sat, May 11, 2002 at 05:34:39PM -0400, Ralph Doncaster wrote:
> I have transit in 2 cities.  I have a circuit connecting the 2 cities as
> well.  So far I've been using non-contiguous IPs, so there's been no
> opportunity for aggregation.  Having just received my /20 from ARIN, I'm
> trying to plan my network.  Lets say I split the /20 into 2 /21's, one for
> each city.  I'd like to announce the aggregate /20 instead of 2 /21's, as
> long as the circuit connecting the 2 cities is working.  If the circuit
> goes down I want each city to announce the local /21.  Is this
> possible? (using either a Cisco router or Zebra)

If I was paying for transit, I would want THEM to do the work of 
delivering it to the right city, without wasting the bandwidth of my 
circuit (unless they're really close and that circuit is really cheap).

If you're using the same transit provider in both cities, how about
announcing the /20, and the 2 /21s tagged with no-export. The /20 would be
heard by the world and get the traffic to your transit provider, then the
/21s would route it to the right exit point.

Richard A Steenbergen <>
PGP Key ID: 0x138EA177  (67 29 D7 BC E8 18 3E DA  B2 46 B3 D8 14 36 FE B6)

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