North American Network Operators Group

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RE: Policy Routing

  • From: jlewis
  • Date: Sun Aug 26 02:32:01 2001

On Sun, 26 Aug 2001, Przemyslaw Karwasiecki wrote:

> Unless I am misunderstand how BGP (and routing at all)
> works something very seriously wrong with your suggestion.

Yeah...I should have put a few more seconds thought into that reply :)

> Your border router will advertise to a customer only best
> and active routes. You cannot advertise to BGP peer two routes
> to the same destination. So modifying AS_PATH will not work,
> because you will send to Customer X only best selected route
> from your border router.

This would basically tell the customer "don't send us traffic" since
assuming the cheapest path isn't the best path, the majority of routes
you send the customer would be non-cheapest peer paths with lots of

Just doing simple policy routing based on the customer's source address to
a next-hop of the cheap peer could cause all sorts of problems as well.
What if the cheap peer doesn't even have routes to the destination?  i.e.
the C&W/PSI peering issue a few months ago.  Say C&W is your cheap peer
and you send customer-X traffic to C&W desined for PSI.  C&W can't deliver
it and just drops it.  Sucks to be customer-X.

It looks like this problem is much easier to solve for incoming traffic
than for outgoing.

 Jon Lewis *[email protected]*|  I route
 System Administrator        |  therefore you are
 Atlantic Net                |
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