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Re: BGP Confederation config problem...

  • From: Richard Parker
  • Date: Tue Mar 10 03:47:17 1998

Andy McConnell wrote:
>Avi Freedman suggested using a +1 metric when leaving each member-AS. 
>But it doesn't seem to help - perhaps I didn't do it right. 
>In fact, it doesn't look like the metrics are adjusted more than 1.  
>Setting the MED is the crux of the problem - I can set it "statically",
>but the idea is to make the whole confederation dynamic.  I want the
>confederation to work like a true "internet".  (Yes, I'm asking for the


Perhaps a solution, albeit an ugly solution, to the problem is to
use a large route-map that matches and increments the MED for the
expected range of MED values.  Each router would have a route-map
to increment the metric on updates that it sends.  On the Cisco
this configuration might look something like the following:

neighbor a.b.c.d route-map INC-MED out
route-map INC-MED permit 1
  match metric 0
  set metric 1
route-map INC-MED permit 2
  match metric 1
  set metric 2

If dorian's remark is true...

>This won't work because Cisco's bgp implementation skips over MED
>from neighboring sub ASes inside a confederation in its decision

...then instead use a route map to increment the local preference
for each route received.  You would still probably want to set the
MED from the local preference before you export routes so that the
external neighbors (in other ASes) of the confederation members
choose to send data into the confederation at the point closest to
the ultimate destination.