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Re: BGP Confederation config problem...

  • From: Andy McConnell
  • Date: Tue Mar 10 11:47:58 1998

:-)  I tried this already, but the match metric only works with IGRP
route-maps, not BGP :-)


Andy McConnell       アンディ マッコネル
Network Architect, NTT Multimedia Communications Laboratories

Calvin: People think it must be fun to be a super genius, but
they don't realize how hard it is to put up with all the idiots
in the world.
Hobbes: Isn't your pants' zipper supposed to be in the front?

On 10 Mar 1998, Richard Parker wrote:

richard_parker> Andy McConnell wrote:
richard_parker> >Avi Freedman suggested using a +1 metric when leaving each member-AS. 
richard_parker> >But it doesn't seem to help - perhaps I didn't do it right. 
richard_parker> >In fact, it doesn't look like the metrics are adjusted more than 1.  
richard_parker> >...
richard_parker> >Setting the MED is the crux of the problem - I can set it "statically",
richard_parker> >but the idea is to make the whole confederation dynamic.  I want the
richard_parker> >confederation to work like a true "internet".  (Yes, I'm asking for the
richard_parker> >world...)
richard_parker> Andy,
richard_parker> Perhaps a solution, albeit an ugly solution, to the problem is to
richard_parker> use a large route-map that matches and increments the MED for the
richard_parker> expected range of MED values.  Each router would have a route-map
richard_parker> to increment the metric on updates that it sends.  On the Cisco
richard_parker> this configuration might look something like the following:
richard_parker> neighbor a.b.c.d route-map INC-MED out
richard_parker> !
richard_parker> route-map INC-MED permit 1
richard_parker>   match metric 0
richard_parker>   set metric 1
richard_parker> route-map INC-MED permit 2
richard_parker>   match metric 1
richard_parker>   set metric 2
richard_parker> (etc.)
richard_parker> If dorian's remark is true...
richard_parker> >This won't work because Cisco's bgp implementation skips over MED
richard_parker> >from neighboring sub ASes inside a confederation in its decision
richard_parker> >process.
richard_parker> ...then instead use a route map to increment the local preference
richard_parker> for each route received.  You would still probably want to set the
richard_parker> MED from the local preference before you export routes so that the
richard_parker> external neighbors (in other ASes) of the confederation members
richard_parker> choose to send data into the confederation at the point closest to
richard_parker> the ultimate destination.
richard_parker> -Richard