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 world...)
Andy, 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 (etc.) 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 process.
...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. -Richard
:-) I tried this already, but the match metric only works with IGRP route-maps, not BGP :-) -Andy -- 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> richard_parker> Andy, richard_parker> 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> 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> richard_parker> If dorian's remark is true... richard_parker> 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> 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_parker> -Richard richard_parker>
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