12-01-2008 11:06 AM - edited 03-04-2019 12:33 AM
Hi
Looking at the BGP Cost Community, I keep reading about how this influences the BGP best path selection process at the point of insertion (POI). Does this mean that the decision is taken immediately after step 8 in the Best Path Algorithm - ie Prefer the path with the lowest IGP metric to the BGP next hop?
For some reason I cannot get my head round this POI stuff.
Thanks
12-01-2008 11:22 AM
Walter,
The POI indicates when, in the BGP best path selection process, the cost community is taken in consideration. There is only two choices for the value of the POI:
Router(config-route-map)#set extcommunity cost ?
<0-255> Community ID
igp Compare following IGP cost comparison
pre-bestpath Compare before all other steps in bestpath calculation
Router(config-route-map)#set extcommunity cost
So as you can see it can be either compared before everything else (pre-bestpath) or right after the IGP cost comparison (igp).
Regards
12-01-2008 12:01 PM
Great answer - Thanks very much!
10-21-2010 02:33 PM
When I look at the options for this command it appears to me that there are actually 3 different scenarios: I can select IGP, pre-bestpath or I can not specify the POI at all.
The question is, if I don't specify, which is chosen? The documentation leads me to believe that it would be IGP by default but the fact that there is a specific keyword for IGP makes me doubt myself.
Any thoughts?
Edit:
Nevermind, I figured this out the easy way, just try it. If you don't specify either option it does just default IGP and actually adds that keyword into the config.
IR0(config)#route-map test-cost-comm
IR0(config-route-map)#set extcommunity cost 1 100
IR0#show run | sec route-map test-cost-comm
route-map test-cost-comm permit 10
set extcommunity cost igp 1 100
IR0#show route-map test-cost-comm
route-map test-cost-comm, permit, sequence 10
Match clauses:
Set clauses:
extended community Cost:igp:1:100
Policy routing matches: 0 packets, 0 bytes
Message was edited by: Robin Martinez
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