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IOS XR extcommunity-set cost igp vs pre-bestpath

HI there,

I want to change the extcommunity cost pre-bestpath cost that is comming from a EIGRP route when received in BGP so that an eBGP path is preferred over the vpnv4 bgp path.  I have IOS XR and I am not sure if I can just adjust the pre-bestpath parameter or if I should change the igp poi as well.

 

I read the following post:

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).

 

So I think pre-bestpath is enough.  Can you please confirm?

 

 

This is what I am thinking:

prefix-set VRF_AAA-EIGRP-TEST
 10.10.17.4/32
end-set
!
extcommunity-set cost NEW-EXTCOMM-COST
 Pre-Bestpath:0:1500
end-set

route-policy VRF_AAA-TO-BGP-IN-TEST
  if destination in VRF_AAA-EIGRP-TEST then
    set extcommunity cost NEW-EXTCOMM-COST
  endif
end-policy

 

With this Policy, will COST:128:129:2842 look as COST:0:1500??  or should I change the IGP in the extcommunity-set ?  If so, how?

 

ASR_ROUTER#sh bgp vrf VRF_AAA 10.10.17.4
Tue Aug 29 20:43:27.110 CEST
BGP routing table entry for 10.10.17.4/29, Route Distinguisher: 217.10.16.20:20017
Versions:
  Process           bRIB/RIB  SendTblVer
  Speaker            2352257     2352257
Last Modified: Jul 11 06:36:43.715 for 1y07w
Paths: (1 available, best #1)
  Not advertised to any peer
  Path #1: Received by speaker 0
  Not advertised to any peer
  Local, (received & used)
    192.168.10.1 (metric 30) from 217.10.16.41 (192.168.10.1)
      Received Label 21665
      Origin incomplete, metric 2842, localpref 500, valid, internal, best, group-best, import-candidate, imported
      Received Path ID 0, Local Path ID 1, version 2352257
      Extended community: COST:128:129:2842 EIGRP route-info:0x0:1214 EIGRP AD:25384:538 EIGRP RHB:255:2:2304 EIGRP LM:0xff:1:1500 EIGRP AR:25384:85.89.249.7 EIGRP PM:9:0 RT:25384:20017
      Originator: 192.168.10.1, Cluster list: 217.10.16.41
      Source AFI: VPNv4 Unicast, Source VRF: default, Source Route Distinguisher: 192.168.10.1:20017

 

Thanks in advance!

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