[c-nsp] bgp multipath-relax + dmzlink

[Oliver Boehmer (oboehmer)]

bill fumerola <> wrote on Wednesday, December 17, 2008 01:04:

> config:
>  bgp bestpath as-path multipath-relax
>  bgp dmzlink-bw
> 
>   neighbor aa.bb.cc.73 dmzlink-bw
>   neighbor xxx.yyy.zzz.77 dmzlink-bw
> 
> interface bandwidth settings:
> 
> rtr1#show ip route aa.bb.cc.73 | i direct
>   * directly connected, via GigabitEthernet0/0.5
> rtr1#show int gi0/0.5 | i BW
>   MTU 1500 bytes, BW 9000 Kbit, DLY 10 usec,
> rtr1#show ip route xxx.yyy.zzz.77 | i direc
>   * directly connected, via GigabitEthernet0/0.3
> rtr1#show int gi0/0.3 | i BW
>   MTU 1500 bytes, BW 55000 Kbit, DLY 10 usec,
> rtr1#
> 
> bgp shows the proper DMZ-link BW:
> 
> rtr1#show ip bgp 4.23.94.0
> [...]
>   2914 7018 46164
>     xxx.yyy.zzz.77 from xxx.yyy.zzz.77 (129.250.0.19)
>       Origin IGP, metric 0, localpref 100, weight 10000, valid,
>       external, multipath Community: 2914:420 2914:2000 2914:3000
>       36692:10210 no-export DMZ-Link Bw 6875 kbytes
>   701 7018 46164
>     aa.bb.cc.73 from aa.bb.cc.73 (137.39.2.70)
>       Origin IGP, metric 0, localpref 100, weight 10000, valid,
>       external, multipath, best Community: 36692:10210 no-export
>       DMZ-Link Bw 1125 kbytes
> 
> here's the problem:
> 
> rtr1#show ip route 4.23.94.0
> Routing entry for 4.23.94.0/23
>   Known via "bgp 36692", distance 20, metric 0
>   Tag 701, type external
>   Last update from aa.bb.cc.73 00:24:40 ago
>   Routing Descriptor Blocks:
>   * xxx.yyy.zzz.77, from xxx.yyy.zzz.77, 00:24:40 ago
>       Route metric is 0, traffic share count is 1
>       AS Hops 3
>       Route tag 701
>     aa.bb.cc.73, from aa.bb.cc.73, 00:24:40 ago
>       Route metric is 0, traffic share count is 10
>       AS Hops 3
>       Route tag 701
> 
> the traffic share count is the inverse of what it should be (1:10 when
> it should be 7:1).

looks like a bug, there have been a few, but not sure which one without
looking into this further. I don't think it's related to "bgp bestpath
as-path multipath-relax" in any way, rather a bug in how BGP calculates
the share count it passes to RIB..

Maybe CSCsg31316 (Changes in dmzlink-bw do not reflect in the routing
table) or CSCsg31406 (don't think so)..

	oli