[c-nsp] Cisco and BGP MED

[Harold Ritter (hritter)]

Hi Brandon,

See comments inline.



Le 2013-03-29 16:14, « Brandon Ewing » <nicotine at warningg.com> a écrit :

>Is there a knob in Cisco IOS to enable sending the MED learned from an
>iBGP
>peer to an eBGP peer?

No. You can't propagate a MED received via iBGP to an eBGP neighbor but
you could set the MED from the IGP metric to the BGP next-hop as follow:


router bgp x
 neighbor y.y.y.y remote y
 neighbor y.y.y.y route-map setMed
   
route-map setMed permit 10
set metric-type internal

>Currently, it appears that if an iBGP route is
>learned from a local network/aggregate statement, the MED is sent to an
>eBGP
>peer, but if the iBGP route is learned from an iBGP peer, no MED is set on
>the update to the eBGP peer.

HR> This is normal behaviour. If the MED is learnt over iBGP it will not
be sent to an eBGP neighbor.

> 
>
>Confirmed this in my 7206VXR lab, appears to be so in production on my
>Sup720s, but my Foundry MLX series appear to send the learned MED
>regardless.
>
>Lab output (Route sourced by netowrk statement on R21, advertised to R2 in
>same AS, who advertises it to R1 in different AS):
>
>R21#show ip bgp 192.168.40.0
>BGP routing table entry for 192.168.40.0/24, version 2
>Paths: (1 available, best #1, table Default-IP-Routing-Table)
>  Advertised to update-groups:
>        1
>  Local
>    0.0.0.0 from 0.0.0.0 (2.2.2.21)
>      Origin IGP, metric 10000, localpref 100, weight 32768, valid,
>sourced, local, best
>
>R2#show ip bgp 192.168.40.0
>BGP routing table entry for 192.168.40.0/24, version 2
>Paths: (1 available, best #1, table Default-IP-Routing-Table)
>  Advertised to update-groups:
>        2 
>  Local 
>    2.2.2.21 (metric 65) from 2.2.2.21 (2.2.2.21)
>      Origin IGP, metric 10000, localpref 100, valid, internal, best
>
>
>R1#show ip bgp 192.168.40.0
>BGP routing table entry for 192.168.40.0/24, version 3
>Paths: (1 available, best #1, table Default-IP-Routing-Table)
>  Not advertised to any peer
>  65002 
>    1.1.2.2 from 1.1.2.2 (2.2.2.2)
>      Origin IGP, localpref 100, valid, external, best
>
>-- 
>Brandon Ewing     
>(nicotine at warningg.com)