XR-OS 4.2.0 bgp distance per neighbor?

[Dreggel001]

Hi,

We have recently migrated from 7600 to a ASR9010 with xr-os 4.2.0 and in the 7600 we had two different ibgp peers where we set an administrative distance for all traffic from one of those ibgp peers to 10, to make those routes more disareable than OSPF.

In the 7600 this command was "global" (not per neighbor) in the router bgp configuration, but with the possibility to specify the neighbor.

In the ASR9010 the command is still global but now changed so you can only specify administrative distance for all external, internal and local routes, with no possibility to specify neighbor. If we set internal routes to 10 it will also affect the other ibgp peer and that is not an option in my case.

Also, as far as I can see, there is no way to change administrative distance in a route-policy.

Have I missed something completely or has Cisco succesfully blocked the feature of setting administrative distance on a bgp route per neighbor? 

Best Regards

Johny              

[Alexei Kiritchenko]

Hello Johny,

You are correct, the admin distance is per protocol not per neighbor. May you show me your original 7600 config?

As of a workaround I may guess of splitting BGP network compare to OSPF. For example splitting BGP /24 route in 2 /25's would make them more specific then the OSPF route and hence more preferable.

Regards,

/A

[Dreggel001]

Here is our basic configuration of the 7600:

router bgp XXXX

no synchronization

bgp log-neighbor-changes

bgp dampening

network f.f.f.f mask 255.255.240.0

network n.n.n.n mask 255.255.248.0

neighbor x.x.x.x remote-as XXXX

neighbor x.x.x.x description ibgp_peer_1

neighbor x.x.x.x update-source Loopback0

neighbor x.x.x.x version 4

neighbor x.x.x.x route-reflector-client

neighbor y.y.y.y remote-as XXXX

neighbor y.y.y.y description ibgp_peer_2

neighbor y.y.y.y update-source Loopback0

neighbor y.y.y.y version 4

neighbor z.z.z.z remote-as YYYY

neighbor z.z.z.z description ebgp_peer_1

neighbor z.z.z.z ebgp-multihop 255

neighbor z.z.z.z version 4

neighbor z.z.z.z send-community

neighbor z.z.z.z soft-reconfiguration inbound

distance 50 x.x.x.x 0.0.0.0

no auto-summary

By setting distance to 50 on all routes coming from peer x.x.x.x those routes gets prefered over the same routes coming in from OSPF. Works like a charm.

In the ASR9K we can only set distance for external, internal and local routes. In the case above that would force routes coming in from the y.y.y.y peer to distance 50 aswell, and that could potentially be worse than bad.

Any idea if it is intentional to remove this "feature" in the ASR or if we could expect it to come back in a future soft?

/Johny

[Alexei Kiritchenko]

Hello Johny,

Correct, this “distance 50 x.x.x.x 0.0.0.0” is not supported on XR. There are no plans to have it. In general, that is considered a risky operation playing with bgp admin distance and not recommended to use.

Regards,

/A

[BTP3]

As another alternative, you could also use a route-policy and match on any routes from that neighbor and set the administrative distance in the route-policy. Then you could apply that route-policy to the neighbor in your BGP configuration.