BGP anuncia rutas más específicas dentro de un VRF

[jnmedina]

Hola,

We need to advertise via BGP more specific subnets to balance the traffic via two circuits. In order to add those subnets to the BGP table, we need to add them first to the ip routing table, we tried using statics routes pointing to null0 but in this way the traffic get discarded, as it can be used just for summarising subnets and not the opposite (doing the subnets smaller)

Command used:

ip route vrf voicevrf 192.168.1.45 255.255.255.255 null0

We were investigating other ways to do that and for the global routing table it is possible to point the static route to exit LAN

interface, in this way:

Router(config)#ip route 192.168.1.45 255.255.255.255 Gi0/0/1.200

But for a vrf is not possible, and we get the following message:

Router(config)#ip route vrf voicevrf 192.168.1.45 255.255.255.255 Gi0/0/1.200
% For VPN or topology routes, must specify a next hop IP address if not a point-to-point interface

I can not point to an IP next-hop, as the router is connected to a L2 switch, where the servers are connected. 

What will be the best aproach to solve this? is there any way to do it?

Thank you in advance 

PD: in this post Solved: BGP Announcing more specific routes (/23 in two /24) - Cisco Community it was solved using the LAN interface as next-hop but for a vrf seems that its not possible.

[Julio E. Moisa]

Hi

You could do that through 2 ways, I dont know about your real scenario but try with:

1- Using loopback under VRF instead using static routes, it will let you have a real entry into the routing table and be able to publish via BGP

2- You can try using ADVERTISE MAPs , basically it will advertise some prefix if a condition is true.

I assume you are using Address Family VRF under your BGP AS.

Hope it works, Please let me know once it is tested and if you need more assistance.

Regards

[Hilda Arteaga]

Thanks for your assistance on this query @Julio E. Moisa 

[jnmedina]

Thank you @Julio E. Moisa 

We can not use loopbacks because the IPs that we want to advertise are already /32 host prefixes and I can not duplicate the IP addresses.

We are going to simulate a similar scenario using advertise-maps, before to try in production.

I think it can work.  

I will keep you posted

Thank you!

[Julio E. Moisa]

Thank you let me know if you need any assistance, other way could be using AS Access list with regular expresions to advertise prefixes generated by specific AS. it could be an alternative but it can be tested later.

Regards. 

[jnmedina]

Hello @Julio E. Moisa 

Sorry that I took so long to reply.

I was emulating my scenario with the advertise-maps but It did not work.

My real problem is that I dont have the /32 prefix in my routing table so it is not adding them to the BGP table. I dont know if there is a way to add the prefix to the BGP table even though I dont have them in the routing table, I was looking for that but I didnt find a way to do it.

As I explained before I can not add the prefix to the routing table because I dont have a "Next-hop" IP to configure in the static route (My router running BGP is connected to a L2 switch), and I can not configure the exit interface because I am using a VRF and Cisco doesnt allow it, here is the output when I use the static route with a exit interface:

Router(config)#ip route vrf voicevrf 192.168.1.45 255.255.255.255 Gi0/0/1.200
% For VPN or topology routes, must specify a next hop IP address if not a point-to-point interface

 Thank you

Regards