Redistribute only /32 prefixes via BGP

[Tauer Drumond]

Hi all,

I have a simple topology, where R1 is connected to R2 with a BGP session between them.

On R1, I have a static route: 10.0.130.0 255.255.255.0 192.168.0.1

I just want send to R2 only prefixes 10.0.130.18/32 and 10.0.130.58/32, not all 10.0.130.0/24 network

Is there a way to accomplish that?

Thank you

[willwetherman]

Hi Tauer,

Yes, a simple way is to add static routes for the /32 networks in addition to the /24 and then advertise them into BGP using the network command.

For example:

ip route 10.0.130.0 255.255.255.0 192.168.0.1

ip route 10.0.130.18 255.255.255.255 192.168.0.1

ip route 10.0.130.58 255.255.255.255 192.168.0.1

router bgp 100

 network 10.0.130.18 mask 255.255.255.255

 network 10.0.130.58 mask 255.255.255.255

Hope that helps

[Yaron Golan]

Hi Tauer,

you can use the Null 0 Routes from the advertise router. 

and filter it by distribute list.

R1:

Static Routes:

ip route 10.0.130.18 255.255.255.255 null 0

ip route 10.0.130.58 255.255.255.255 null 0

ACL:

access-list 1 permit 10.0.130.18 0.0.0.0

access-list 1 permit 10.0.130.58 0.0.0.0

BGP:

router bgp 100

 network 10.0.130.18 mask 255.255.255.255

 network 10.0.130.58 mask 255.255.255.255

 network 10.0.130.0 mask 255.255.255.0

 neighbor R2 remote as x 

 neighbor R2 distribute-list 1 out

[Tauer Drumond]

Thanks for the answer, but sorry, I forgot to mention... in this scenario, I can't use static routes.

In fact, I receive the prefix 10.0.130.0/24 via a routing protocol.

I'd like to advertise only 10.0.130.18/32 and 10.0.130.58/32 to R2

Sorry to describe the wrong scenario

[Yaron Golan]

You have to see the problem like this: BGP will not advertise something (network) that doesn't exist in your routing table. You need to have a specific subnet in your routing table, before it can be advertised through BGP.

[Tauer Drumond]

Hi Yaron,

thanks for the answer.

Yes, I have this in mind... but I'm just trying to figure out if there's some workaround (wihtout using static routes)

I had no luck so far

[Philip D'Ath]

What about a different approach.  What you are describing to be is policy routing.

Why not just configure policy-routing on R2?