Redistribution from EIGRP/OSPF to BGP

[MOHAMMED SALMAN]

Hi All,

I have a topology and testing all possible routing in it. I am currently stuck in a redistribution scenario explained as below:

The Blue side is EIGRP and the Yellow side is OSPF. Both these protocol are running in a single AS. 

Now I want all these routes to be advertised to the BGP which is in Pink. However, I want to advertise a single summarized route and not individual route.

All 3 ASBRs are also running BGP.

[Julio E. Moisa · Accepted solution]

Hi

If the routers (with the arrows) are running IGP (I mean EIGRP or OSPF independently) and BGP redistribution could be not needed. You can use network,  route-map or prefix-lists to advertise or aggregate-address (with the summary-only argument) to the BGP peers. 

BGP will advertise the prefixes once they are into the routing table. 

Example:

router eigrp 100
network 172.16.0.2 0.0.0.0
!
router bgp 100
bgp log-neighbor-changes
network 10.0.0.0 mask 255.255.255.0
network 10.0.1.0 mask 255.255.255.0
network 10.0.2.0 mask 255.255.255.0
network 10.0.3.0 mask 255.255.255.0
aggregate-address 10.0.0.0 255.255.252.0 summary-only
neighbor 20.0.0.1 remote-as 101

The networks 10.0.X.0/24 are learned via EIGRP and included into the routing table, so you can advertise them to the BGP peers.

The BGP peer with IP 20.0.0.1 will receive a summary address only (attachment), if summary-only is not included it will advertise the summarized address + each prefix used to create the summarized network. So redistribution is not required. Also you can set up a metric to the aggregate address using route-maps so it will help you to prefer a path over other.

Hope it is useful

:-)

[MOHAMMED SALMAN]

Julio,

Ah!!! That would work :) however this would need all the networks to be advertised on the BGP process and then aggregate them.

Alternatively, I got a simpler workaround which however does not answer my own question :P. 

I made a static route and pointed it to null0 then redistributed that in BGP.

[cofee]

Like Julio stated you would only aggregate addresses that you want to advertise in BGP. You will just need to summarize the networks towards the BGP router and once you have those routes in the RIB of BGP speaker you can advertise them. No redistribution is needed.

[MOHAMMED SALMAN]

My previous comment helped me with redistribution of the summary route BGP.

Now I have another problem :( I wanted to redistribute the default route to into all the EIGRP/OSPF routers from the ASBR and to do this I did a redistribute of static. This redistribution also lead to advertise the null0 one.

I want the default route to be redistributed but not the null0 to the EIGRP/OSPF  peers from ASBRs 

[cofee · Accepted solution]

You can use route-maps to filter static routes you don't want to advertise or vice versa.

[Julio E. Moisa]

Hi

To be honest I dont like to use static route with null0, important traffic could be discarded. now if you are going to advertise a default route from an ASBR Router you could create a default route and configure under OSPF process: default-information originate command. This command will inject a default route through OSPF, if you have a mutual redistribution between OSPF and EIGRP, EIGRP will receive the default route like external EIGRP route. 

[MOHAMMED SALMAN]

Awesome!!! :D Thanks