How to stop the EX External routes from propagate the internal network

[byme88]

I have a network that runs 3 dynamic routing protocols:

BGP

OSPF

EIGRP

Redistribution:

BGP ----> OSPF------> EIGRP

Internal network runs EIGRP with default-routes to OSPF and BGP

Now, the internal network routing table shown many unwanted EIGRP EX routes.

Is there a way to stop this EX (External route) from propagate the internal network?

Can someone shed some light here?

Thanks,

byme88

[Jon Marshall]

Does the default route on the internal network come from OSPF ? 

The obvious answer if you do not want EIGRP external routes is don't redistribute OSPF into EIGRP but I suspect it may be more complicated than this ? 

Jon

[MHM Cisco World]

how BGP connect to EIGRP ??? is it chain redistribute from BGPintoOSPF and then OSPFintoEIGRP

[byme88]

Via a ASA Firewall 5525X

[byme88]

I forgot to mention that the default 0.0.0.0 route are also an EX route learned from the OSPF process

[Jon Marshall]

So use a route map when you redistribute into EIGRP and only allow the default route as that is all you need by the looks of it. 

Jon

[byme88]

This might work!  If I am not mistaking ASA does support route-map now. Thanks for the suggestion!

[byme88]

Hi Jon,

Can you please post an example of a route-map configuration for both the ASA and Router?

Much appreciated!

Byme88

[Jon Marshall]

ASA - 

https://www.cisco.com/c/en/us/td/docs/security/asa/asa94/config-guides/cli/general/asa-94-general-config/routes-maps.html#ID-2153-00000216

IOS - 

https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/49111-route-map-bestp.html#basics

Note I haven't done it on an ASA and have found that if you use "permit 0.0.0.0" as the default route it may or may not allow all routes so if that is the case instead of doing it on the ASA you could filter it on the internal router using a distribute list but it would be better to do it at the source if possible.

Jon

[MHM Cisco World]

distribute-list IN which use prefix-list to filter 0.0.0.0/0 come from BGP

[MHM Cisco World]

https://petri.com/how-to-use-a-distribute-list-to-filter-out-routing-updates-in-cisco-ios/

[Flavio Miranda]

Any reason for two differents IGPs? 

[byme88]

As far as I know, there must be some reason for the predecessor to use 2 IGPs, but it is already done and I am just trying to optimized (clean-up) the network full with EX routes. Thanks!

[Flavio Miranda]

Alright.  Then use filter with route-map and you´ll be fine.

[Flavio Miranda]

Hi

  The EX routes are routes advsertised from others routing protocol into EIGRP, so, it seems to me that they are expected on this case.

What you can do is create filters so that only routes you want will be redistributed into EIGRP.