RIP into EIGRP Redistribution

[mohankumarm]

Hello,

In this scenario, i am trying to redistribute RIP into EIGRP on a core switch. The core switch runs both RIP and EIGRP protocols and RIP routes are received from an external router which is filtered off using distribute-list inbound. After redistribution of RIP into EIGRP( one way), i can see all the RIP routes are present in the EIGRP topology table, but the RIP routes are not present in the EIGRP routing  " sh ip route eigrp:" 

Thanks and Regards,

Mohan

[Peter Paluch · Accepted solution]

Hello Mohan,

If redistributing routes from RIP, these routes must stay RIP-learned on the router that performs the redistribution. The redistribute rip command in fact tells the EIGRP to search for RIP-learned routes in the routing table and inject them into EIGRP. If these routes changed to EIGRP-learned, the redistribute rip would no longer apply to them, causing them to be flushed from EIGRP's database immediately.

A key fact to remember when performing redistribution is that during redistribution, the routing table on the router performing the redistribution will not change. Source routes will stay the way they are - they won't be replaced by the destination routing protocol.

Does this make sense?

Best regards,

Peter

[mohankumarm]

Hi Peter,

thanks very much indeed and yes it is very clear now and i have observed the same while doing this redistribution and also just wondering what happens if there is a redist connected statement in the routing protocol configuratio..So for eg, redistribute rip into eigrp will do 1) " show ip route rip" and grabs all the rip rip routes and 2) it will pick up the connected routes that rip is advertising ...So question if i have an additional redist connected statement in eigrp, will it break the routing?

Thanks and Regards,

Mohan

[Peter Paluch · Accepted solution]

Hello Mohan,

So question if i have an additional redist connected statement in eigrp, will it break the routing?

No, it won't. In fact, the redistribute rip injects routes that are

• Either learned by RIP
  
• Or directly connected and included into RIP using the network command in the router rip section
  

In other words, redistribute rip configured in EIGRP will cause EIGRP to retake all routes that are either learned by RIP or directly connected and advertised by RIP.

Configuring redistribute connected will add all directly connected networks into EIGRP, regardless of whether they are added to any routing protocol. Sometimes people get sligthly confused what is the difference between using redistribute connected and a network command covering all directly connected networks. The main difference is that the redistribute connected command will only cause the directly connected networks to be injected and advertised in the routing protocol but the routing protocol will not run over these interfaces. A routing protocol communicates only over those interfaces added using the network command. An interesting consequence is that configuring a routing protocol with redistribute connected but without any network command will do nothing - as there is no interface added to the routing protocol over which the protocol can communicate, it remains silent.

You are welcome to ask further!

Best regards,

Peter

Best regards,

Peter

[mohankumarm]

Hi Paul,

Very Interesting indeed as i was thinking otherwise,thanks a lot for clearing this up..The current issue  is related to the following scenario.

We have core routers A and B (3750's L3) connected in a Layer2 Port channel running RIPv2 on the current existing network. On the new network are core routers C and D(65K's) connected in a p2p manner to A and B, i.e.                     Router A connected to C and Router B to D. Router C and D are interconnected by L3 Poirt channel and running EIGRP on the new network. Now, RIP is also implemented on the new network (C and D) and mutual redistribution of RIP/EIGRP with tagging feature is implemented on (Routers C and D only)to ensure prevention of routing loops.

The issue is as follows:

For the existing network there is a default route to the Internet pointing to the firewalls on the existing network.Likewise for the new network, there is a default route to the Internet from the firewalls on the new network.

After redistribution is performed, the default route on the existing network is reconfigured to point to the new core node next hops on each p2p link( On Ra 0.0.0.0 next hop C and on Rb 0.0.0.0 to next hop D). Now everything works fine, until one of the p2p links goes down. In this scenario, the EIGRP learned or RIP learned routes on both existing and new networks are fine, but the default route on the existing network is learnt from RIP ( the existing network protocol) and as expected, points to its next hop (A points to B), but B does not route to D..Is there any particular feature( null routing for instance) on the existing RIP network to be applied to ensure that the default gets forwarded from A to B and then to D in case of A to C failure and vice versa.

Thanks again.

Mohan

[Peter Paluch]

Hello Mohan,

I apologize for answering late.

I am afraid I have troubles understanding your problem in its entirety. You are saying that A points to C for default route, and B points to D (how is this accomplished - routes dynamically learned or configured statically?). Now, you are also saying that when the A/C link goes down, B no longer routes through D. Why would that be the case? As B did not use path through A, why would the A/C link failure influence B's routing table?

Best regards,

Peter