Friday, 5 July 2013

Redistribution Between RIP and OSPF

Redistribution Between RIP and OSPF





  • Configure RIPv2
  • Configure OSPF
  • Allow One-way Redistribution
  • Redistribute Between Two Routing Protocols
  • Set a default seed metric
  • Modify OSPF external network types
  • Configure summary addresses

Configure RIP

We can check both the routing table and database to verify the configuration;

You can verify the routes coming in from RIP advertisements with the database command;

If can see that in R1 routing table its receiving advertisements from R2's interface. This is because R2 is advertising the entire class B network of You can see this with the following command;

To stop this behavior you disable RIP updates being sent out that interface. You can do this with the following command;

If you check the interface again now you will see interface s0/1 is no longer part of the RIP process.

The loopback interfaces will also participate in the RIP process as you can see if you issue the debug ip rip command;

You can do the following to put the loopbacks in passive. I will do this for both R1 and R2.

If we look at R2 routing table we can see that it has a number of routes to R1 loopbacks. We can use a summary address the cut down the routing table size.

As I am using RIP, Cisco IOS does not allow you to summarize to mask length that is less than the classful network prefix.

To get around this we can do the following;

We can see that the route has been added to R2s routing table;

On R1 I'm going to apply a prefix list so that only the summary route and loopback 0 and 70 are advertised to R2.

The prefix list will prevent the more specific routers to loopback 48 - 51 and allow everything else.

Like an ACL we need to apply it to the interface;

We can verify this on R2;

Configure OSPF

I'm just going to use a few show commands to verify everything is working;

Ok now i'm going to put the loopbacks in a passive state. This can be done using the following commands;

This will put all interfaces into passive I will need allow s0/1 to participate in OSPF.

 To verify this configuration you can use the following commnad;

Allow One-way Redistribution

 Right now I'm going to configure OSPF to redistribute into RIP. To do this I need to go on R2 and enter the redistribute command;

You can verify this with the sh ip protocols commands;

If we look at R1 routing table we can see that it has the OSPF routes, however R3 does not have a route back to R1. You can use a traceroute to check this.

To overcome this we can use the default-information originate always command. This will force R2 to advertise a default route in OSPF.

Redistribute Between Two Routing Protocols

You can substitute the default route with actual and more specific routes. First I'm going to remove the command I just entered and use the redistribute rip command on R2.

when we check the routing table on R3 the only external OSPF route that came in was the network.

This is because by default OSPF only accepts classful networks when redistributing into it. You can modify this behavior by adding the following commands;

We should now have full connectivity between all the networks;

Set a Default Seed Metric

A seed metric is used for redistribution, instead of or in addition to setting metrics on a per-protocol basis. Seed metric are used when redistributing into distance vector protocols. By using the follow command you can configure a default metric for redistributed routes on a per protocol basis.

Modify OSPF external network types

You can see from R3 routing table the O E2 routes which means OSPF external type 2. There are two external metric types, and E2 is the default. External type 1 metrics increase like a usual route, whereas external type 2 metrics do not increase as they get advertised through OSPF. 

You can change this by using the following commands;

If we know check the routing table on R3 we can see that the metric has changed;


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