Conditional default route advertisement in rip

[rahul.nayar]

I am having one question regarding conditional default route advertisement in rip.

    My SETUP

=============

    10.10.10.0/24     20.20.20.0/24

R1----------------------R-----------------------R2

Router R routing table

C 10.10.10.0/24        0.0.0.0                    
C 20.20.20.0/24        0.0.0.0              

R1(config)#ip prefix-list test permit 10.10.10.0/24

R1(config)#route-map test

R1(config-route-map)#match ip address prefix-list test

R1(config-route-map)#exit

R1(config)#router rip

R1(config-router)#default-information originate route-map test

Question 1:

As my prefix-list matches the one in routing table. Should router R advertise to default-toute to R1 and R2 or only R1 ?

Question 2:

Should it matches only rip routes in routing table or any routes ( connected,loopback,ospf,bgp) ? If it matches any routes in routing table than what is the exact use of this behavior.

I have done testing in couple of releases but got different behavior so thought to ask experts regarding the exact behavior.

Regards,

Rahul N

[cadet alain · Accepted solution]

Hi,

It should advertise the default route to both routers.

It will match the prefix in the RIB wheter it is connected or learned by any other routing protocol.

Regards

Alain

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[blau grana · Accepted solution]

Hello,

Just to add to Alain comment -> by configuring set interface in route-map you can control on which interface route will be advertised.

Best Regards

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[rahul.nayar]

Hi Blau,

Thank you for an update.

I am also looking for a breif explanation of this feature.

Regards,

Rahul N

[blau grana]

http://www.my-ccie.com/2011/08/21/ccie-rs/conditional-default-advertisement-based-on-two-routes/

Best Regards

Please rate all helpful posts and close solved questions

[rahul.nayar]

Hi Cadet,

Thanks a lot for the kind update.

Could you also brief the exact use of this feature? Is it because the router is gateway for others ?

Regards,

Rahul N

[blau grana]

Hello Rahul,

It is used to advertise particular prefix only under some circumstances.

Lets say that you you have two Edge routers which run BGP with different ISP. You receive only default routes from both ISP. You want advertise these default routes to your LAN (via RIP/OSPF/EIGRP) only if BGP session is UP and you receiving default routes.

If you always advertise default routes from both Edge routers to your LAN, it could happen that one ISP link will fail, but because default route is still advertised from edge router (router has no default route to internet, BGP session is down) all traffic which will be routed toward particular Edge router will be blackholed or maybe routing loop could occur in case Edge router will learn default route via other Ege router.

Best Regards

Please rate all helpful posts and close solved questions