Handling default routes in OSPF Normal Area

[koray.gurel]

In this topology, both Router233 and Router234 receive def route from other network via BGP

Those default routes are sent to R1.

R1 anonunces the def route received from one link to the other. Def rotue received from Router233 is sent to the other Router234 and vice versa

Is this something expected as all should have same routing DB?

Is there a known way to prevent R1 forwarding default routes? 

When Router233 receives the def route via BGP and meantime it receives another def route caused by Router234 via y.y.y.16/29 network (R1 forwards the received def route), it makes confusion where to route the packets.

Thanks,

Koray G.

[paul driver]

Hello

Are you redistributing everthing from ospf into bgp?  If you only redistribute connected and static networks then the default routes R1 is receiving shouldn't even get redistributed back into bgp.

Lastly the two defaults R1 receives from the BGP routers can be advertised with default route being preferred over the other and the easiest way to to that is by metric-types

Example:
D223 rtr
default-information originate metric-type 1 <-- preferred default

D224 rtr
default-information originate

[koray.gurel]

Hi Paul,
Thanks for your time.
No for the first question. Default route from OSPF is not forwarded to BGP. (what I know)

Actually I am looking into the situtation from R1 view. I cant control the other routers in this network.
In R1 perspective,
Isnt it very normal that I announce a def route received from Router223 to Router224 and a def router received from Router224 to Router223?
Is there any natural way not to forward a received default route to another link at R1 side? Does it help changing the ospf area to something else which might cause R1 not to announce those def routes to others?

[gaston.benitez]

Hi Koray.

Some questions.

Do you have IBGP between routers 233 and 234?

Routers 233 and 234 share the same AS number?

Sources from the default route comes from are from the same AS or from different ones?

Thanks

[koray.gurel]

Hi Gaston,

What I know there is an OSPF area between 233 and 234 and they should be in same AS with my gw.

Default routes are received from different sources and I belive they are in another AS. Unfortunatelly I cant reach to the details of those next hops.