OSPF and the distance command

From: sabri_esame@yahoo.com
Date: Fri Aug 11 2006 - 18:44:18 ART

Hi all,
I'm trying to understand how ospf behaves in relation with the following command:

distance <#> <route-source> <wildcard> <acl>

I have the following topology:

 R1 --------
           |
           R3
           |
 R2 --------

R1, R2 and R3 are all in area 0. All routers have their loopbacks advertised in area0.

R1 and R2 are also ASBRs and can reach the same set of external networks.

I want to configure R3 in such a way it will forward all traffic for external networks to R2.
I know I can accomplish that modifying the redistribution metrics in R1 and R2, but as I said I'm trying to understand how the *distance* command behaves.

I thought I could solve the problem doing the following:

R3 

---

router ospf #
  distance 109 <R2 RID> 0.0.0.0 1

access-list 1 deny <R1's loopback>
access-list 1 permit any 

but it doesn't work.

All external routes are still load balanced between R1 and R2 and show up in the routing table with AD 110.
The only route with AD = 109 is R2's loopback. If I remove the acl from the distance command, i.e.

distance 109 <R2 RID> 0.0.0.0

also R1's loopback will be shown with distance 109 and R2 will be preferred (!!!). All other routes will still be load balanced and will have AD 110

Only if I shut the link between R1 and R3 I finally see these routes with an AD of 109.

I really don't understand what is going on, any ideas?

Thanks
Sabrina

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