RE: OSPF and the distance command

From: Michael Stout (michaelgstout@hotmail.com)
Date: Fri Aug 11 2006 - 19:33:06 ART


I don't think you network is a good candidate for studying distannce.

try this
r1-----------r2---------r3------r4
r1----------r6---------r5-------r4
OSPF on top RIP on bottom>
redistriburte mutually using default rip metric of 1>
from r1 trace to R5 rip>
You trace will go r2--r3--r4--r5
that is because ospf has a better DISTANCE and r1 thinks the path to r5
is one hop away if it uses the ospf path but it thinks the path to R5 is
2 hops away if it takes the path through r6.
You need distance so you use the native protocol

Next ad loopbacks to R6 and R5.
You will not be able to trace to the loopbacks from the ospf network
You need to use distance to kill the loop

  --------------------------------------------------------------------

  From: sabri_esame@yahoo.com
  Reply-To: sabri_esame@yahoo.com
  To: ccielab@groupstudy.com
  Subject: OSPF and the distance command
  Date: Fri, 11 Aug 2006 17:50:07 -0400
  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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