Mutual reDistribution

In a situation where you need to mutually redistribute between EIGRP and OSPF in 2 routers for example, where there will be no redistribute routes (170) on EIGRP's end, is it still necessarily to tag route on 1 router and deny those routes on the other routers?  From what I understand, there will be no HIGHER ---> LOWER problem.  Thanks.

Comments

  • Your understanding is correct.

    If there is no external route in EIGRP domain, route tagging is not necessary since the AD value will prevent the loop. 

    If any route that is redistributed from EIGRP to OSPF tried to get back into EIGRP domain, 110>90 is checked & loop is prevented. Likewise, the redistributed routes from OSPF to EIGRP can't get back into the OSPF domain becasue of 170>110.

    Hope this helps!

  • JoeMJoeM ✭✭✭

    Hi HeavyD,

    If I am reading this correctly, I think you are saying that there are only two routing domains (with no external routes).

    First draw a redistribution map:

            (eigrp)90/170 <--> 110/110(ospf)

    90 --> 110 external (will not go back into eigrp, as the original 90 is better than 110)

    110 --> 170 external (will not go back into ospf, as the original 110 is better than 170)

    answer:  no manipulation needed.  AD's handle the scenario.

     

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

    http://blog.ine.com/2008/02/09/understanding-redistribution-part-i/

    http://blog.ine.com/2008/02/19/understanding-redistribution-part-ii/

    http://blog.ine.com/2008/03/17/understanding-redistribution-part-iii/

  • JoeMJoeM ✭✭✭

    delete.

    double-posted for some reason.

  • JoeMJoeM ✭✭✭

    Hi HeavyD,

    If I am reading this correctly, I think you are saying that there are only two routing domains (with no external routes).

    First draw a redistribution map:

            (eigrp)90/170 <--> 110/110(ospf)

    90 --> 110 external (will not go back into eigrp, as the original 90 is better 119)

    110 --> 170 external (will not go back into ospf, as the original 110 is better than 170)

    answer:  no manipulation needed.  AD's handle the scenario.

     

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

    http://blog.ine.com/2008/02/09/understanding-redistribution-part-i/

    http://blog.ine.com/2008/02/19/understanding-redistribution-part-ii/

    http://blog.ine.com/2008/03/17/understanding-redistribution-part-iii/

  • In Volumn II Lab 11 task 2.2, there is only one redistributed prefix (R6's Loopback) in EIGRP and the distance command in both R3 and R5's OSPF process take care of that.  I was able to get full reachability without doing any route tagging and deny.  But looking at the solution, it has the route tag and deny configured in both R3 and R5's route maps. So I was just wondering if I am missing something here.

  • JoeMJoeM ✭✭✭

     Ahhhh. Then you do have a 170 route being redistributed in OSPF. That is different. ;-)

     Same thing.  draw the redistribution map, and look at the scenarios.  Now we have...

               170 --> 110    (bad, but solved by external AD change)

     

    The solution gives an explanation why the route tagging is done.   Routing Convergence time.

    In order to prevent any temporary loops from occurring during routing convergence,routes are tagged when re-distributed both from EIGRP into OSPF and from OSPF into EIGRP.

     

    Routing Convergence time is an interesting lesson (debated).   I believe there is a long thread under the sub-forum for this task. I will need to look for it.

Sign In or Register to comment.