7 Replies Latest reply: May 11, 2012 11:00 AM by C1SC0M - CCNP,CWNA,Net+ RSS

    Eigrp, OSPF summarization dilemma


      I'm stuck on two issues and they involve summarization at the ASBR. I've attached a picture of the topology. If anyone can help me out and explain wha I did wrong and what I should have done that would be brilliant.Thanks


      I summarized the 4 networks belonging R4 into AND

      then issued the summary-address command on R3 into the OSPF

      process.R1 and R2 BOTH learned the as external

      routes. However for some strange reason R4 and R5 have also learnt

      the route and have learnt it externally via EIGRP.


      Conversely i have a similar problem when i summarized the loopbacks on R2

      into AND used the ip summary-address command on interfaces

      fa1/0 and fa0/1. r4 and r5 learn the summary which is great! but when i checked

      R2 i saw this:

      C is directly connected, Loopback2

      C is directly connected, Loopback0

      O E1 [110/201] via, 00:06:05, FastEthernet0/1

      C is directly connected, Loopback1

  is subnetted, 1 subnets


      Why is R2 receiving as an external route? I issued the ip summary-address command into the connected interfaces belonging to R3 which go into EIGRP.

        • 1. Re: Eigrp, OSPF summarization dilemma

          put the summary on R4 f0/0 towards R3.  R3 should then have the EIGRP routes


 from R4

 from R5


          you will advertise this into OSPF on R3.  Don't forget the subnets keyword as this is not a classful summary.


          since the OSPF area is only area 0, you don't have an ABR.  you have an ASBR in R3.


          redistribute the OSPF routes into EIGRP on R3.  Then on R3, put the summarry only on f0/1 towards R4 and f1/0 towards R5.


          you will need to use a route map for both the redistribute commands to filter the original routes back into their original domain.




          • 2. Re: Eigrp, OSPF summarization dilemma

            HI Brian, thanks a lot for your help. I think I got it working now. Well it did resolve it but i hope the syntax was OK. I summarized the on R4 as you suggested.


            I then used a prefix list and distribute list on R3 just to see if that would work and it did.


            R3(config)#ip prefix-list NETWORK-2 deny

            R3(config)#ip prefix-list NETWORK-2 permit le 32

            THIS got rid of the external route to in R1 and R2's routing table and also there won't be any external type

            5 LSAs for this network


            Alternatively I also used a route map and linked it to a Access-list. Issued on R3

                10 deny, wildcard bits (1 match)

                20 permit any (4 matches)

            Then create a route map on R3:

            route-map EIGRP>OSPF, permit, sequence 10

              Match clauses:

                ip address (access-lists): 1

            ON R3 I issued  redistribute eigrp 1 metric 200 metric-type 1 subnets route-map EIGRP>OSPF


            This again also seemed to be a viable solution. But would another way of been using tags? Tagging the routes I don't want to be redistributed back into the routing domain they came from? is this better?

            • 3. Re: Eigrp, OSPF summarization dilemma

              Hi Prash,


              In my blog i have done the CBT nugget labs and you will find tagging with route-maps on this page (between OSPF and EIGRP):


              • 4. Re: Eigrp, OSPF summarization dilemma
                C1SC0M - CCNP,CWNA,Net+


                Using Tags definitely is a more elegant solution:




                Use these route maps in your redistrubute statements.  With tagging you won't need to creat ACL in order to filter the prefixes.




                route-map EIGRP-into-OSPF permit 10

                set tag 20


                route-map EIGRP-into-OSPF deny 20

                match tag 40


                route-map OSPF-into-EIGRP permit 10

                set tag 40


                route-map OSPF-into-EIGRP deny 20

                match tag 20


                BTW the thread should said Redistribution Dilemma, your summarization is OK

                • 5. Re: Eigrp, OSPF summarization dilemma
                  jean-christophe manciot - CCDP

                  Your solution is elegant, indeed.

                  Just a slight typo: it would work better if you switched the statements in the route maps

                  • 6. Re: Eigrp, OSPF summarization dilemma

                    Erm do you mean deny first then permit?

                    • 7. Re: Eigrp, OSPF summarization dilemma
                      C1SC0M - CCNP,CWNA,Net+

                      HI guys,  just to clarify.  Yes, the DENY statements should be first.  I mis-typed that.  The other thing, for some reason I was thinking of double redistribution when I suggested this, and this would prevent loops.  But here that is not the case.


                      In these scenario even do you don't filter anything you won't have loops.  Now I'm looking into it.  Hope to come back soon with a correct explanation.