4 Replies Latest reply: Aug 15, 2011 12:15 AM by Martin RSS

    EIGRP auto summarization?

    Mohammed

      10.10.10.0/24------R1----------172.16.10.0/24--------------------R2---------------192.168.20.0/24---------------------R3

      if  the configuration on R1

      router eigrp 100

      net 10.0.0.0

      net  172.16.0.0

      no auto-summary

      and on all other routers  auto-summary is enabled

      which routes will be at R2

       

      -10.0.0.0/8

      10.10.10.0/24

      -172.16.0.0/16

      172.16.10.0/24

       

      i  mean r2 will receive 10.10.10.0/24 from R1 will it auto summerize it  before sending to R3 or will it send it as it is ?

        • 1. Re: EIGRP auto summarization?
          Scott Morris - CCDE/4xCCIE/2xJNCIE

          This is either a duplicate post or I'm going insane....

           

          It's all about the perspective of ownership....

           


          I  modified your diagram a little since my R2 was doing other things.  


          10.10.10.1    \
          10.10.12.1-----R1----172.16.10.0/24-----R4-----192.168.20.0/24------R3-----200.200.200.3
          1.1.1.1        /                   (45.45.45.4)
                                                (4.4.4.4)

           

          R1
          router eigrp 100
          network 10.0.0.0
          network 1.0.0.0
          network 172.16.0.0
          passive default
          no passive fa0/0
          no auto-summary

           

          R4
          router eigrp 100
          network 172.16.0.0
          network 192.168.20.0
          network 45.0.0.0
          network 4.0.0.0
          passive s0/1/0
          passive lo0

           

          R3
          router eigrp 100
          network 192.168.20.0
          network 200.200.200.0
          passive default
          no passive f0/0

           

           

           

          R1:
          Uber-Geek-R1(config-router)#do sh ip ro  ei
          D    200.200.200.0/24 [90/33280] via 172.16.10.4, 00:02:16,  FastEthernet0/0
          D    4.0.0.0/8 [90/156160] via 172.16.10.4, 00:01:41, FastEthernet0/0
          D    20.0.0.0/8 [90/20517120] via 172.16.10.4, 00:00:06, FastEthernet0/0
          D    192.168.20.0/24 [90/30720] via 172.16.10.4, 00:02:16,  FastEthernet0/0
          D    45.0.0.0/8 [90/2172416] via 172.16.10.4, 00:02:16, FastEthernet0/0
          Uber-Geek-R1(config-router)#

           

          So it sees summarized routes coming FROM R4 (R2 in your diagram)

           

          R4:

           

          Uber-Geek-R4(config-router)#do  sh ip ro ei
          D    200.200.200.0/24 [90/30720] via 192.168.20.3, 00:02:41,  FastEthernet0/1
                1.0.0.0/24 is subnetted, 1 subnets
          D       1.1.1.0 [90/156160] via 172.16.10.1, 00:02:32, FastEthernet0/0
                4.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
          D       4.0.0.0/8 is a summary, 00:01:58, Null0
          D    20.0.0.0/8 [90/20514560] via 192.168.20.3, 00:00:23,  FastEthernet0/1
                172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
          D       172.16.0.0/16 is a summary, 00:02:43, Null0
                10.0.0.0/24 is subnetted, 2 subnets
          D       10.10.10.0 [90/2172416] via 172.16.10.1, 00:02:32,  FastEthernet0/0
          D       10.10.12.0 [90/2172416] via 172.16.10.1, 00:02:32,  FastEthernet0/0
                45.0.0.0/8 is variably subnetted, 3 subnets, 3 masks
          D       45.0.0.0/8 is a summary, 00:02:43, Null0
          Uber-Geek-R4(config-router)#

           

          R4 sees pre-summarized routes coming FROM R3, but sees SPECIFIC  routes from R1.

           

          Uber-Geek-R3(config-router)#do  sh ip ro ei
                1.0.0.0/24 is subnetted, 1 subnets
          D       1.1.1.0 [90/158720] via 192.168.20.4, 00:03:14, FastEthernet0/0
          D    4.0.0.0/8 [90/156160] via 192.168.20.4, 00:02:39, FastEthernet0/0
                20.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
          D       20.0.0.0/8 is a summary, 00:01:04, Null0
          D    172.16.0.0/16 [90/30720] via 192.168.20.4, 00:03:22,  FastEthernet0/0
                10.0.0.0/24 is subnetted, 2 subnets
          D       10.10.10.0 [90/2174976] via 192.168.20.4, 00:03:14,  FastEthernet0/0
          D       10.10.12.0 [90/2174976] via 192.168.20.4, 00:03:14,  FastEthernet0/0
          D    45.0.0.0/8 [90/2172416] via 192.168.20.4, 00:03:22, FastEthernet0/0
          Uber-Geek-R3(config-router)#

           

          Interestingly enough, the specific 10.10.x.0/24 and 1.1.1.0/24  networks are NOT summarized by R4.  A learned EIGRP route is not  authoritative in summarizing.

          Since R1 did not auto-summarize, then it didn't happen.

           

          HTH,

           

          Scott

          • 2. Re: EIGRP auto summarization?
            hoangsonptit
            When a router has multiple working interfaces, and those interfaces use IP addresses in different classful networks, the router advertises a summary route for each classful network on interfaces attached to a different classful network.

            CCNP ROUTE 642-902 Official Certification Guide - Wendell Odom, Key Topic, Page 124

             

            When R1 advertise 10.10.10.0/24 network to R2, but R2 not directly connected to this one, so it send this network in classless form to R3. Otherwise, 172.16.10.0/24 network which connected to R2, it will be summarized before send to R3.

             

            I think EIGRP routers only summarize routes that correspond to network which their interfaces attached to.

             

            Regard,

            HS

            • 3. Re: EIGRP auto summarization?
              naresh

              no r2 cannot summarize because it is himself depend on r1 for this routes.so until r1 summaries it there is no router in eigrp which can summaries it because they dont know about those routes without r1.

              • 4. Re: EIGRP auto summarization?
                Martin

                and I am confused