4 Replies Latest reply: Jan 13, 2012 2:05 AM by Keith RSS

    BGP Auto-Summary

    Keith

      Hi,

       

      I am trying to get my head around BGP and the affects of the auto-summary command in AS1,  When I advertise the 3 networks the only way I get the routes to be advertise is by adding the static route to the classful networki'm assuming the network command advertises the 3 networks 10.1.32.0/24 to 34, BGP then requires the classful network in the ip routing table as the BGP routes will be summariazed  to 10.0.0.0 ?

       

      router bgp 1

      no synchronization

      bgp log-neighbor-changes

      network 10.1.32.0

      network 10.1.33.0

      network 10.1.34.0

      neighbor 192.168.1.2 remote-as 2

      auto-summary

       

      ip route 10.0.0.0 255.0.0.0 Null0

       

      Also if I use the network command with the mask, auto-summary does not have any effect i.e.

       

      network 10.1.32.0 mask 255.255.255.0

      network 10.1.33.0 mask 255.255.255.0

      network 10.1.34.0 mask 255.255.255.0

        • 1. Re: BGP Auto-Summary
          Fedor

          I just labbed this up myself. With auto-summary configured, it appears BGP will only advertise the route if you specify the classful network in the network statement. ie remove the discard route, and simply configure: network 10.0.0.0

           

          On R2 in AS2, i received:

           

          R2#sh ip route bgp

          B    10.0.0.0/8 [20/0] via 192.168.1.1, 00:08:12

           

          Keith wrote:


          Also if I use the network command with the mask, auto-summary does not have any effect i.e.


          The ROUTE book states "the change in logic occurs only when the network command omits its mask parameter"

          • 2. Re: BGP Auto-Summary
            Keith

            When I omit the discard route, I do not receive any routes by simply configuring the network 10.0.0.0

             

            router bgp 1

            no synchronization

            bgp log-neighbor-changes

            network 10.0.0.0

            neighbor 192.168.1.2 remote-as 2

            auto-summary

            R1#

             

            R1#sh ip route

            10.0.0.0/24 is subnetted, 3 subnets

            C       10.1.34.0 is directly connected, Loopback3

            C       10.1.33.0 is directly connected, Loopback2

            C       10.1.32.0 is directly connected, Loopback1

                 192.168.1.0/30 is subnetted, 1 subnets

            C       192.168.1.0 is directly connected, FastEthernet0/0Hi,

            • 3. Re: BGP Auto-Summary
              Fedor

              You are looking at the routing table on R1 which will list the directly connected loopbacks (AD 0).

               

              Check out the BGP table on R1, or R2's routing table:


              R1#sh ip bgp

              BGP table version is 2, local router ID is 10.1.34.1

              Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

                            r RIB-failure, S Stale

              Origin codes: i - IGP, e - EGP, ? - incomplete

               

                 Network          Next Hop            Metric LocPrf Weight Path

              *> 10.0.0.0         0.0.0.0                  0         32768 i

              • 4. Re: BGP Auto-Summary
                Keith

                OK It took a while for the BGP routes to appear,  So if you use the classful network statement it will advertise any network that starts with the Classful network, in this scenario anything with the 10.x.x.x nets.

                 

                 

                R1#sh ip bgp

                BGP table version is 4, local router ID is 10.1.34.1

                Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

                              r RIB-failure, S Stale

                Origin codes: i - IGP, e - EGP, ? - incomplete

                 

                   Network          Next Hop            Metric LocPrf Weight Path

                *> 10.0.0.0         0.0.0.0                  0         32768 i