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

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BGP Auto-Summary

Jan 13, 2012 1:05 AM

Keith 166 posts since
Jan 5, 2011

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

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  • Fedor 21 posts since
    Feb 14, 2011
    Currently Being Moderated
    1. Jan 13, 2012 1:28 AM (in response to Keith)
    Re: BGP Auto-Summary

    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"

  • Fedor 21 posts since
    Feb 14, 2011
    Currently Being Moderated
    3. Jan 13, 2012 1:46 AM (in response to Keith)
    Re: BGP Auto-Summary

    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

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