Network summary route in different routing protocols

network summary route in different routing protocol


  • auto summary: summary subnets into classful net route
  • ip summary-address: Automatic summary addressing always summarizes to the classful address boundary, while the ip summary-address router configuration command summarizes addresses on a specified interface.
    interface Ethernet1
    ip address
    ip summary-address rip
    no ip split-horizon
  • Automatic summary will override the configured summary address feature on a given interface except when both of the following conditions are true:
    •The configured interface summary address and the IP address of the configured interface share the same major network (the classful, nonsubnetted portion of the IP address).
    •Split horizon is not enabled on the interface.

OSPF is link state routing protocol that works on the concept of areas. All areas must have same LSDB (link state database); hence OSPF summarization can only done on the border routers i.e. on ABR (Area border router) and ASBR (Autonomous system boundary router).

  • Inter Area route summarization:
    To summarize routes towards another area, in ABR we can use the following command:
    area [area-id] range [ ip-address ] [mask ] [advertise | not-advertise |cost {cost}]
    It will remove subnets routes from advertising to other area but a summarized route.
  • External route summarization.
    Use the following command to help reduce the size of the routing table and allow an OSPF Autonomous System Boundary Router (ASBR) to advertise one external route as an aggregate for all redistributed routes that are covered by the address.
    summary-address network netmask

network summary of BGP can be found here