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How to configure the BGP conditional advertisement feature


Core Issue

The Border Gateway Protocol (BGP) conditional advertisement feature provides greater control over route advertisements by permitting certain routes to be advertised based on the existence of other routes in the BGP  table. This is a useful feature for multi-homed networks when it is desirable to advertise certain networks to one of the Internet Service Providers (ISPs), but only if the connectivity to another ISP fails.


To configure the BGP conditional advertisement feature, perform these steps:

  1. Create a route map that permits a prefix the BGP speaker can track. Conditional advertisement  takes place if the route being tracked does not exist in the BGP table. Create another route map that  permits the prefix to be advertised. The routes that are conditionally advertised should also  exist as valid routes in the BGP table. To create a route map, issue the route-map command in global configuration mode. Issue the match and set commands in route-map configuration mode.
  2. Configure a conditional advertisement by binding the configured route maps to a BGP neighbor. This is done by issuing the neighbor advertise-map non-exist-map command in router configuration mode. The route map which specifies the tracked prefix is associated with the non-exist-map keyword. The route map which specifies the advertised prefix  conditionally is associated with the advertise-map keyword.

To configure BGP for multi-homing and for controlling the routing information, refer to Configuring and Verifying the BGP Conditional Advertisement Feature.


How can i track multiple Routes ( if all of them Exist) Then advertise? having hard time acheiving this :)