13.4.7 BGP4 advertised route generation

From the routing information stored in the local switch, you can generate a route to a given destination and advertise it via BGP4. By using the actual BGP4 route for packet forwarding, and the generated route for advertising the same routing information to other devices, you can ensure reliable forwarding to a BGP4 route destination as well as stable route advertising. The figure below shows an example of using this functionality.

Normally, set the BGP4 route received from router A as the forwarding table, and then advertise an advertised route generated from the route to router B.

Figure 13-20: Generation and advertisement of advertised routes (in normal cases)

If the BGP4 route learned from router A was deleted, a static route is activated and an advertised route generated from this static route is advertised to router B.

Figure 13-21: Generation and advertisement of advertised routes (when BGP4 routes are deleted)

By setting up the system in this way, the BGP4 route will be used for usual packet forwarding. If the BGP4 route received from Router A flaps, the BGP4 advertised route to Router B will not be affected.

Use the network configuration command to generate advertised routes.

Advertised routes are advertised to all peers unless route filtering is explicitly set. If an advertised route with the same destination that was generated from the BGP4 route was advertised to the learning source of the BGP4 route (router A in this example), a route loop may occur. In that case, use route filtering to suppress advertisement.