24.7.2 Summary route forwarding method

Summarized routes are configured as reject routes. Packets that lack a higher-priority route are discarded.

Summarized routes are configured in this way to prevent routing loops. When the Switch advertises a summarized route, packets destined for that route are relayed to the Switch. If the Switch then transfers a packet destined to a route that is not a summarization source route via the designated next-best route (such as the default route), a routing loop can occur between the Switch and the destination system of the default route. Summarized routes are designated as reject routes to prevent this scenario.

However, summarized routes configured with the noinstall parameter specified do not discard packets. If there is a default route or other next-best route, packets will be forwarded via that route. Use the noinstall parameter when you wish to advertise a summarized route but would rather it forward packets via the next-best route than discard them.