24.7.4 Suppressing advertisement of summarization source routes

After you summarize a route, it is possible to advertise the summarized route but exclude its source routes from being advertised. For example, you can advertise the RIPng routes that are not the source nodes of a summarized route, and suppress advertisement of the RIPng routes that are the source nodes of a summarized route.

You can suppress the advertisement of source routes on an individual basis or for all summarized routes. To suppress advertisement for an individual summarized route, specify the summary-only parameter when you execute the ipv6 summary-address configuration command.

The following figure shows an example in which advertisement is suppressed for a summarized route.

Figure 24-6: Example of suppressing advertisement of summarization source routes

Switch A receives addresses in the range from 3ffe:501:811:ff01::/64 to 3ffe:501:811:ff0f::/64 from Router 1 and 3ffe:501:811:fe01::/64 from Router 2, and learns routes in the range from 3ffe:501:811:ff11::/64 to 3ffe:501:811:ff1f::/64 from Router 3. Switch A then configures the advertised route filter to advertise the summarized route 3ffe:501:811:ff00::/56 and learned route 3ffe:501:811:fe01::/64 to Router 4. At this point, if you specified the summary-only parameter when you configured the switch to generate the summarized route 3ffe:501:811:ff00::/56 from learned routes, you do not need to configure the advertised route filter to prevent the switch from advertising the summary source routes. The following figure shows an example configuration for route summarization, and the entries in the routing table before and after summarization.

Figure 24-7: Example configuration of route summarization and routes before and after route summarization