The following examples demonstrate different methods of aggregation that are seen on the Internet. The way aggregates are formed and advertised and whether they carry with them more-specific routes will influence traffic patterns and sizes of BGP routing tables. Remember that aggregation applies to routes that exist in the BGP routing table. An aggregate can be sent if at least one more-specific route of that aggregate exists in the BGP table.
Aggregate Only, Suppressing the More-Specific
This section shows how an aggregate can be generated without propagating any of the more-specific routes that fall under the aggregate. In the network illustrated in Figure 11-10, RTA is sending prefixes 172.16.220.0/24, 172.16.1.0/24, 172.16.10.0/24, ...