In BGP, prefix aggregates are commonly used to reduce the size of the routing table and minimize the amount of updates exchanged between routers. BGP manages prefix aggregates by summarizing multiple IP prefixes into a single, larger prefix, and advertising it to other routers in the network.
When a router receives a prefix aggregate from another router, it must be able to determine which specific subnets or IP addresses are included within that aggregate. This process is known as de-aggregation or dis-aggregation. To do this, the receiving router looks at its own routing table and compares the prefix aggregate with the IP addresses or subnets it has already learned through BGP advertisements.
If the aggregate includes IP addresses that are not in the routing table, the receiving router will request more specific information from the advertising router. The advertising router responds with more specific subnets, which the receiving router can add to its routing table.
Prefix aggregation can help reduce the size of BGP routing tables and minimize the amount of updates exchanged between routers. However, it can also result in inefficient routing if the aggregate includes prefixes that are not actually reachable through the same path. Therefore, the router administrators must be careful when using prefix aggregates to ensure that they accurately reflect the network topology and ensure efficient routing.
