Border Router State

• Each border router maintains a list of all AS’s that it can reach

• This information is periodically transmitted to border routers at neighboring AS’s with BGP updates

• Since there are thousands of AS’s, these lists can grow very large

• • Thus, TCP is used for reliable delivery

• BGP-4 introduced route aggregation with CIDR

• • Networks with common prefixes can be aggregated “supernetted” into a single route entry
  • Route advertisement size is reduced