Internet Routing Architectures, Second Edition

Following Defaults Inside an AS

The following examples show how border routers can inject defaults inside your AS for your IGP to follow. Figure 12-10 illustrates the following scenario: AS3 is multihomed to two providers, AS1 and AS2. RTA is running EBGP with RTC, and RTF is running EBGP with RTD. Inside AS3, RTA and RTF are running IBGP. You will experiment with two situations: first, RTA and RTF having a direct physical connection, and second, RTA and RTF not having a direct physical connection. The latter scenario is used to demonstrate what could go wrong if your IGP traffic is following a default that conflicts with your BGP policies. Finally, RTG is an interior router that is running an IGP; RTG is following the default route 0/0 to ...