1022 PowerConnect B-Series FCX Configuration Guide53-1002266-01Optional configuration tasks30FIGURE 148 Example of a BGP4 confederationIn this example, four switches are configured into two sub-autonomous systems, each containingtwo of the switches. The sub-autonomous systems are members of confederation 10. Switcheswithin a sub-AS must be fully meshed and communicate using IBGP. In this example, Switches Aand B use IBGP to communicate. Switches C and D also use IBGP. However, the sub-autonomoussystems communicate with one another using EBGP. For example, Switch A communicates withSwitch C using EBGP. The switches in the confederation communicate with other autonomoussystems using EBGP.Switches in other autonomous systems are unaware that Switches A through D are configured in aconfederation. In fact, when switches in confederation 10 send traffic to switches in otherautonomous systems, the confederation ID is the same as the AS number for the switches in theconfederation. Thus, switches in other autonomous systems see traffic from AS 10 and areunaware that the switches in AS 10 are subdivided into sub-autonomous systems within aconfederation.Configuring a BGP confederationPerform the following configuration tasks on each BGP router within the confederation:• Configure the local AS number. The local AS number indicates membership in a sub-AS. AllBGP switches with the same local AS number are members of the same sub-AS. BGP switchesuse the local AS number when communicating with other BGP switches within theconfederation.Switch ASwitch C Switch DBGP4 SwitchSwitch BIBGPIBGPEBGPSub-AS 64513Sub-AS 64512EBGPConfederation 10 AS 20This BGP4 switch sees alltraffic from Confederation 10as traffic from AS 10.Switches outside the confederationdo not know or care that the switchesare subdivided into sub-ASs within aconfederation.
