Brocade Communications Systems FastIron SX 800 Configuration Manual page 392

Optional BGP4 configuration tasks
NOTE
Another way to reduce the complexity of an IBGP mesh is to use route reflection. However, if you want to run different Interior
Gateway Protocols (IGPs) within an AS, you must configure a confederation. You can run a separate IGP within each sub-AS.
To configure a confederation, configure groups of BGP4 devices into sub-autonomous systems. A sub-AS is simply an AS. The term
"sub-AS" distinguishes autonomous systems within a confederation from autonomous systems that are not in a confederation. For the
viewpoint of remote autonomous systems, the confederation ID is the AS ID. Remote autonomous systems do not know that the AS
represents multiple sub-autonomous systems with unique AS IDs.
NOTE
You can use any valid AS numbers for the sub-autonomous systems. If your AS is connected to the Internet, Brocade
recommends that you use numbers from within the private AS range (64512 through 65535). These are private autonomous
system numbers and BGP4 devices do not propagate these AS numbers to the Internet.
FIGURE 32 Example BGP4 confederation
In this example, four devices are configured into two sub-autonomous systems, each containing two of the devices. The sub-
autonomous systems are members of confederation 10. Devices within a sub-AS must be fully meshed and communicate using IBGP.
In this example, devices A and B use IBGP to communicate. devices C and D also use IBGP. However, the sub-autonomous systems
communicate with one another using EBGP. For example, device A communicates with device C using EBGP. The devices in the
confederation communicate with other autonomous systems using EBGP.
Devices in other autonomous systems are unaware that devices A through D are configured in a confederation. In fact, when devices in
confederation 10 send traffic to devices in other autonomous systems, the confederation ID is the same as the AS number for the
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FastIron Ethernet Switch Layer 3 Routing
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