Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide - Manual (Page 427)

FIGURE 33 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 devices in the confederation. Thus,
devices in other autonomous systems see traffic as coming from AS 10 and are unaware that the
devices in AS 10 are subdivided into sub-autonomous systems within a confederation.
Configuring a BGP4 confederation
To configure a BGP4 configuration, perform these configuration tasks on each BGP4 device within the
confederation:
• Configure the local AS number. The local AS number indicates membership in a sub-AS. All BGP4
devices with the same local AS number are members of the same sub-AS. BGP4 devices use the
local AS number when communicating with other BGP4 devices in the confederation.
• Configure the confederation ID. The confederation ID is the AS number by which BGP4 devices
outside the confederation recognize the confederation. A BGP4 device outside the confederation is
not aware of, and does not care that BGP4 devices are in multiple sub-autonomous systems. A
BGP4 device uses the confederation ID to communicate with devices outside the confederation. The
confederation ID must differ from the sub-AS numbers.
• Configure the list of the sub-AS numbers that are members of the confederation. All devices within
the same sub-AS use IBGP to exchange device information. Devices in different sub-autonomous
systems within the confederation use EBGP to exchange device information.
To configure four devices to be members of confederation 10 (consisting of sub-autonomous systems
64512 and 64513), enter commands such as the following.
Configuring a BGP4 confederation
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