Brocade Multi-Service IronWare Routing Configuration Guide (Supporting R05.6.00) - Manual (Page 55)

Multi-Service IronWare Routing Configuration Guide 27
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Configuring confederations
To configure a confederation, configure groups of BGP4 devices into sub-ASs. A sub-AS is simply an
AS. The term “sub-AS” distinguishes ASs within a confederation from ASs that are not in a
confederation. For the viewpoint of remote ASs, the confederation ID is the AS ID. Remote ASs do
not know that the AS represents multiple sub-ASs with unique AS IDs.
NOTE
You can use any valid AS numbers for the sub-ASs. If your AS is connected to the Internet, it is
recommended that you use numbers from within the private AS range (64512 – 65535). These are
private ASs numbers and BGP4 devices do not propagate these AS numbers to the Internet.
Figure 6 shows an example of a BGP4 confederation.
FIGURE 6 Example BGP4 confederation
In this example, four devices are configured into two sub-ASs, each containing two of the devices.
The sub-ASs 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-ASs communicate with one another using EBGP. For
example, device A communicates with device C using EBGP. The devices in the confederation
communicate with other ASs using EBGP.
Devices in other ASs are unaware that devices A – D are configured in a confederation. In fact,
when devices in confederation 10 send traffic to devices in other ASs, the confederation ID is the
same as the AS number for the devices in the confederation. Thus, devices in other ASs see traffic
as coming from AS 10 and are unaware that the devices in AS 10 are subdivided into sub-ASs
within a confederation.
Configuring a BGP4 confederation
To configure a BGP4 configuration, perform these configuration tasks on each BGP4 device within
the confederation: