Brocade BigIron RX Series Configuration Guide - Manual (Page 916)

838 BigIron RX Series Configuration Guide
53-1002484-04
Configuring confederations
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The Brocade implementation of this feature is based on RFC 3065.
Normally, all BGP routers within an AS must be fully meshed, so that each BGP router has BGP
sessions to all the other BGP routers within the AS. This is feasible in smaller ASs but becomes
unmanageable in ASs containing many BGP routers.
When you configure BGP routers into a confederation, all the routers within a sub-AS (a subdivision
of the AS) use IBGP and must be fully meshed. However, routers use EBGP to communicate
between different sub-ASs.
NOTE
Another method for reducing 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, configure a confederation.
You can run a separate IGP within each sub-AS.
To configure a confederation, configure groups of BGP routers 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, Brocade
recommends that you use numbers from within the private AS range (64512 – 65535). These are
private ASs numbers and BGP4 routers do not propagate these AS numbers to the Internet.
Figure 124 shows an example of a BGP4 confederation.
FIGURE 124 Example BGP4 confederation
Router A Router B
Router C Router D
IBGP
IBGP
EBGP
Sub-AS 64513
Sub-AS 64512
EBGP
Confederation 10
AS 20
This BGP4 router sees all
traffic from Confederation 10
as traffic from AS 10.
Routers outside the confederation
do not know or care that the routers
are subdivided into sub-ASs within a
confederation.