Configuring A Bgp Confederation - Dell PowerConnect B-RX Configuration Manual

Figure 114
FIGURE 114
In this example, four routers are configured into two sub-ASs, each containing two of the routers.
The sub-ASs are members of confederation 10. Routers within a sub-AS must be fully meshed and
communicate using IBGP. In this example, routers A and B use IBGP to communicate. Routers C
and D also use IBGP. However, the sub-ASs communicate with one another using EBGP. For
example, router A communicates with router C using EBGP. The routers in the confederation
communicate with other ASs using EBGP.
Routers in other ASs are unaware that routers A – D are configured in a confederation. In fact,
when routers in confederation 10 send traffic to routers in other ASs, the confederation ID is the
same as the AS number for the routers in the confederation. Thus, routers in other ASs see traffic
from AS 10 and are unaware that the routers in AS 10 are subdivided into sub-ASs within a
confederation.

Configuring a BGP confederation

Perform the following configuration tasks on each BGP router within the confederation:
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•
BigIron RX Series Configuration Guide
53-1001810-01
shows an example of a BGP4 confederation.
Example BGP4 confederation
Confederation 10
Sub-AS 64512
IBGP
Router B
Router A
EBGP
Sub-AS 64513
IBGP
Router C
Router D
Configure the local AS number. The local AS number indicates membership in a sub-AS. All
BGP routers with the same local AS number are members of the same sub-AS. BGP routers
use the local AS number when communicating with other BGP routers within the
confederation.
Configure the confederation ID. The confederation ID is the AS number by which BGP routers
outside the confederation know the confederation. Thus, a BGP router outside the
confederation is not aware and does not care that your BGP routers are in multiple sub-ASs.
BGP routers use the confederation ID when communicating with routers outside the
confederation. The confederation ID must be different from the sub-AS numbers.
Configuring confederations
EBGP
26
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.
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