Dell PowerConnect B-RX - Configuring a Bgp Confederation

BigIron RX Series Configuration Guide 763
53-1002253-01
Configuring confederations
26
FIGURE 114 Example BGP4 confederation
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:
• 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.
• Configure the list of the sub-AS numbers that are members of the confederation. All the
routers within the same sub-AS use IBGP to exchange router information. Routers in different
sub-ASs within the confederation use EBGP to exchange router information.
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.