Brocade BigIron RX Series Configuration Guide - Manual (Page 917)

BigIron RX Series Configuration Guide 839
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Configuring confederations
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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.
The procedures show how to implement the example confederation shown in Figure 26.3.
To configure four devices to be a member of confederation 10, consisting of two sub-ASs (64512
and 64513), enter commands such as the following.
Commands for Router A
BigIron RXA(config)# router bgp
BigIron RXA(config-bgp)# local-as 64512
BigIron RXA(config-bgp)# confederation identifier 10
BigIron RXA(config-bgp)# confederation peers 64512 64513
BigIron RXA(config-bgp)# write memory
Syntax: local-as <num>
The <num> parameter with the local-as command indicates the AS number for the BGP routers
within the sub-AS. You can specify a number from 1 – 65535. Brocade recommends that you use a
number within the range of well-known private ASs, 64512 – 65535.
Syntax: confederation identifier <num>
The <num> parameter with the confederation identifier command indicates the confederation
number. 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. You can specify a number from 1 – 65535.