Brocade Communications Systems Layer 3 Routing Configuration ICX 6650 - Manual (Page 339)

Brocade ICX 6650 Layer 3 Routing Configuration Guide 321
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Optional BGP4 configuration tasks
Figure 27 shows an example of a BGP4 confederation.
FIGURE 27 Example of a BGP4 confederation
In this example, four switches are configured into two sub-autonomous systems, each containing
two of the switches. The sub-autonomous systems are members of confederation 10. Switches
within a sub-AS must be fully meshed and communicate using IBGP. In this example, Switches A
and B use IBGP to communicate. Switches C and D also use IBGP. However, the sub-autonomous
systems communicate with one another using EBGP. For example, Switch A communicates with
Switch C using EBGP. The switches in the confederation communicate with other autonomous
systems using EBGP.
Switches in other autonomous systems are unaware that Switches A through D are configured in a
confederation. In fact, when switches in confederation 10 send traffic to switches in other
autonomous systems, the confederation ID is the same as the AS number for the switches in the
confederation. Thus, switches in other autonomous systems see traffic from AS 10 and are
unaware that the switches in AS 10 are subdivided into sub-autonomous systems 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 switches with the same local AS number are members of the same sub-AS. BGP switches
use the local AS number when communicating with other BGP switches within the
confederation.
Switch A
Switch C Switch D
BGP4 Switch
Switch B
IBGP
IBGP
EBGP
Sub-AS 64513
Sub-AS 64512
EBGP
Confederation 10
AS 20
This BGP4 switch sees all
traffic from Confederation 10
as traffic from AS 10.
Switches outside the confederation
do not know or care that the switches
are subdivided into sub-ASs within a
confederation.