BGP Confederation
The confederation is another method of dealing with increasing IBGP connections in an AS. It divides an AS into several sub-ASs. IBGP full meshes are established in each sub-AS, and EBGP full meshes are established between sub-ASs, as shown in Figure 1.
For BGP speakers outside the confederation (for example, the devices in AS100), the sub-ASs (AS65001, AS65002, and AS65003) in the same confederation are invisible. The external devices do not need to know the topology of each sub-AS. The confederation ID is the AS number that is used to identify the entire confederation. For example, AS 200 as shown in Figure 1 is the confederation ID.
As shown in Figure 1, there are multiple BGP devices in AS200. To reduce IBGP connections, AS200 is divided into three sub-ASs, namely, AS65001, AS65002, and AS65003. In AS65001, IBGP full meshes are established between the three devices.
Applications and Limitations
The confederation needs to be configured on each device, and the device that joins the confederation must support the confederation function.
The confederation has disadvantages. For example, if the devices originally are not in a confederation but later need to be configured as a confederation, the logical topology changes accordingly.
In large-scale BGP networks, RR and confederation can be used together.