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Advantages of Using External BGP Peer Groups

BGP is the only routing protocol in use today that is suited to carry all of the routes in the Internet. This is largely because BGP runs on top of TCP and can make use of TCP flow control. In contrast, the internal gateway protocols (IGPs) do not have flow control. When IGPs have too much route information, they begin to churn. When BGP has a neighboring speaker that is sending information too quickly, BGP can throttle down the neighbor by delaying TCP acknowledgements.

Another benefit of BGP is that (like IS-IS) it uses type, length, value (TLV) tuples and network layer reachability information (NLRI) that provide seemingly endless extensibility without the need for the underlying protocol to be altered.

In the Junos® operating system (Junos OS), BGP is completely policy driven. The operator must explicity configure neighbors to peer with and explicity accept routes into BGP. Further, routing policy is used to filter and modify routing information. Thus, routing policies provide complete administrative control over the routing tables.

The preferred way to configure a large number of BGP peer neighbors is to configure peer groups consisting of multiple neighbors per group.

As the number of external BGP (EBGP) groups increases, the ability to support a large number of BGP sessions might become a CPU and memory resource scaling issue. Supporting fewer EBGP groups generally scales better than supporting a large number of EBGP groups. This becomes more evident in the case of hundreds of EBGP groups when compared with a few EBGP groups with multiple peers in each group. The reason for this scaling behavior is that Junos OS has data structures that occur on a per route-per group basis. When you add a group, you multiply those numbers and decrease the amount of memory available.

BGP peering creates mutually beneficial traffic exchange relationships between two independent autonomous systems (ASs). It is especially useful at service provider exchange points. This relationship has the primary benefit of reducing transit costs and equipment resources for both networks. Other potential benefits of creating BGP peer groups include reducing the complexity of the BGP configuration and increasing route redundancy by reducing the dependence on transit providers.

BGP peering can be used to create point-to-point traffic exchanges between two remote networks, such as a remote office and the company headquarters. It can also be used to quickly connect two disparate networks, such as between two merged offices.

Published: 2013-02-08