Scaling Service Provider Networks Configuring and Monitoring Confederations

Outline Overview BGP Confederation Design Rules Planning BGP Confederations Configuring BGP Confederations Monitoring BGP Confederations Summary

BGP Confederation Design Rules IBGP full mesh within each member-AS is required. Route reflectors might be used within each AS to relax the IBGP full-mesh requirements. There is no topology limitation on EBGP sessions between autonomous systems within a confederation. The intra-confederation EBGP sessions will follow the physical topology of the network.

Planning BGP Confederations Divide the transit AS into smaller areas. Follow the physical topology of the network. Define the AS number for each area. Use AS numbers reserved for private use (64512 – 65535). Verify the Cisco IOS release level. All routers have to support BGP confederations. Convert each area into an AS. A total rewrite of the BGP configuration is required.

Configuring BGP Confederations Start the BGP process with the member-AS number. Specify an external AS number. Must be defined in all routers within confederation List all member-AS numbers in the confederation. Must be defined in all routers with an EBGP session

Configuring BGP Confederations (Cont.) router(config)# no router bgp as-number router bgp member-as-number Removes old BGP process and configures BGP process with member-AS number router(config-router)# bgp confederation identifier external-as-number Configures external confederation-wide AS number router(config-router)# bgp confederation peers list-of-intra-confederation-as Defines all the other autonomous systems in the confederation

Configuring BGP Confederations—Sample Configuration

Monitoring BGP Confederations router> show ip bgp neighbors Displays whether a neighbor is within the confederation router> show ip bgp prefix [mask] Displays internal and external segments of the AS-path attribute Displays whether the path is external, internal, or intra-confederation external

Monitoring Intra-Confederation EBGP Neighbors

Monitoring Confederation Routes

Summary BGP confederations do not modify IBGP behavior; thus, the classic IBGP split-horizon rules still apply, and a full mesh of IBGP sessions between all routers in the member AS is still required. A proper migration plan is important because the change to BGP confederation involves a major reconfiguration of BGP routing. BGP confederations are configured by specifying the confederation identifier and other member-AS peers. The show ip bgp neighbors command has been modified to display whether a BGP neighbor is part of a BGP confederation.