13.1.4 BGP4 Features in VRF

(1) Overview

BGP4 operates independently within networks logically divided by the VRF functionality. Note that a peer connection between different VRFs is not possible.

(2) Notes on Using BGP4 with VRF

On the Switch, a route imported from a different VRF or the global network inherits the PATH attribute from the source route. Therefore, if a target route is advertised from the Switch, a route loop might be detected on neighboring devices.

1. Note on when different VRFs or global networks use the same AS number

   Be careful when you import a route between VRFs or global networks that use the same AS number.If the target route is advertised to the import-source VRF or global network, the route is not treated as a valid route because an AS loop is detected on neighboring devices. The Switch provides the neighbor as-override configuration command that overwrites the first AS number set for the AS_PATH attribute of the VRF or the global network with the AS number of the Switch. If you use BGP4 for a connection between VRFs or global networks that have the same AS number, be sure to use this command.

   Note that the neighbor as-override configuration command cannot resolve AS loops in neighboring devices when the VRFs or global networks are not directly connected to the Switch and using the same AS number. If the Switch is used as a neighboring device, you can use the neighbor permit-asloop configuration command, which treats an AS loop route as a valid route. Use this command when using the same AS number in VRFs or global networks. Note that this command must be used in carefully designed networks because its use can increase the risk of a route loop.

2. Note on when different VRFs or global networks use the same router ID or cluster ID (route reflection)

   When different VRFs or global networks use the same router ID (originator ID) or when the route reflectors in different VRFs or global networks use the same cluster ID, the routes are not treated as valid routes because the route reflectors detect a loop. Note this when designing networks.