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    Disablement of Automatic Route-Target Filtering

    When BGP receives a VPN-IPv4 or VPN-IPv6 route from another PE router, BGP stores that route in its local routing table only if at least one VRF imports a route target of that route. If no VRF imports any of the route targets of the route, BGP discards the route; this feature is called automatic route-target filtering. The intention is that BGP keeps track of routes only for directly connected VPNs, and discards all other VPN-IPv4 or VPN-IPv6 routes to conserve memory.

    If a new VPN is connected to the router (that is, if the import route-target list of a VRF changes), BGP automatically sends a route-refresh message to obtain the routes that it previously discarded.

    You can use the no bgp default route-target filter command to disable automatic route-target filtering globally for all VRFs. However, automatic route-target filtering is always disabled on route reflectors that have at least one route-reflector client. You cannot enable automatic route-target filtering for such route reflectors.

    If route-target filtering is turned off, BGP automatically sends out a route-refresh message over every VPNv4 or VPNv6 unicast session (for which the route-refresh capability was negotiated) to get previously filtered routes. If the route-refresh capability was not negotiated over the session, BGP bounces the session.

    Published: 2014-08-18