OSPFv2 stub router advertisement

OSPFv2 stub router advertisement is an open standard based feature and it is specified in RFC 3137. This feature provides a user with the ability to gracefully introduce and remove an OSPFv2 device from the network, by controlling when the data traffic can start and stop flowing through the device in cases where there are other OSPFv2 devices present on the network providing alternative paths for the traffic. This feature does not work if there is no alternative for the traffic through other OSPFv2 routers. The device can control the data traffic flowing through it by changing the cost of the paths passing through the configured device. By setting the path cost high the traffic will be redirected to other OSPFv2 devices providing a lower cost path. This change in path cost is accomplished by setting the metric of the links advertised in the Router LSA to a maximum value. When the OSPFv2 device is ready to forward the traffic, the links are advertised with the real metric value instead of the maximum value.

OSPFv2 stub router advertisement is useful for avoiding a loss of traffic during short periods when adjacency failures are detected and traffic is rerouted. Using this feature, traffic can be rerouted before an adjacency failure occurs due to common services interruptions such as a router being shutdown for maintenance.

OSPFv2 stub router advertisement is also useful during startup because it gives the device enough time to build up its routing table before forwarding traffic. This can be useful where BGP is enabled on the device because it takes time for the BGP routing table to converge.

You can also configure and set a metric value for the following LSA types:

• Summary (type 3 and type 4)
• External (type 5 and type 7)
• Opaque (type 10, TE link)