Nortel Networks NN47200-503 manual Ospf stub area

140IP Routing Configuration and Management

Stub and Not So Stubby areas Stub areas do not receive advertisements for external routes (AS-external LSAs, type 5) from an ABR, which reduces the size of the link state database. Instead, routing to external destinations from within a stub area is based on the default route that is originated by the stub area ABR (Summary LSA, type 3).

Import summary can be disabled on a stub area ABR to further prevent redistribution of summary routes from other areas into the stub area. In this case, the stub area ABR advertises only default routes into the stub area.

Note: Disabling import summaries is only allowed in the stub area.

As shown in the following figure, a stub area has only one ABR. All packets that are destined to be forwarded outside the stub area are routed to the stub areas border exit point, where the ABR first examines the packets and then forwarded to a destination.

OSPF stub area

Note: Stub areas do not support ASBRs. In all routers attached to the stub area, the area must be configured as a stub area.

In the configuration example illustrated below, the Nortel Ethernet Routing Switch 5500 Series R1 is configured in Stub Area 2, and R2 is configured as a Stub ABR for Area 2.

Nortel Ethernet Routing Switch 5500 Series

Configuration-IP Routing Protocols

NN47200-503 03.01 Standard

5.127 August 2007

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