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140 IP 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
5.1 27 August 2007
Copyright © 2005-2007, Nortel Networks
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