Stub Area - Avaya 8800 Configuration Manual

OSPF and RIP fundamentals

Stub area

A stub area is configured at the edge of the OSPF routing domain and has only one ABR. A
stub area does not receive LSAs for routes outside its area, which reduces the size of its link-
state database. A packet destined outside the stub area is routed to the ABR, which examines
it before forwarding the packet to its destination. The network behind a passive interface is
treated as a stub area and does not form adjacencies. The network is advertised into the OSPF
area as an internal route.
Not so stubby area
A not so stubby area (NSSA) prevents the flooding of external LSAs into the area by replacing
them with a default route. An NSSA can import small stub (non-OSPF) routing domains into
OSPF. Like stub areas, NSSAs are at the edge of an OSPF routing domain. Non-OSPF routing
domains are attached to the NSSAs to form NSSA transit areas. Accessing the addressing
scheme of small stub domains permits the NSSA border router to also perform manual
aggregation.
In an OSPF NSSA, the NSSA N/P bit notifies the ABR which external routes can be advertised
to other areas. When the NSSA N/P bit is set (is a 1), the ABR exports the external route. This
is the default setting for the Ethernet Routing Switch 8800/8600. When the NSSA N/P bit is
not set (is a 0), the ABR drops the external route. You can create a route policy on the Ethernet
Routing Switch 8800/8600 to manipulate the N/P bit.
Example multiarea OSPF configuration
The multiarea configuration example described in this section (see the following figure) uses
five Ethernet Routing Switch 8800/8600 devices (R1 to R5) in a multi-area configuration.
38 Configuration — OSPF and RIP June 2011