Switch User Manual

IP routing conﬁguration examples 143

Not So Stubby Areas (NSSA) Similar to stub areas, the not so stubby

area (NSSA) can also prevent the ﬂooding of AS-External Link State

advertisements into the NSSA by replacing them with a default route.

However, NSSA can also import small stub (non-OSPF) routing domains

into OSPF. This allows the NSSA to import external routes, such as RIP

routes, and then advertise these routes throughout the network.

External routing information is imported into NSSA by using type 7 LSAs.

These LSAs are translated at the NSSA boundary into LSA type 5. The N/P

bit in the type 7 LSA Options ﬁeld indicates whether the type 7 LSA must be

translated. Only those LSAs with the N/P-bit set are translated.

The NSSA conﬁguration example illustrated below demonstrates a Nortel

Ethernet Routing Switch 5500 Series conﬁgured as a NSSA ASBR router.

NSSA conﬁguration example

To conﬁgure the example illustrated above, follow this procedure:

Step Action

Conﬁgure router R1.

a. Conﬁgure the RIP interface on R1.

Conﬁgure port 1/20 as a brouter port in VLAN 100 and enable

RIP on this interface.

5530-24TFD(config)# interface fast 1/20

5530-24TFD(config-if)# brouter port 1/20 vlan 100

subnet 20.1.1.2/30

5530-24TFD(config)# router rip

5530-24TFD(config-router)# network 20.1.1.2

b. Enable RIP globally and conﬁgure the RIP version 2 interface.

5530-24TFD(config)# router rip enable

Nortel Ethernet Routing Switch 5500 Series

Conﬁguration-IP Routing Protocols

NN47200-503 03.01 Standard

5.1 27 August 2007