Concept Guide

network 10.0.13.0/24 area 0
network 10.0.23.0/24 area 0
!
interface Loopback 30
ip address 192.168.100.100/24
no shutdown
!
interface GigabitEthernet 3/1
ip address 10.1.13.3/24
no shutdown
!
interface GigabitEthernet 3/2
ip address 10.2.13.3/24
no shutdown
OSPF Area 0 — Te 2/1 and 2/2
router ospf 22222
network 192.168.100.0/24 area 0
network 10.2.21.0/24 area 0
network 10.2.22.0/24 area 0
!
interface Loopback 20
ip address 192.168.100.20/24
no shutdown
!
interface GigabitEthernet 2/1
ip address 10.2.21.2/24
no shutdown
!
interface GigabitEthernet 2/2
ip address 10.2.22.2/24
no shutdown
OSPFv3 NSSA
NSSA (Not-So-Stubby-Area) is a stub area that does not support Type-5 LSAs, but supports Type-7 LSAs to forward external
links. Initially ASBR (Autonomous System Border Router) forwards the external links through Type-7 LSAs to the Area Border
Router (ABR) of NSSA, which in turn converts them into Type-5 LSAs and forwards them to the rest of the OSPF domain.
NOTE: To support NSSA area, all the OSPF routers in that area should be configured with NSSA.
NSSA Options
NSSA can be configured with the following options:
1. Default-information-originate – To inject a default route using Type-7 LSAs — NSSA routers need to have access to the rest
of the OSPF routers in the autonomous system. To facilitate this, the default route is injected into the NSSA area through a
Type-7 LSA. This can be generated either by NSSA ASBR or NSSA ABR.
2. No-redistribute – To restrict Type-7 LSAs — When NSSA ASBR is also an ABR, redistributed external routes need not be
translated from Type-7 to Type-5 LSAs. ABR will directly inject external routes through Type-5 LSAs into the OSPF domain.
It does not send Type-7 LSAs into the NSSA area.
3. No-summary – To act as totally stubby area — NSSA area can be converted intoa totally stubby area to reduce the number
of Type-3 LSAs. Once it is configured, NSSA ABR will inject Type-3 LSAs into the NSSA area for default routes. The
remaining Type-3 LSAs are not allowed inside this area.
568
Open Shortest Path First (OSPFv2 and OSPFv3)