OSPF Totally NSSA Area
This post will be about OSPF Totally Not-So-Stubby-Area’s. In the previous posts we talked about the OSPF nssa area type. For this post I will use the same topology as in the previous two posts, see below :
Let’s configure area 2 as a totally not-so-stubby-area. We need to configure the ABR with the area x nssa no-summary command and the rest of the routers in the area with the area x nssa command. See below :
R4 & R2 :
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R4(config)#router ospf 1
R4(config-router)#area 2 nssa no-summary
R2(config)#router ospf 1
R2(config-router)#area 2 nssa
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Now let’s look at the routing table of router R2 :
R2 :
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R2#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is 192.168.14.4 to network 0.0.0.0
2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
C 192.168.14.0/24 is directly connected, FastEthernet2/0
O*IA 0.0.0.0/0 [110/2] via 192.168.14.4, 00:09:05, FastEthernet2/0
R2#sh ip ospf dat
OSPF Router with ID (2.2.2.2) (Process ID 1)
Router Link States (Area 2)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.2 2.2.2.2 574 0x80000004 0x0027FD 1
4.4.4.4 4.4.4.4 573 0x80000004 0x00B35C 1
Net Link States (Area 2)
Link ID ADV Router Age Seq# Checksum
192.168.14.4 4.4.4.4 573 0x80000003 0x00414D
Summary Net Link States (Area 2)
Link ID ADV Router Age Seq# Checksum
0.0.0.0 4.4.4.4 578 0x80000001 0x00C065
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As you can see in an totally not-so-stubby-area LSA types 3,4,5 will be blocked. A default-route is generated by the ABR.