In the first lesson, I introduced the OSPF stub areas. I also covered the stub area and totally stub area. Now we get to see the OSPF NSSA (Not So Stubby) area. Here’s the topology we will use:
And here’s the configuration. We will turn OSPF Area 1 into a stub area:
R1(config)#router ospf 1 R1(config-router)#network 192.168.12.0 0.0.0.255 area 0 R1(config-router)#redistribute connected subnets
R2(config)#router ospf 1 R2(config-router)#area 1 stub R2(config-router)#network 192.168.12.0 0.0.0.255 area 0 R2(config-router)#network 192.168.23.0 0.0.0.255 area 1
R3(config)#router ospf 1 R3(config-router)#area 1 stub R3(config-router)#network 192.168.23.0 0.0.0.255 area 1
The loopback 0 interface of R1 is redistributed into OSPF. I did this to test the stub area since it blocks LSA type 5. This is what the routing table of R3 looks like now:
R3#show ip route ospf O IA 192.168.12.0/24 [110/2] via 192.168.23.2, 00:00:42, FastEthernet0/0 O*IA 0.0.0.0/0 [110/2] via 192.168.23.2, 00:00:42, FastEthernet0/0
When we look at R3, you’ll see network 192.168.12.0 /24 and a default route as inter-area (LSA Type 3). Now to demonstrate the NSSA, I will create a new loopback interface on R3:
When we look at router Susan you’ll see network 192.168.12.0 /24 as inter-area (LSA Type 3) and 188.8.131.52 /24 as external type 2 (LSA Type 5).:???
That’s how it is supposed to be right? Network 192.168.12.0 /24 is inter-area for router Susan (LSA Type 3) and 184.108.40.206 /24 is an external prefix (LSA Type 5).
If Susan in configured as area 1 stub, don’t you think LSA 4&5 will get blocked. Output of Susan shows correctly that it will allow LSA Type 3 for Inter area routes and a default route by the ABR Donna. Kindly check and confirm.
Thanks Hemant, the text didn’t match with the output…just fixed it.
*Mar 1 00:20:02.495: %OSPF-4-BADLSATYPE: Invalid lsa: Bad LSA chksum Type 7, LS
ID 220.127.116.11 from 18.104.22.168, 192.168.23.3, FastEthernet0/1 – receiving error on Donna router