Configure and Verify OSPF Routing

Config on R1

!
router ospf 1
log-adjacency-changes
passive-interface FastEthernet0/0
network 10.1.1.1 0.0.0.0 area 0
network 172.16.1.16 0.0.0.15 area 0
network 192.168.10.0 0.0.0.3 area 0
network 192.168.10.4 0.0.0.3 area 0
!

Config on R2

!
router ospf 1
log-adjacency-changes
passive-interface FastEthernet0/0
network 10.2.2.2 0.0.0.0 area 0
network 10.10.10.0 0.0.0.255 area 0
network 192.168.10.0 0.0.0.3 area 0
network 192.168.10.8 0.0.0.3 area 0
!

Config on R3

!
router ospf 1
log-adjacency-changes
passive-interface FastEthernet0/0
network 10.3.3.3 0.0.0.0 area 0
network 172.16.1.32 0.0.0.7 area 0
network 192.168.10.4 0.0.0.3 area 0
network 192.168.10.8 0.0.0.3 area 0
!

Ping from PC1 to PC2

Ping from PC1 to PC3

Verify Configuration

Why can PC1 ping PC2?
-PC1 and PC2 are in different subnets, therefore a router is needed. PC2 is in network 10.10.10.0 /24 with the ip 10.10.10.254 /24 and his gateway is 10.10.10.1. PC1 is in network 172.16.1.16 /28 with ip 172.16.1.30 and gateway 172.16.1.17.

As we see above, R2 advertises network 10.10.10.0 /24 on the ospf process 1. Becouse of this advertisement (LSA) R1 learns about this network.
R1# show ip route

O 10.10.10.0/24 [110/65] via 192.168.10.2, 00:18:34, Serial0/0/0

!
Therefor when PC1 makes the echo request with ip 10.10.10.254 as destination ip, the packet reaches the router and forwards the packte out its Serial0/0/0.

Obviously in order for the packet to return the neighbor router needs to have a route back to network 172.16.1.16.

Verifying Configuration

1. Are ther any DR or BDR routers? If so, which ones?  There are no DR/BDR routers, becouse the links are all Point to Point.
2. Can you tell if the three have become neighbors and in which state are they?

If you issue the command show ip ospf neigbors I can see that all three routers have two neighbors

R1#sh ip ospf neighbor
Neighbor ID     Pri   State           Dead Time   Address         Interface
10.2.2.2          0   FULL/  -        00:00:30    192.168.10.2    Serial0/0/0
10.3.3.3          0   FULL/  -        00:00:32    192.168.10.6    Serial0/0/1
R2#sh ip ospf neighbor
Neighbor ID     Pri   State           Dead Time   Address         Interface
10.1.1.1          0   FULL/  -        00:00:36    192.168.10.1    Serial0/0/0
10.3.3.3          0   FULL/  -        00:00:34    192.168.10.10   Serial0/0/1

R3#sh ip ospf neighbor
Neighbor ID     Pri   State           Dead Time   Address         Interface
10.1.1.1          0   FULL/  -        00:00:37    192.168.10.5    Serial0/0/0
10.2.2.2          0   FULL/  -        00:00:38    192.168.10.9    Serial0/0/1
As we can see the state is FULL  with all neigbors , which means  each routers knows  the exact same LSDB (Link State data base) of his neighboring router. Which you can also check issuing the commando show ip ospf database.


 Learn about OSPF reading the following article. It is a resume from the Cisco Netacad Plattform.

https://docs.google.com/open?id=0B7Q9m3jppUCDNDljNzA3MzctMTZiNy00NGNhLTg1ZmItNGFmOGMxNjVlMDJm