OSPF Design Limitation

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OSPF does not have any limitation of routers like EIGRP and RIP has, it has a process to follow to have all area communicated.

        * If more than one area is configured, one area has to be Area 0.
        * All areas have to be connected to Area 0.
        * Area 0 must be contiguous.

Enabling OSPF

We can enable OSPF in two ways

Interface based	Process Based
int f0/0	router ospf 1
ip ospf 1 area 0	network 0.0.0.0 0.0.0.0 area 0

Lets run OSPF process between 2 routers using Area-0, on R1 we will use interface based OSPF and on R2 we will run Process based

Router 1	Router 2
R1(config)#interface fastEthernet 0/0 R1(config-if)#ip address 12.0.0.01 255.0.0.0 R1(config-if)#no shutdown R1(config-if)#exit R1(config)#interface loopback 0 R1(config-if)#ip address 1.1.1.1 255.255.255.255 R1(config-if)#exit R1(config)#interface range fastEthernet 0/0, loopback 0 R1(config-if-range)#ip ospf 1 area 0 R1(config-if-range)#exit	R2(config)#interface fastEthernet 0/0 R2(config-if)#ip address 12.0.0.2 255.0.0.0 R2(config-if)#no shutdown R2(config-if)#exit R2(config)#interface loopback 0 R2(config-if)#ip address 2.2.2.2 255.255.255.255 R2(config-if)#exit R2(config)#router ospf 1 R2(config-router)#network 12.0.0.0 0.255.255.255 area 0 R2(config-router)#network 2.2.2.2 0.0.0.0 area 0 R2(config-router)#exit

Once the Parameters are checked, both routers will form the neighborship and we can see neighborship logs on CLI

Router 1	%OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on FastEthernet0/0 from LOADING to FULL, Loading Done
Router 2	%OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on FastEthernet0/0 from LOADING to FULL, Loading Done

Compare OSPFv2 and OSPFv3
        * Traditional OSPFv2 for IPv4
                router ospf process-id
                Transported over IPv4
        * Traditional OSPFv3 for IPv6 only
                ipv6 router ospf process-id
                Transported over IPv6
                Peering over IPv6 link-local addresses
        * New style OSPFv3 for IPv4 and IPv6 address families
                router ospfv3 process-id
                Transported over IPv6 (link-local addresses)
                No peering with traditional OSPFv2 routers

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