Lab 2. OSPF Virtual Link using GRE Tunnel

I have test virtual link using 'area xx virtual-link '. Actually there is another solution using GRE tunnel instead of virtual-link.

The topology and basic configuration of ip point to point and ospf is the same as virtual-link. Please have a look at http://pursuingmydestiny.blogspot.com/2011/12/lab-1-ospf-virtual-link.html for topology and ip p2p. If you already test virtual-link, just remove virtual-link command to continue this lab!

Using tunneling, need new IP P2P. Then the new IP tunneling advertise in OSPF area 0. Let's do tunneling to make it ospf adjacency in R2 and R3 and can ping each other.

R2#
R2(config)#interface tunnel 1
R2(config-if)#ip address 102.102.102.2 255.255.255.0
R2(config-if)#tunnel source 12.12.12.2
R2(config-if)#tunnel destination 12.12.12.1

R2(config-if)#router ospf 2
R2(config-router)#net 102.102.102.2 0.0.0.0 are 0

R1#
R1(config-router)#inter tunn1
R1(config-if)#tunnel source 12.12.12.1
R1(config-if)#tunne destination 12.12.12.2
R1(config-if)#ip add 102.102.102.1 255.255.255.0

R1(config-if)#router ospf 1
R1(config-router)#net 102.102.102.1 0.0.0.0 are 0

Now, area 2 already connect to area backbone. Please check the routing table

R2(config-router)#do sh ip rout
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 not set

      102.0.0.0/24 is subnetted, 1 subnets
C 102.102.102.0 is directly connected, Tunnel1
      1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/11112] via 102.102.102.1, 00:03:22, Tunnel1
      2.0.0.0/32 is subnetted, 1 subnets
C 2.2.2.2 is directly connected, Loopback0
      23.0.0.0/24 is subnetted, 1 subnets
C 23.23.23.0 is directly connected, FastEthernet0/0
      12.0.0.0/24 is subnetted, 1 subnets
C 12.12.12.0 is directly connected, Serial0/0

Now let's make another tunneling for R3.

R2#
R2(config-router)#int tun 23
R2(config-if)#ip add 203.203.203.2 255.255.255.0
R2(config-if)#tunn sour 23.23.23.2
R2(config-if)#tunn dest 23.23.23.3

R2(config-if)#router ospf 2
R2(config-router)#net 203.203.203.2 0.0.0.0 are 0

R3#
R3(config-router)#int tun 23
R3(config-if)#ip add 203.203.203.3 255.255.255.0
R3(config-if)#tunn sou 23.23.23.3
R3(config-if)#tunn dest 23.23.23.2

R3(config-if)#router ospf 3
R3(config-router)#net 203.203.203.3 0.0.0.0 are 0

Then check routing table in R3. All IP advertise in R1 & R2 should be there

R3(config-router)#do sh ip rout
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 not set

       102.0.0.0/24 is subnetted, 1 subnets
O      102.102.102.0 [110/22222] via 203.203.203.2, 00:02:12, Tunnel23
C      203.203.203.0/24 is directly connected, Tunnel23
       1.0.0.0/32 is subnetted, 1 subnets
O      1.1.1.1 [110/22223] via 203.203.203.2, 00:02:12, Tunnel23
      2.0.0.0/32 is subnetted, 1 subnets
O IA 2.2.2.2 [110/11112] via 203.203.203.2, 00:02:12, Tunnel23
      3.0.0.0/32 is subnetted, 1 subnets
C      3.3.3.3 is directly connected, Loopback0
      23.0.0.0/24 is subnetted, 1 subnets
C      23.23.23.0 is directly connected, FastEthernet0/0
      12.0.0.0/24 is subnetted, 1 subnets
O IA 12.12.12.0 [110/11175] via 203.203.203.2, 00:02:14, Tunnel23

Then check the ping. R3 should be able to ping R1 & R2!

R3(config-router)#do ping 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 60/68/80 ms

R3(config-router)#do ping 1.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 48/69/108 ms