OSPF Virtual-link Concept

I just simulated simple OSPF virtual-link concept.

Objective :  Creating Virtual link taking "Area 2" as transit. So Area 1 Networks are reachable from Backbone and RTR-B LSDB contains non backbone area information which is passible by using Virtual-links configuration.

Configuration :

RTR-A

RTRA#sh run | s r o
router ospf 1
 router-id 1.1.1.1
 log-adjacency-changes
 area 2 virtual-link 2.2.2.2
 network 11.11.11.1 0.0.0.0 area 1
 network 12.12.12.1 0.0.0.0 area 2

RTRA#sh ip int brie | e un
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            12.12.12.1      YES manual up                    up
FastEthernet0/1            unassigned      YES unset  administratively down down
Loopback0                  11.11.11.1      YES manual up                    up

RTR-B :

RTRB#sh run | s r o
router ospf 1
 router-id 2.2.2.2
 log-adjacency-changes
 area 2 virtual-link 1.1.1.1
 network 12.12.12.2 0.0.0.0 area 2
 network 22.22.22.22 0.0.0.0 area 0


RTRB#sh ip int brie | e un
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            12.12.12.2      YES manual up                    up
Loopback0                  22.22.22.22     YES manual up                    up

Testing :

RTR-A


RTRA#sh ip ospf virtual-links
Virtual Link OSPF_VL1 to router 2.2.2.2 is up
  Run as demand circuit
  DoNotAge LSA allowed.
  Transit area 2, via interface FastEthernet0/0, Cost of using 10
  Transmit Delay is 1 sec, State POINT_TO_POINT,
  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
    Hello due in 00:00:05
    Adjacency State FULL (Hello suppressed)
    Index 1/2, retransmission queue length 0, number of retransmission 0
    First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)
    Last retransmission scan length is 0, maximum is 0
    Last retransmission scan time is 0 msec, maximum is 0 msec

RTRA#ping 22.22.22.22
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 22.22.22.22, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 32/48/88 ms

RTR-B:

RTRB#ping 11.11.11.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 11.11.11.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 20/45/84 ms


RTRB#sh ip route ospf
     11.0.0.0/32 is subnetted, 1 subnets
O IA    11.11.11.1 [110/11] via 12.12.12.1, 00:08:56, FastEthernet0/0
OSPF LSDB & Neighbor details :

RTRA#sh ip ospf neig
Neighbor ID     Pri   State           Dead Time   Address         Interface
2.2.2.2           0   FULL/  -           -        12.12.12.2      OSPF_VL1
2.2.2.2           1   FULL/DR         00:00:38    12.12.12.2      FastEthernet0/0

RTR-A:

RTRA#sh ip ospf data
            OSPF Router with ID (1.1.1.1) (Process ID 1)
                Router Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         260         0x80000004 0x00618D 1
2.2.2.2         2.2.2.2         1     (DNA) 0x80000004 0x00A1DE 2
                Summary Net Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum
11.11.11.1      1.1.1.1         468         0x80000001 0x00DD38
12.12.12.0      1.1.1.1         468         0x80000001 0x000C02
12.12.12.0      2.2.2.2         616   (DNA) 0x80000002 0x00EB1D
                Router Link States (Area 1)
Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         468         0x80000003 0x00C044 1
                Summary Net Link States (Area 1)
Link ID         ADV Router      Age         Seq#       Checksum
12.12.12.0      1.1.1.1         468         0x80000001 0x000C02
22.22.22.22     1.1.1.1         257         0x80000001 0x00E1F3
                Router Link States (Area 2)
Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         261         0x80000005 0x003E8F 1
2.2.2.2         2.2.2.2         262         0x80000004 0x0002C3 1
                Net Link States (Area 2)
Link ID         ADV Router      Age         Seq#       Checksum
12.12.12.2      2.2.2.2         628         0x80000002 0x00FF02
                Summary Net Link States (Area 2)
Link ID         ADV Router      Age         Seq#       Checksum
11.11.11.1      1.1.1.1         469         0x80000001 0x00DD38
22.22.22.22     2.2.2.2         878         0x80000002 0x005D7D

RTR-B:

RTRB#sh ip route ospf
     11.0.0.0/32 is subnetted, 1 subnets
O IA    11.11.11.1 [110/11] via 12.12.12.1, 00:08:56, FastEthernet0/0

RTRB#sh ip ospf data
            OSPF Router with ID (2.2.2.2) (Process ID 1)
                Router Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         1     (DNA) 0x80000004 0x00618D 1
2.2.2.2         2.2.2.2         556         0x80000004 0x00A1DE 2
                Summary Net Link States (Area 0)
Link ID         ADV Router      Age         Seq#       Checksum
11.11.11.1      1.1.1.1         208   (DNA) 0x80000001 0x00DD38
12.12.12.0      1.1.1.1         208   (DNA) 0x80000001 0x000C02
12.12.12.0      2.2.2.2         1171        0x80000002 0x00EB1D
                Router Link States (Area 2)
Link ID         ADV Router      Age         Seq#       Checksum Link count
1.1.1.1         1.1.1.1         556         0x80000005 0x003E8F 1
2.2.2.2         2.2.2.2         556         0x80000004 0x0002C3 1
                Net Link States (Area 2)
Link ID         ADV Router      Age         Seq#       Checksum
12.12.12.2      2.2.2.2         921         0x80000002 0x00FF02
                Summary Net Link States (Area 2)
Link ID         ADV Router      Age         Seq#       Checksum
11.11.11.1      1.1.1.1         765         0x80000001 0x00DD38
22.22.22.22     2.2.2.2         1172        0x80000002 0x005D7D

Q & A time

- I can explain if you have any questions and thanks for reading :)