R3
interface FastEthernet0/1
ip address 172.16.1.3 255.255.255.0
duplex auto
speed auto
!
router ospf 1
log-adjacency-changes
network 3.3.3.3 0.0.0.0 area 0
network 172.16.1.0 0.0.0.255 area 17
network 192.168.3.0 0.0.0.255 area 0
R4
interface Loopback0
ip address 4.4.4.4 255.255.255.255
!
interface Loopback1
ip address 10.1.1.1 255.255.255.0
!
interface Loopback2
ip address 10.2.2.2 255.255.255.0
!
interface FastEthernet0/1
ip address 172.16.1.4 255.255.255.0
duplex auto
speed auto
!
router ospf 1
router-id 4.4.4.4
log-adjacency-changes
network 4.4.4.4 0.0.0.0 area 17
network 10.1.1.0 0.0.0.255 area 10
network 10.2.2.0 0.0.0.255 area 10
network 172.16.1.0 0.0.0.255 area 17
*correction on IP address between R3 and R4, don't use the diagram IP but follow the conf instead
check the connectivity between R4 and R2,
ping to R2 Loopback0 from R4
R4#p 2.2.2.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
!!!!!
work fine, so we can assume connection along the way(R4-R3-R1-R2) have no problem
now, from R2 ping to any R4 Loopback and interface
R2>p 172.16.1.4
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.1.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 44/67/88 ms
R2>p 10.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.1.1.1, timeout is 2 seconds:
..
Success rate is 0 percent (0/2)
why ping to R4 interface successful, but not to R4 Loopback
this is because R4 int fa0/1 is advertised to area 17, which is directly connected to area 0
R4 Loopback1 and 2 are advertised to area 10, where there is no direct connection to area 0
to solve this, we should create a virtual-link between area 10 and area 0
area 17 will be the 'bridge' to make sure area 10 can communicate to area 0
use this command , area ['bridge' area number] virtual-link [remote RID]
R4
R4(config)#router ospf 1
R4(config-router)#area 17 virtual-link 3.3.3.3
you should receive an error message on R3
*Mar 1 00:52:20.355: %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from backbone area must be virtual-link but not found from 172.16.1.4, FastEthernet0/1
*Mar 1 00:52:30.355: %OSPF-4-ERRRCV: Received invalid packet: mismatch area ID, from backbone area must be virtual-link but not found from 172.16.1.4, FastEthernet0/1
this is because we haven't configure any virtual-link on R3 yet to connect to R4
R3
R3(config-router)#area 17 virtual-link 4.4.4.4
R3(config-router)#
*Mar 1 00:57:28.275: %OSPF-5-ADJCHG: Process 1, Nbr 4.4.4.4 on OSPF_VL1 from LOADING to FULL, Loading Done
once you configure on R3, it'll form neighbor via virtual interface OSPF_VL1 with 4.4.4.4
R3#sh ip os
*Mar 1 01:00:37.795: %SYS-5-CONFIG_I: Configured from console by console ne
Neighbor ID Pri State Dead Time Address Interface
4.4.4.4 0 FULL/ - - 172.16.1.4 OSPF_VL1
1.1.1.1 1 FULL/DR 00:00:31 192.168.3.1 FastEthernet0/0
4.4.4.4 1 FULL/DR 00:00:35 172.16.1.4 FastEthernet0/1
there's more detail on show ip ospf virtual-link, try on R4
R4#sh ip os virtual-links
Virtual Link OSPF_VL0 to router 3.3.3.3 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 17, via interface FastEthernet0/1, Cost of using 1
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:08
Adjacency State FULL (Hello suppressed)
Index 1/1, retransmission queue length 0, number of retransmission 1
First 0x0(0)/0x0(0) Next 0x0(0)/0x0(0)
Last retransmission scan length is 1, maximum is 1
Last retransmission scan time is 0 msec, maximum is 0 msec
here we can see information about virtual link and transit area (the 'bridge')
to make sure area 10 now are really connected to area 0, check from R2, try show IP route ospf
R2>sh ip rou os
1.0.0.0/32 is subnetted, 1 subnets
O 1.1.1.1 [110/2] via 192.168.2.1, 00:09:06, FastEthernet0/0
3.0.0.0/32 is subnetted, 1 subnets
O 3.3.3.3 [110/3] via 192.168.2.1, 00:09:06, FastEthernet0/0
4.0.0.0/32 is subnetted, 1 subnets
O IA 4.4.4.4 [110/4] via 192.168.2.1, 00:09:06, FastEthernet0/0
172.16.0.0/24 is subnetted, 1 subnets
O IA 172.16.1.0 [110/3] via 192.168.2.1, 00:09:06, FastEthernet0/0
10.0.0.0/32 is subnetted, 2 subnets
O IA 10.2.2.2 [110/4] via 192.168.2.1, 00:09:06, FastEthernet0/0
O IA 10.1.1.1 [110/4] via 192.168.2.1, 00:09:06, FastEthernet0/0
O 192.168.3.0/24 [110/2] via 192.168.2.1, 00:09:06, FastEthernet0/0
now route from area 10 being advertise across the same OSPF instance, which mean our virtual-link are working fine now ;)
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