Configuration:
R1:
interface Loopback0
ip address 10.0.0.1 255.224.0.0
!
!
interface Loopback32
ip address 10.32.0.1 255.224.0.0
!
!
interface Loopback64
ip address 10.64.0.1 255.224.0.0
!
!
interface Loopback96
ip address 10.96.0.1 255.224.0.0
!
interface Serial1/0
bandwidth 128
ip address 192.168.1.1 255.255.255.252
serial restart-delay 0
clock rate 64000
router ospf 1
router-id 1.1.1.1
log-adjacency-changes
network 10.0.0.0 0.31.255.255 area 0
network 10.32.0.0 0.31.255.255 area 0
network 10.64.0.0 0.31.255.255 area 0
network 10.96.0.0 0.31.255.255 area 0
network 192.168.1.0 0.0.0.3 area 0
__________________________________________________________________________________
R2:
interface FastEthernet0/0ip address 5.5.5.1 255.255.255.0
ip ospf priority 10
duplex half
!
!
interface Serial1/0
bandwidth 128
ip address 192.168.1.2 255.255.255.224
serial restart-delay 0
!
router ospf 1
router-id 2.2.2.1
log-adjacency-changes
network 5.5.5.0 0.0.0.255 area 1
network 192.168.1.0 0.0.0.3 area 0
___________________________________________________________________________________
R3:
interface Loopback45ip address 45.45.45.1 255.255.255.0
!
!
interface Loopback46
ip address 45.45.46.1 255.255.255.0
!
!
interface Loopback47
ip address 45.45.47.1 255.255.255.0
!
!
interface FastEthernet0/0
ip address 5.5.5.2 255.255.255.0
ip ospf priority 0
duplex half
!
!
!
router ospf 1
router-id 3.3.3.1
log-adjacency-changes
network 5.5.5.0 0.0.0.255 area 1
network 45.45.45.0 0.0.0.0 area 1
network 45.45.46.0 0.0.0.0 area 1
network 45.45.47.0 0.0.0.0 area 1
!
__________________________________________________________________________________
R4:
interface Loopback28ip address 28.28.28.1 255.255.255.0
!
!
interface Loopback29
ip address 28.28.29.1 255.255.255.0
!
!
interface Loopback30
ip address 28.28.30.1 255.255.255.0
!
!
interface FastEthernet0/0
ip address 5.5.5.3 255.255.255.0
ip ospf priority 0
duplex half
!
!
interface Serial1/0
bandwidth 64
ip address 7.7.7.1 255.255.255.252
serial restart-delay 0
clock rate 64000
!
router ospf 1
router-id 4.4.4.1
log-adjacency-changes
network 5.5.5.0 0.0.0.255 area 1
network 7.7.7.0 0.0.0.3 area 51
router-id 4.4.4.1
log-adjacency-changes
network 5.5.5.0 0.0.0.255 area 1
network 7.7.7.0 0.0.0.3 area 51
___________________________________________________________________________________
R5:
interface Loopback31
ip address 31.31.31.1 255.255.255.0
!
!
interface Loopback32
ip address 31.31.32.1 255.255.255.0
!
interface Serial1/0
ip address 7.7.7.2 255.255.255.252
serial restart-delay 0
!
router ospf 1
router-id 5.5.5.1
log-adjacency-changes
network 7.7.7.0 0.0.0.3 area 51
network 31.31.31.0 0.0.0.255 area 51
network 31.31.32.0 0.0.0.255 area 51
___________________________________________________________________________________
Negiborship Verification
R1#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
2.2.2.1 0 FULL/ - 00:00:37 192.168.1.2 Serial1/0
___________________________________________________________________________________
Neighbor ID Pri State Dead Time Address Interface
1.1.1.1 0 FULL/ - 00:00:39 192.168.1.1 Serial1/0
3.3.3.1 0 FULL/DROTHER 00:00:36 5.5.5.2 FastEthernet0/0
4.4.4.1 0 FULL/DROTHER 00:00:33 5.5.5.3 FastEthernet0/0
___________________________________________________________________________________
R3#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
2.2.2.1 10 FULL/DR 00:00:31 5.5.5.1 FastEthernet0/0
4.4.4.1 0 2WAY/DROTHER 00:00:36 5.5.5.3 FastEthernet0/0
___________________________________________________________________________________
R4#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
2.2.2.1 10 FULL/DR 00:00:31 5.5.5.1 FastEthernet0/0
3.3.3.1 0 2WAY/DROTHER 00:00:37 5.5.5.2 FastEthernet0/0
5.5.5.1 0 FULL/ - 00:00:37 7.7.7.2 Serial1/0
___________________________________________________________________________________
R5#sh ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
4.4.4.1 0 FULL/ - 00:00:38 7.7.7.1 Serial1/0
____________________________________________________________________________________
Note: Lets take a look at what routers see as they become neighbors: The following output happens between R4 and R5.
R4#
*May 28 10:56:50.735: OSPF: Serial1/0: Route adjust notification: UP/UP
*May 28 10:56:50.735: OSPF: Interface Serial1/0 going Up
*May 28 10:56:50.739: OSPF: Serial1/0: Interface state change to UP, new ospf state P2P
*May 28 10:56:51.235: OSPF: Build router LSA for area 51, router ID 4.4.4.1, seq 0x80000008, process 1
R4#
*May 28 10:57:03.419: OSPF: Rcv DBD from 5.5.5.1 on Serial1/0 seq 0x1653 opt 0x52 flag 0x7 len 32 mtu 1500 state INIT
*May 28 10:57:03.419: OSPF: 2 Way Communication to 5.5.5.1 on Serial1/0, state 2WAY
*May 28 10:57:03.423: OSPF: Serial1/0 Nbr 5.5.5.1: Prepare dbase exchange
*May 28 10:57:03.423: OSPF: Send DBD to 5.5.5.1 on Serial1/0 seq 0x151D opt 0x52 flag 0x7 len 32
*May 28 10:57:03.423: OSPF: NBR Negotiation Done. We are the SLAVE
*May 28 10:57:03.423: OSPF: Serial1/0 Nbr 5.5.5.1: Summary list built, size 2
*May 28 10:57:03.427: OSPF: Send DBD to 5.5.5.1 on Serial1/0 seq 0x1653 opt 0x52 flag 0x2 len 72
*May 28 10:57:03.499: OSPF: Rcv DBD from 5.5.5.1 on Serial1/0 seq 0x1654 opt 0x52 flag 0x1 len 72 mtu 1500 state EXCHANGE
*May 28 10:57:03.503: OSPF: Exchange Done with 5.5.5.1 on Serial1/0
*May 28 10:57:03.503: OSPF: Send LS REQ to 5.5.5.1 length 12 LSA count 1
*May 28 10:57:03.503: OSPF: Send DBD to 5.5.5.1 on Serial1/0 seq 0x1654 opt 0x52 flag 0x0 len 32
*May 28 1
R4#0:57:03.595: OSPF: Rcv LS UPD from 5.5.5.1 on Serial1/0 length 76 LSA count 1
*May 28 10:57:03.595: OSPF: Synchronized with 5.5.5.1 on Serial1/0, state FULL
*May 28 10:57:03.599: %OSPF-5-ADJCHG: Process 1, Nbr 5.5.5.1 on Serial1/0 from LOADING to FULL, Loading Done
*May 28 10:57:03.651: OSPF: Rcv LS REQ from 5.5.5.1 on Serial1/0 length 36 LSA count 1
*May 28 10:57:04.099: OSPF: Build router LSA for area 51, router ID 4.4.4.1, seq 0x80000009, process 1
R4#U ALL
All possible debugging has been turned off
____________________________________________________________________________________
R5#
*May 28 10:58:58.183: OSPF: Serial1/0: Route adjust notification: UP/UP
*May 28 10:58:58.183: OSPF: Interface Serial1/0 going Up
*May 28 10:58:58.187: OSPF: Serial1/0: Interface state change to UP, new ospf state P2P
*May 28 10:58:58.215: OSPF: 2 Way Communication to 4.4.4.1 on Serial1/0, state 2WAY
*May 28 10:58:58.215: OSPF: Serial1/0 Nbr 4.4.4.1: Prepare dbase exchange
*May 28 10:58:58.215: OSPF: Send DBD to 4.4.4.1 on Serial1/0 seq 0x1653 opt 0x52 flag 0x7 len 32
*May 28 10:58:58.491: OSPF: Rcv DBD from 4.4.4.1 on Serial1/0 seq 0x151D opt 0x52 flag 0x7 len 32 mtu 1500 state EXSTART
*May 28 10:58:58.491: OSPF: First DBD and we are not SLAVE
*May 28 10:58:58.495: OSPF: Rcv DBD from 4.4.4.1 on Serial1/0 seq 0x1653 opt 0x52 flag 0x2 len 72 mtu 1500 state EXSTART
*May 28 10:58:58.495: OSPF: NBR Negotiation Done. We are the MASTER
*May 28 10:58:58.495: OSPF: Serial1/0 Nbr
R5#4.4.4.1: Summary list built, size 2
*May 28 10:58:58.495: OSPF: Send DBD to 4.4.4.1 on Serial1/0 seq 0x1654 opt 0x52 flag 0x1 len 72
*May 28 10:58:58.603: OSPF: Rcv LS REQ from 4.4.4.1 on Serial1/0 length 36 LSA count 1
*May 28 10:58:58.607: OSPF: Send UPD to 7.7.7.1 on Serial1/0 length 52 LSA count 1
*May 28 10:58:58.615: OSPF: Rcv DBD from 4.4.4.1 on Serial1/0 seq 0x1654 opt 0x52 flag 0x0 len 32 mtu 1500 state EXCHANGE
*May 28 10:58:58.615: OSPF: Exchange Done with 4.4.4.1 on Serial1/0
*May 28 10:58:58.619: OSPF: Send LS REQ to 4.4.4.1 length 12 LSA count 1
*May 28 10:58:58.683: OSPF: Build router LSA for area 51, router ID 5.5.5.1, seq 0x80000009, process 1
*May 28 10:58:58.747: OSPF: Rcv LS UPD from 4.4.4.1 on Serial1/0 length 64 LSA count 1
*May 28 10:58:58.751: OSPF: Synchronized with 4.4.4.1 on Serial1/0, state FULL
*May 28 10:58:58.751: %OSPF-5-ADJCHG: Process 1, Nbr 4.4.4.1 on Serial1/0 from LOADING to FULL, Loading Done
*May 28 10:58:58.751: OSPF: Serial1/0 Nbr 4
R5#.4.4.1: Clean-up dbase exchange
R5#
*May 28 10:59:03.683: OSPF: Build router LSA for area 51, router ID 5.5.5.1, seq 0x8000000A, process 1
R5#SH IP OSpf NEighbor
Neighbor ID Pri State Dead Time Address Interface
4.4.4.1 0 FULL/ - 00:00:38 7.7.7.1 Serial1/0
R5#U ALL
All possible debugging has been turned off
____________________________________________________________________________________
Let's take a look at the Link State Database of R2 and R5:
R2#SH IP OSpf Database
OSPF Router with ID (2.2.2.1) (Process ID 1)
Router Link States (Area 0)
Link ID ADV Router Age Seq# Checksum Link count
1.1.1.1 1.1.1.1 994 0x80000009 0x005099 6
2.2.2.1 2.2.2.1 641 0x80000003 0x0090A7 2
Summary Net Link States (Area 0)
Link ID ADV Router Age Seq# Checksum
5.5.5.0 2.2.2.1 641 0x80000002 0x00A67E
Router Link States (Area 1)
Link ID ADV Router Age Seq# Checksum Link count
2.2.2.1 2.2.2.1 396 0x80000003 0x00A75A 1
3.3.3.1 3.3.3.1 371 0x80000003 0x007685 1
4.4.4.1 4.4.4.1 91 0x80000003 0x0048AC 1
Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
5.5.5.1 2.2.2.1 138 0x80000003 0x0036C8
Summary Net Link States (Area 1)
Link ID ADV Router Age Seq# Checksum
10.0.0.1 2.2.2.1 644 0x80000002 0x006CAC
10.32.0.1 2.2.2.1 645 0x80000002 0x00EA0E
10.64.0.1 2.2.2.1 645 0x80000002 0x00696F
10.96.0.1 2.2.2.1 646 0x80000002 0x00E7D0
192.168.1.0 2.2.2.1 646 0x80000002 0x007762
192.168.1.3 2.2.2.1 646 0x80000002 0x009F0B
__________________________________________________________________________________
R5#sh ip ospf database
OSPF Router with ID (5.5.5.1) (Process ID 1)
Router Link States (Area 51)
Link ID ADV Router Age Seq# Checksum Link count
4.4.4.1 4.4.4.1 581 0x80000009 0x000882 2
5.5.5.1
____________________________________________________________________________________
Now for the Virtual Link configuration: Before I configure the virtual link let's take a look at the routing table of R1 and R4. Because the network is discontiguous R1 and R4 will not be able to communicate with each other.
R1#SH IP ROUTe ospf
Codes: L - local, 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, + - replicated route
Gateway of last resort is not set
5.0.0.0/24 is subnetted, 1 subnets
O IA 5.5.5.0 [110/782] via 192.168.1.2, 00:51:17, Serial1/0
192.168.1.0/24 is variably subnetted, 3 subnets, 3 masks
O 192.168.1.0/27 [110/1562] via 192.168.1.2, 00:57:56, Serial1/0
R1#ping 31.31.31.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 31.31.31.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
___________________________________________________________________________________R5#sh R5#sh ip route ospf
Codes: L - local, 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, + - replicated route
Gateway of last resort is not set
R5#ping 10.0.0.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.0.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R5#
Note: As we can see there is no end to end network connectivity. The routing tables of R1 and R5 give proof to this.
Note: Virtual Links are a last resort to a disjointed network, this is only a temporary fix
__________________________________________________________________________________
Virtual Link config
R2(config)#router ospf 1
R2(config-router)#area 1 virtual-link 4.4.4.1
*May 28 11:23:10.019: %OSPF-5-ADJCHG: Process 1, Nbr 4.4.4.1 on OSPF_VL1 from LOADING to FULL, Loading Done
__________________________________________________________________________________
R4(config-router)#area 1 virtual-link 2.2.2.1
R4(config-router)#
*May 28 11:23:10.019: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.1 on OSPF_VL1 from LOADING to FULL, Loading Done
___________________________________________________________________________________
Note: Let us quickly verify the status of the virtual link on R2 and R4, then I will revisit the routing table of R1 and R5.
R2#SH IP OSpf VIrtual-links
Virtual Link OSPF_VL0 to router 4.4.4.1 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface FastEthernet0/0
Topology-MTID Cost Disabled Shutdown Topology Name
0 1 no no Base
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Adjacency State FULL (Hello suppressed)
Index 2/4, 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
_________________________________________________________________________________
R4#SH IP OSpf VIrtual-links
Virtual Link OSPF_VL1 to router 2.2.2.1 is up
Run as demand circuit
DoNotAge LSA allowed.
Transit area 1, via interface FastEthernet0/0
Topology-MTID Cost Disabled Shutdown Topology Name
0 1 no no Base
Transmit Delay is 1 sec, State POINT_TO_POINT,
Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5
Hello due in 00:00:02
Adjacency State FULL (Hello suppressed)
Index 1/3, 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
R1 and R2 routing table verification:
R1#sh ip route ospf
Codes: L - local, 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, + - replicated route
Gateway of last resort is not set
5.0.0.0/24 is subnetted, 1 subnets
O IA 5.5.5.0 [110/782] via 192.168.1.2, 01:06:15, Serial1/0
7.0.0.0/30 is subnetted, 1 subnets
O IA 7.7.7.0 [110/2344] via 192.168.1.2, 00:06:32, Serial1/0
31.0.0.0/32 is subnetted, 2 subnets
O IA 31.31.31.1 [110/2345] via 192.168.1.2, 00:06:32, Serial1/0
O IA 31.31.32.1 [110/2345] via 192.168.1.2, 00:06:32, Serial1/0
192.168.1.0/24 is variably subnetted, 3 subnets, 3 masks
O 192.168.1.0/27 [110/1562] via 192.168.1.2, 01:12:54, Serial1/0
R1#ping 31.31.31.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 31.31.31.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 108/135/192 ms
___________________________________________________________________________________
R5#sh ip route ospf
Codes: L - local, 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, + - replicated route
Gateway of last resort is not set
5.0.0.0/24 is subnetted, 1 subnets
O IA 5.5.5.0 [110/65] via 7.7.7.1, 00:08:19, Serial1/0
10.0.0.0/32 is subnetted, 4 subnets
O IA 10.0.0.1 [110/847] via 7.7.7.1, 00:08:15, Serial1/0
O IA 10.32.0.1 [110/847] via 7.7.7.1, 00:08:15, Serial1/0
O IA 10.64.0.1 [110/847] via 7.7.7.1, 00:08:15, Serial1/0
O IA 10.96.0.1 [110/847] via 7.7.7.1, 00:08:15, Serial1/0
192.168.1.0/24 is variably subnetted, 2 subnets, 2 masks
O IA 192.168.1.0/27 [110/846] via 7.7.7.1, 00:08:15, Serial1/0
O IA 192.168.1.0/30 [110/1627] via 7.7.7.1, 00:08:15, Serial1/0
R5#ping 10.0.0.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 112/151/188 ms
R5#ping 10.32.0.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.32.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 112/148/188 ms
R5#ping 10.64.0.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.64.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 108/143/176 ms
R5#ping 10.96.0.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.96.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 120/142/188 ms
We now have full network reachability
