Configuring OSPF Virtual Links

Configuring an OSPF virtual link requires a minor amount of configuration just to get the link working, with several optional configuration items. Most of the optional configuration settings relate to features that would normally be configured on the interface connecting two neighboring routers, but with a virtual link, there is no such interface, so the parameters must be added to the area virtual-link command.

The following list summarizes the key configuration options on the area virtual-link router sub-command:

• The remote-RID in the area <area-num> virtual-link <remote-RID> command refers to the other router’s RID.

• The area-num in the area <area-num> virtual-link <remote-RID> command refers to the transit area over which the packets flow between the two routers.

• The transit area over which the two routers communicate must not be a stubby area.

• The optional configuration of OSPF neighbor authentication parameters, normally configured as interface sub-commands, must be configured as additional parameters on the area virtual-link command.

• The optional configuration of Hello and Dead intervals, normally configured as interface sub-commands, must be configured as additional parameters on the area virtual-link command.

The router assigns the virtual link an OSPF cost as if it were a point-to-point link. The router calculates the cost as the cost to reach the router on the other end of the link, as calculated using the transit area’s LSDB.

R1#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#interface loop 1

R1(config-if)#

*Jun 27 14:51:46.727: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback1, changed state to up

R1(config-if)#ip address 10.1.1.1 255.255.255.0

R1(config-if)#

R1(config-if)#interface loop 30

R1(config-if)#

*Jun 27 14:52:08.563: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback30, changed state to up

R1(config-if)#ip address 172.30.30.1 255.255.255.252

R1(config-if)#

R1(config-if)#interface serial 2/0

R1(config-if)#ip address 10.1.12.1 255.255.255.0

R1(config-if)#no shut

R1(config-if)#end

*Jun 27 14:52:42.415: %LINK-3-UPDOWN: Interface Serial2/0, changed state to up

*Jun 27 14:52:43.423: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial2/0, changed state to up

R1(config-if)#end

R1#

R2#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R2(config)#interface loop 2

R2(config-if)#

*Jun 27 14:51:44.047: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback2, changed state to up

R2(config-if)#ip address 10.1.2.1 255.255.255.0

R2(config-if)#

R2(config-if)#interface serial 2/0

R2(config-if)#ip address 10.1.12.2 255.255.255.0

R2(config-if)#no shut

R2(config-if)#

*Jun 27 14:52:24.603: %LINK-3-UPDOWN: Interface Serial2/0, changed state to up

R2(config-if)#

*Jun 27 14:52:25.611: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial2/0, changed state to up

R2(config-if)#do ping 10.1.12.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.1.12.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 12/18/28 ms

R2(config-if)#

R2(config-if)#interface serial 2/1

R2(config-if)#ip address 10.1.23.2 255.255.255.0

R2(config-if)#no shut

R2(config-if)#

*Jun 27 14:52:50.275: %LINK-3-UPDOWN: Interface Serial2/1, changed state to up

R2(config-if)#

*Jun 27 14:52:51.283: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial2/1, changed state to up

R2(config-if)#end

R2#

R3#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R3(config)#interface loop 3

R3(config-if)#

*Jun 27 14:53:26.583: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback3, changed state to up

R3(config-if)#ip address 10.1.3.1 255.255.255.0

R3(config-if)#

R3(config-if)#interface loop 100

R3(config-if)#

*Jun 27 14:53:48.847: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback100, changed state to up

R3(config-if)#ip address 192.168.100.1 255.255.255.0

R3(config-if)#

R3(config-if)#interface loop 101                   

R3(config-if)#

*Jun 27 14:54:07.119: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback101, changed state to up

R3(config-if)#ip address 192.168.101.1 255.255.255.0

R3(config-if)#

R3(config-if)#interface loop 102                   

R3(config-if)#

*Jun 27 14:54:19.403: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback102, changed state to up

R3(config-if)#ip address 192.168.102.1 255.255.255.0

R3(config-if)#

R3(config-if)#interface loop 103                   

R3(config-if)#

*Jun 27 14:54:33.855: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback103, changed state to up

R3(config-if)#ip address 192.168.103.1 255.255.255.0

R3(config-if)#

R3(config-if)#interface serial 2/1

R3(config-if)#ip address 10.1.23.3 255.255.255.0

R3(config-if)#no shut

R3(config-if)#

*Jun 27 14:54:55.175: %LINK-3-UPDOWN: Interface Serial2/1, changed state to up

R3(config-if)#

*Jun 27 14:54:56.183: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial2/1, changed state to up

R3(config-if)#do ping 10.1.23.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.1.23.2, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 20/23/28 ms

R1#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#router ospf 1

R1(config-router)#router-id 1.1.1.1

R1(config-router)#network 10.1.12.0 0.0.0.255 area 0

R1(config-router)#network 10.1.1.0 0.0.0.255 area 0

R1(config-router)#interface loop 1

R1(config-if)#ip ospf network ?

  broadcast            Specify OSPF broadcast multi-access network

  non-broadcast        Specify OSPF NBMA network

  point-to-multipoint  Specify OSPF point-to-multipoint network

  point-to-point       Specify OSPF point-to-point network

R1(config-if)#ip ospf network point-to-point      // DEFAULT LOOPBACK INTERFACE BEHAVIOR IN OSPF IS TO ADVERTISE A /32 HOST ROUTE; NEED TO ADVERTISE AS /24 IN OSPF

R1(config-if)#end

R1#

*Jun 27 15:08:39.371: %SYS-5-CONFIG_I: Configured from console by console

R1#

R1#show ip ospf      // COMMAND TO VERIFY OSPF ROUTER ID; ISSUE A clear ip ospf <PROCESS ID> AFTER MAKING CHANGES

 Routing Process "ospf 1" with ID 1.1.1.1

 Start time: 00:23:21.372, Time elapsed: 00:00:48.992

 Supports only single TOS(TOS0) routes

 Supports opaque LSA

 Supports Link-local Signaling (LLS)

 Supports area transit capability

 Supports NSSA (compatible with RFC 3101)

 Event-log enabled, Maximum number of events: 1000, Mode: cyclic

 Router is not originating router-LSAs with maximum metric

 Initial SPF schedule delay 5000 msecs

 Minimum hold time between two consecutive SPFs 10000 msecs

 Maximum wait time between two consecutive SPFs 10000 msecs

 Incremental-SPF disabled

 Minimum LSA interval 5 secs

 Minimum LSA arrival 1000 msecs

 LSA group pacing timer 240 secs

 Interface flood pacing timer 33 msecs

 Retransmission pacing timer 66 msecs

 Number of external LSA 0. Checksum Sum 0x000000

 Number of opaque AS LSA 0. Checksum Sum 0x000000

 Number of DCbitless external and opaque AS LSA 0

 Number of DoNotAge external and opaque AS LSA 0

 Number of areas in this router is 1. 1 normal 0 stub 0 nssa

 Number of areas transit capable is 0

 External flood list length 0

 IETF NSF helper support enabled

 Cisco NSF helper support enabled

 Reference bandwidth unit is 100 mbps

    Area BACKBONE(0) (Inactive)

        Number of interfaces in this area is 2 (1 loopback)

        Area has no authentication

        SPF algorithm last executed 00:00:03.692 ago

        SPF algorithm executed 3 times

        Area ranges are

        Number of LSA 1. Checksum Sum 0x00C8EB

        Number of opaque link LSA 0. Checksum Sum 0x000000

        Number of DCbitless LSA 0

        Number of indication LSA 0

        Number of DoNotAge LSA 0

        Flood list length 0

R2#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R2(config)#router ospf 1

R2(config-router)#router-id 2.2.2.2

R2(config-router)#network 10.1.12.0 0.0.0.255 area 0

R2(config-router)#

*Jun 27 15:08:51.767: %OSPF-5-ADJCHG: Process 1, Nbr 1.1.1.1 on Serial2/0 from LOADING to FULL, Loading Done

R2(config-router)#network 10.1.2.0 0.0.0.255 area 0

R2(config-router)#interface loop 2

R2(config-if)#ip ospf network point-to-point

R2(config-if)#end

R2#

*Jun 27 15:09:26.903: %SYS-5-CONFIG_I: Configured from console by console

R2#show ip ospf

 Routing Process "ospf 1" with ID 2.2.2.2

 Start time: 00:22:45.484, Time elapsed: 00:00:54.216

 Supports only single TOS(TOS0) routes

 Supports opaque LSA

 Supports Link-local Signaling (LLS)

 Supports area transit capability

 Supports NSSA (compatible with RFC 3101)

 Event-log enabled, Maximum number of events: 1000, Mode: cyclic

 Router is not originating router-LSAs with maximum metric

 Initial SPF schedule delay 5000 msecs

 Minimum hold time between two consecutive SPFs 10000 msecs

 Maximum wait time between two consecutive SPFs 10000 msecs

 Incremental-SPF disabled

 Minimum LSA interval 5 secs

 Minimum LSA arrival 1000 msecs

 LSA group pacing timer 240 secs

 Interface flood pacing timer 33 msecs

 Retransmission pacing timer 66 msecs

 Number of external LSA 0. Checksum Sum 0x000000

 Number of opaque AS LSA 0. Checksum Sum 0x000000

 Number of DCbitless external and opaque AS LSA 0

 Number of DoNotAge external and opaque AS LSA 0

 Number of areas in this router is 1. 1 normal 0 stub 0 nssa

 Number of areas transit capable is 0

 External flood list length 0

 IETF NSF helper support enabled

 Cisco NSF helper support enabled

 Reference bandwidth unit is 100 mbps

    Area BACKBONE(0)

        Number of interfaces in this area is 2 (1 loopback)

        Area has no authentication

        SPF algorithm last executed 00:00:05.212 ago

        SPF algorithm executed 3 times

        Area ranges are

        Number of LSA 2. Checksum Sum 0x00E3A1

        Number of opaque link LSA 0. Checksum Sum 0x000000

        Number of DCbitless LSA 0

        Number of indication LSA 0

        Number of DoNotAge LSA 0

        Flood list length 0

*Jun 27 15:10:41.635: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial2/0 from LOADING to FULL, Loading Done

R1#

R1#show ip ospf neighbor     // VERIFY OSPF NEIGHBOR

Neighbor ID     Pri   State           Dead Time   Address         Interface

2.2.2.2           0   FULL/  -        00:00:37    10.1.12.2       Serial2/0

R1#

R1#show ip route

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, H - NHRP, l - LISP

       + - replicated route, % - next hop override

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 5 subnets, 2 masks

C        10.1.1.0/24 is directly connected, Loopback1

L        10.1.1.1/32 is directly connected, Loopback1

O        10.1.2.0/24 [110/65] via 10.1.12.2, 00:00:54, Serial2/0

C        10.1.12.0/24 is directly connected, Serial2/0

L        10.1.12.1/32 is directly connected, Serial2/0

      172.30.0.0/16 is variably subnetted, 2 subnets, 2 masks

C        172.30.30.0/30 is directly connected, Loopback30

L        172.30.30.1/32 is directly connected, Loopback30

R2#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface

1.1.1.1           0   FULL/  -        00:00:31    10.1.12.1       Serial2/0

R2#

R2#show ip route

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, H - NHRP, l - LISP

       + - replicated route, % - next hop override

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 7 subnets, 2 masks

O        10.1.1.0/24 [110/65] via 10.1.12.1, 00:02:08, Serial2/0

C        10.1.2.0/24 is directly connected, Loopback2

L        10.1.2.1/32 is directly connected, Loopback2

C        10.1.12.0/24 is directly connected, Serial2/0

L        10.1.12.2/32 is directly connected, Serial2/0

C        10.1.23.0/24 is directly connected, Serial2/1

L        10.1.23.2/32 is directly connected, Serial2/1

R2#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R2(config)#router ospf 1

R2(config-router)#network 10.1.23.0 0.0.0.255 area 23

R3#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R3(config)#router ospf 1

R3(config-router)#router-id 3.3.3.3

R3(config-router)#network 10.1.23.0 0.0.0.255 area 23

R3(config-router)#

*Jun 27 15:12:31.823: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on Serial2/1 from LOADING to FULL, Loading Done

R3(config-router)#network 10.1.3.0 0.0.0.255 area 23

R3(config-router)#

R3(config-router)#interface loop 3

R3(config-if)#ip ospf network point-to-point

R3(config-if)#end

R3#

*Jun 27 15:13:05.111: %SYS-5-CONFIG_I: Configured from console by console

R3#show ip ospf

 Routing Process "ospf 1" with ID 3.3.3.3

 Start time: 00:26:02.648, Time elapsed: 00:00:49.976

 Supports only single TOS(TOS0) routes

 Supports opaque LSA

 Supports Link-local Signaling (LLS)

 Supports area transit capability

 Supports NSSA (compatible with RFC 3101)

 Event-log enabled, Maximum number of events: 1000, Mode: cyclic

 Router is not originating router-LSAs with maximum metric

 Initial SPF schedule delay 5000 msecs

 Minimum hold time between two consecutive SPFs 10000 msecs

 Maximum wait time between two consecutive SPFs 10000 msecs

 Incremental-SPF disabled

 Minimum LSA interval 5 secs

 Minimum LSA arrival 1000 msecs

 LSA group pacing timer 240 secs

 Interface flood pacing timer 33 msecs

 Retransmission pacing timer 66 msecs

 Number of external LSA 0. Checksum Sum 0x000000

 Number of opaque AS LSA 0. Checksum Sum 0x000000

 Number of DCbitless external and opaque AS LSA 0

 Number of DoNotAge external and opaque AS LSA 0

 Number of areas in this router is 1. 1 normal 0 stub 0 nssa

 Number of areas transit capable is 0

 External flood list length 0

 IETF NSF helper support enabled

 Cisco NSF helper support enabled

 Reference bandwidth unit is 100 mbps

    Area 23

        Number of interfaces in this area is 2 (1 loopback)

        Area has no authentication

        SPF algorithm last executed 00:00:07.688 ago

        SPF algorithm executed 3 times

        Area ranges are

        Number of LSA 5. Checksum Sum 0x031D29

        Number of opaque link LSA 0. Checksum Sum 0x000000

        Number of DCbitless LSA 0

        Number of indication LSA 0

        Number of DoNotAge LSA 0

        Flood list length 0

R2#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface

1.1.1.1           0   FULL/  -        00:00:38    10.1.12.1       Serial2/0

3.3.3.3           0   FULL/  -        00:00:34    10.1.23.3       Serial2/1

R3#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R3(config)#router ospf 1

R3(config-router)#network 192.168.100.0 0.0.3.255 area 100

R3(config-router)#interface loop 100

R3(config-if)#ip ospf network point-to-point

R3(config-if)#interface loop 101           

R3(config-if)#ip ospf network point-to-point

R3(config-if)#interface loop 102           

R3(config-if)#ip ospf network point-to-point

R3(config-if)#interface loop 103           

R3(config-if)#ip ospf network point-to-point

R2#show ip route      // CAN'T SEE ROUTES IN R3 AREA 100 SINCE IT'S NOT CONNECTED TO A BACKBONE AREA 0

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, H - NHRP, l - LISP

       + - replicated route, % - next hop override

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks

O        10.1.1.0/24 [110/65] via 10.1.12.1, 00:03:57, Serial2/0

C        10.1.2.0/24 is directly connected, Loopback2

L        10.1.2.1/32 is directly connected, Loopback2

O        10.1.3.0/24 [110/65] via 10.1.23.3, 00:02:51, Serial2/1

C        10.1.12.0/24 is directly connected, Serial2/0

L        10.1.12.2/32 is directly connected, Serial2/0

C        10.1.23.0/24 is directly connected, Serial2/1

L        10.1.23.2/32 is directly connected, Serial2/1

R2#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R2(config)#router ospf 1

R2(config-router)#area ?

  <0-4294967295>  OSPF area ID as a decimal value

  A.B.C.D         OSPF area ID in IP address format

R2(config-router)#area 23 ?

  authentication  Enable authentication

  capability      Enable area specific capability

  default-cost    Set the summary default-cost of a NSSA/stub area

  filter-list     Filter networks between OSPF areas

  nssa            Specify a NSSA area

  range           Summarize routes matching address/mask (border routers only)

  sham-link       Define a sham link and its parameters

  stub            Specify a stub area

  virtual-link    Define a virtual link and its parameters

R2(config-router)#area 23 virtual-link ?

  A.B.C.D  ID (IP addr) associated with virtual link neighbor

R2(config-router)#area 23 virtual-link 3.3.3.3      // OSPF VIRTUAL LINK IS A WORK AROUND SOLUTION TO CONNECT A DISCONTIGUOUS AREA TO BACKBONE AREA 0

*Jun 27 15:17:36.575: %OSPF-5-ADJCHG: Process 1, Nbr 3.3.3.3 on OSPF_VL0 from LOADING to FULL, Loading Done

R3#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R3(config)#router ospf 1

R3(config-router)#area 23 virtual-link 2.2.2.2

R3(config-router)#

*Jun 27 15:17:46.371: %OSPF-5-ADJCHG: Process 1, Nbr 2.2.2.2 on OSPF_VL0 from LOADING to FULL, Loading Done

R2#show ip route     // CAN NOW SEE ROUTES IN R3 AREA 100

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, H - NHRP, l - LISP

       + - replicated route, % - next hop override

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks

O        10.1.1.0/24 [110/65] via 10.1.12.1, 00:06:27, Serial2/0

C        10.1.2.0/24 is directly connected, Loopback2

L        10.1.2.1/32 is directly connected, Loopback2

O        10.1.3.0/24 [110/65] via 10.1.23.3, 00:05:21, Serial2/1

C        10.1.12.0/24 is directly connected, Serial2/0

L        10.1.12.2/32 is directly connected, Serial2/0

C        10.1.23.0/24 is directly connected, Serial2/1

L        10.1.23.2/32 is directly connected, Serial2/1

O IA  192.168.100.0/24 [110/65] via 10.1.23.3, 00:00:31, Serial2/1

O IA  192.168.101.0/24 [110/65] via 10.1.23.3, 00:00:31, Serial2/1

O IA  192.168.102.0/24 [110/65] via 10.1.23.3, 00:00:31, Serial2/1

O IA  192.168.103.0/24 [110/65] via 10.1.23.3, 00:00:31, Serial2/1

R2#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface

3.3.3.3           0   FULL/  -           -        10.1.23.3       OSPF_VL0

1.1.1.1           0   FULL/  -        00:00:32    10.1.12.1       Serial2/0

3.3.3.3           0   FULL/  -        00:00:39    10.1.23.3       Serial2/1

R2#show ip ospf interface

OSPF_VL0 is up, line protocol is up

  Internet Address 10.1.23.2/24, Area 0, Attached via Not Attached

  Process ID 1, Router ID 2.2.2.2, Network Type VIRTUAL_LINK, Cost: 64

  Topology-MTID    Cost    Disabled    Shutdown      Topology Name

        0           64        no          no            Base

  Configured as demand circuit

  Run as demand circuit

  DoNotAge LSA allowed

  Transmit Delay is 1 sec, State POINT_TO_POINT

  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

    oob-resync timeout 40

    Hello due in 00:00:06

  Supports Link-local Signaling (LLS)

  Cisco NSF helper support enabled

  IETF NSF helper support enabled

  Index 3/4, flood queue length 0

  Next 0x0(0)/0x0(0)

  Last flood scan length is 1, maximum is 1

  Last flood scan time is 0 msec, maximum is 0 msec

  Neighbor Count is 1, Adjacent neighbor count is 1

    Adjacent with neighbor 3.3.3.3  (Hello suppressed)

  Suppress hello for 1 neighbor(s)

Loopback2 is up, line protocol is up

  Internet Address 10.1.2.1/24, Area 0, Attached via Network Statement

  Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 1

  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

    oob-resync timeout 40

  Supports Link-local Signaling (LLS)

  Cisco NSF helper support enabled

  IETF NSF helper support enabled

  Index 2/2, flood queue length 0

  Next 0x0(0)/0x0(0)

  Last flood scan length is 0, maximum is 0

  Last flood scan time is 0 msec, maximum is 0 msec

  Neighbor Count is 0, Adjacent neighbor count is 0

  Suppress hello for 0 neighbor(s)

Serial2/0 is up, line protocol is up

  Internet Address 10.1.12.2/24, Area 0, Attached via Network Statement

  Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64

  Topology-MTID    Cost    Disabled    Shutdown      Topology Name

        0           64        no          no            Base

  Transmit Delay is 1 sec, State POINT_TO_POINT

  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

    oob-resync timeout 40

    Hello due in 00:00:06

  Supports Link-local Signaling (LLS)

  Cisco NSF helper support enabled

  IETF NSF helper support enabled

  Index 1/1, flood queue length 0

  Next 0x0(0)/0x0(0)

  Last flood scan length is 1, maximum is 6

  Last flood scan time is 0 msec, maximum is 4 msec

  Neighbor Count is 1, Adjacent neighbor count is 1

    Adjacent with neighbor 1.1.1.1

  Suppress hello for 0 neighbor(s)

Serial2/1 is up, line protocol is up

  Internet Address 10.1.23.2/24, Area 23, Attached via Network Statement

  Process ID 1, Router ID 2.2.2.2, Network Type POINT_TO_POINT, Cost: 64

  Topology-MTID    Cost    Disabled    Shutdown      Topology Name

        0           64        no          no            Base

  Transmit Delay is 1 sec, State POINT_TO_POINT

  Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

    oob-resync timeout 40

    Hello due in 00:00:07

  Supports Link-local Signaling (LLS)

  Cisco NSF helper support enabled

  IETF NSF helper support enabled

  Index 1/3, flood queue length 0

  Next 0x0(0)/0x0(0)

  Last flood scan length is 1, maximum is 1

  Last flood scan time is 0 msec, maximum is 0 msec

  Neighbor Count is 1, Adjacent neighbor count is 1

    Adjacent with neighbor 3.3.3.3

  Suppress hello for 0 neighbor(s)

R3#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R3(config)#router ospf 1

R3(config-router)#area 100 ?

  authentication  Enable authentication

  capability      Enable area specific capability

  default-cost    Set the summary default-cost of a NSSA/stub area

  filter-list     Filter networks between OSPF areas

  nssa            Specify a NSSA area

  range           Summarize routes matching address/mask (border routers only)

  sham-link       Define a sham link and its parameters

  stub            Specify a stub area

  virtual-link    Define a virtual link and its parameters

R3(config-router)#area 100 range ?

  A.B.C.D  IP address to match

R3(config-router)#area 100 range 192.168.100.0 255.255.252.0     // SUMMARIZE A SUPERNET ROUTE IN OSPF

R2#show ip route                 

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, H - NHRP, l - LISP

       + - replicated route, % - next hop override

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks

O        10.1.1.0/24 [110/65] via 10.1.12.1, 00:09:13, Serial2/0

C        10.1.2.0/24 is directly connected, Loopback2

L        10.1.2.1/32 is directly connected, Loopback2

O        10.1.3.0/24 [110/65] via 10.1.23.3, 00:08:07, Serial2/1

C        10.1.12.0/24 is directly connected, Serial2/0

L        10.1.12.2/32 is directly connected, Serial2/0

C        10.1.23.0/24 is directly connected, Serial2/1

L        10.1.23.2/32 is directly connected, Serial2/1

O IA  192.168.100.0/22 [110/65] via 10.1.23.3, 00:00:16, Serial2/1

R2#show ip ospf database

            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         754         0x80000004 0x00AE96 3

2.2.2.2         2.2.2.2         229         0x80000005 0x00B10A 4

3.3.3.3         3.3.3.3         1     (DNA) 0x80000002 0x00ADFC 1

                Summary Net Link States (Area 0)

Link ID         ADV Router      Age         Seq#       Checksum

10.1.3.0        2.2.2.2         514         0x80000001 0x002ABB

10.1.3.0        3.3.3.3         6     (DNA) 0x80000001 0x008998

10.1.23.0       2.2.2.2         570         0x80000001 0x00438F

10.1.23.0       3.3.3.3         6     (DNA) 0x80000001 0x0025A9

192.168.100.0   3.3.3.3         1     (DNA) 0x80000002 0x00263E

                Router Link States (Area 23)

Link ID         ADV Router      Age         Seq#       Checksum Link count

2.2.2.2         2.2.2.2         228         0x80000003 0x0099A1 2

3.3.3.3         3.3.3.3         229         0x80000005 0x00E92B 3

                Summary Net Link States (Area 23)

Link ID         ADV Router      Age         Seq#       Checksum

10.1.1.0        2.2.2.2         580         0x80000001 0x0040A7

10.1.2.0        2.2.2.2         580         0x80000001 0x00B274

10.1.12.0       2.2.2.2         580         0x80000001 0x00BC21

192.168.100.0   3.3.3.3         49          0x80000002 0x00263E

R3#show ip route

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, H - NHRP, l - LISP

       + - replicated route, % - next hop override

Gateway of last resort is not set

      10.0.0.0/8 is variably subnetted, 7 subnets, 2 masks

O        10.1.1.0/24 [110/129] via 10.1.23.2, 00:01:45, Serial2/1

O        10.1.2.0/24 [110/65] via 10.1.23.2, 00:01:45, Serial2/1

C        10.1.3.0/24 is directly connected, Loopback3

L        10.1.3.1/32 is directly connected, Loopback3

O        10.1.12.0/24 [110/128] via 10.1.23.2, 00:01:45, Serial2/1

C        10.1.23.0/24 is directly connected, Serial2/1

L        10.1.23.3/32 is directly connected, Serial2/1

O     192.168.100.0/22 is a summary, 00:01:45, Null0  // AN OSPF SUMMARY ROUTE CREATED A NULL0 OR ROUTE TO A BIT BUCKET WHICH DROPS TRAFFIC NOT COVERED BY THE SUMMARY ROUTE

      192.168.100.0/24 is variably subnetted, 2 subnets, 2 masks

C        192.168.100.0/24 is directly connected, Loopback100

L        192.168.100.1/32 is directly connected, Loopback100

      192.168.101.0/24 is variably subnetted, 2 subnets, 2 masks

C        192.168.101.0/24 is directly connected, Loopback101

L        192.168.101.1/32 is directly connected, Loopback101

      192.168.102.0/24 is variably subnetted, 2 subnets, 2 masks

C        192.168.102.0/24 is directly connected, Loopback102

L        192.168.102.1/32 is directly connected, Loopback102

      192.168.103.0/24 is variably subnetted, 2 subnets, 2 masks

C        192.168.103.0/24 is directly connected, Loopback103

L        192.168.103.1/32 is directly connected, Loopback103

R1#conf t

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#router ospf 1

R1(config-router)#?      

Router configuration commands:

  address-family         Enter Address Family command mode

  area                   OSPF area parameters

  auto-cost              Calculate OSPF interface cost according to bandwidth

  bfd                    BFD configuration commands

  capability             Enable specific OSPF feature

  compatible             OSPF compatibility list

  default                Set a command to its defaults

  default-information    Control distribution of default information

  default-metric         Set metric of redistributed routes

  discard-route          Enable or disable discard-route installation

  distance               Define an administrative distance

  distribute-list        Filter networks in routing updates

  domain-id              OSPF domain-id

  domain-tag             OSPF domain-tag

  event-log              OSPF Event Logging

  exit                   Exit from routing protocol configuration mode

  help                   Description of the interactive help system

  ignore                 Do not complain about specific event

  interface-id           Source of the interface ID

  ispf                   Enable incremental SPF computation

  limit                  Limit a specific OSPF feature

  local-rib-criteria     Enable or disable usage of local RIB as route criteria

  log-adjacency-changes  Log changes in adjacency state

  max-lsa                maximum number of LSAs OSPF process will receive

  max-metric             Set maximum metric

  maximum-paths          Forward packets over multiple paths

  mpls                   Configure MPLS routing protocol parameters

  neighbor               Specify a neighbor router

  network                Enable routing on an IP network

  no                     Negate a command or set its defaults

  nsf                    Non-stop forwarding

  passive-interface      Suppress routing updates on an interface

  prefix-suppression     OSPF prefix suppression

  priority               OSPF topology priority

  queue-depth            OSPF Hello/Router process queue depth

  redistribute           Redistribute information from another routing protocol

  router-id              router-id for this OSPF process

  shutdown               Shutdown the OSPF protocol under the current instance

  snmp                   Modify snmp parameters

  summary-address        Configure IP address summaries

  timers                 Adjust routing timers

  traffic-share          How to compute traffic share over alternate paths

  ttl-security           TTL security check

R1(config-router)#default-information ?

  originate  Distribute a default route

R1(config-router)#default-information originate ?

  always       Always advertise default route

  metric       OSPF default metric

  metric-type  OSPF metric type for default routes

  route-map    Route-map reference

  <cr>

R1(config-router)#default-information originate always    // GENERATES AND ADVERTISE A DEFAULT ROUTE IN OSPF; THE always KEYWORD WILL GENERATE A DEFAULT ROUTE EVEN IF NONE EXIST IN THE ROUTING TABLE

R2#show ip route       

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, H - NHRP, l - LISP

       + - replicated route, % - next hop override

Gateway of last resort is 10.1.12.1 to network 0.0.0.0

O*E2  0.0.0.0/0 [110/1] via 10.1.12.1, 00:00:17, Serial2/0

      10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks

O        10.1.1.0/24 [110/65] via 10.1.12.1, 00:12:21, Serial2/0

C        10.1.2.0/24 is directly connected, Loopback2

L        10.1.2.1/32 is directly connected, Loopback2

O        10.1.3.0/24 [110/65] via 10.1.23.3, 00:11:15, Serial2/1

C        10.1.12.0/24 is directly connected, Serial2/0

L        10.1.12.2/32 is directly connected, Serial2/0

C        10.1.23.0/24 is directly connected, Serial2/1

L        10.1.23.2/32 is directly connected, Serial2/1

O IA  192.168.100.0/22 [110/65] via 10.1.23.3, 00:03:24, Serial2/1

R2#ping 172.30.30.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.30.30.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 16/17/20 ms

R3#show ip route

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, H - NHRP, l - LISP

       + - replicated route, % - next hop override

Gateway of last resort is 10.1.23.2 to network 0.0.0.0

O*E2  0.0.0.0/0 [110/1] via 10.1.23.2, 00:00:38, Serial2/1

      10.0.0.0/8 is variably subnetted, 7 subnets, 2 masks

O        10.1.1.0/24 [110/129] via 10.1.23.2, 00:03:50, Serial2/1

O        10.1.2.0/24 [110/65] via 10.1.23.2, 00:03:50, Serial2/1

C        10.1.3.0/24 is directly connected, Loopback3

L        10.1.3.1/32 is directly connected, Loopback3

O        10.1.12.0/24 [110/128] via 10.1.23.2, 00:03:50, Serial2/1

C        10.1.23.0/24 is directly connected, Serial2/1

L        10.1.23.3/32 is directly connected, Serial2/1

O     192.168.100.0/22 is a summary, 00:03:50, Null0

      192.168.100.0/24 is variably subnetted, 2 subnets, 2 masks

C        192.168.100.0/24 is directly connected, Loopback100

L        192.168.100.1/32 is directly connected, Loopback100

      192.168.101.0/24 is variably subnetted, 2 subnets, 2 masks

C        192.168.101.0/24 is directly connected, Loopback101

L        192.168.101.1/32 is directly connected, Loopback101

      192.168.102.0/24 is variably subnetted, 2 subnets, 2 masks

C        192.168.102.0/24 is directly connected, Loopback102

L        192.168.102.1/32 is directly connected, Loopback102

      192.168.103.0/24 is variably subnetted, 2 subnets, 2 masks

C        192.168.103.0/24 is directly connected, Loopback103

L        192.168.103.1/32 is directly connected, Loopback103

R3#ping 172.30.30.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.30.30.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 16/40/68 ms