Friday, October 26, 2018

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