This post is a continuation of my previous post on OSPF Network Types.

OBJECTIVE:

   1.  To understand how OSPF Broadcast Network Type works.
   2.  To determine the proper way of configuring OSPF Broadcast network.
   3.  Determine how the DR & BDR are elected on a OSPF Broadcast network.

I have created the same GNS3 Topology to emulate the characteristics of an OSPF BROADCAST Network.

 

Below is the MANILA Router Configurations:

 R1#config t
Enter configuration commands, one per line.  End with CNTL/Z.
R1(config)#hostname MANILA
MANILA(config)#int s2/0
MANILA(config-if)#ip add 192.168.12.1 255.255.255.0
MANILA(config-if)#no shut
MANILA(config-if)#encapsulation frame-relay
MANILA(config-if)#ip ospf network broadcast
MANILA(config-if)#

MANILA(config)#router ospf 1
MANILA(config-router)#network 192.168.12.0 0.0.0.255 area 0
MANILA(config-router)#^Z

Below is the MELBOURNE Router Configurations:

R2#config t
Enter configuration commands, one per line.  End with CNTL/Z.
R2(config)#hostname MELBOURNE
MELBOURNE(config)#int s2/0
MELBOURNE(config-if)#ip add 192.168.12.2 255.255.255.0
MELBOURNE(config-if)#no shut
MELBOURNE(config-if)#encapsulation frame-relay
MELBOURNE(config-if)#ip ospf network broadcast
MELBOURNE(config-if)#exit

MELBOURNE(config)#router ospf 1
MELBOURNE(config-router)#network 192.168.12.0 0.0.0.255 area 0
MELBOURNE(config-router)#^Z
MELBOURNE#

Below is the SINGAPORE Router Configurations:

R3#config t
Enter configuration commands, one per line.  End with CNTL/Z.
R3(config)#hostname SINGAPORE
SINGAPORE(config)#int s2/0
SINGAPORE(config-if)#ip add 192.168.12.3 255.255.255.0
SINGAPORE(config-if)#no shut
SINGAPORE(config-if)#encapsulation frame-relay
SINGAPORE(config-if)#ip ospf network broadcast
SINGAPORE(config-if)#exit

SINGAPORE(config)#router ospf 1
SINGAPORE(config-router)#network 192.168.12.0 0.0.0.255 area 0
 
Now, let’s verify my configurations:

MANILA#show frame-relay map
Serial2/0 (up): ip 192.168.12.2 dlci 101(0x65,0x1850), dynamic,
              broadcast,, status defined, active
Serial2/0 (up): ip 192.168.12.3 dlci 102(0x66,0x1860), dynamic,
              broadcast,, status defined, active

>>> As Observed above, the results of the frame relay map shows the entries learned through Inverse ARP, the statically configured maps (as per the frame relay switch set up) and the connections established from MANILA to both MELBOURNE & SINGAPORE routers.

Now, let’s check the OSPF Neighbor status between the three routers:

MANILA#sh ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
192.168.12.2      1   FULL/DROTHER    00:00:38    192.168.12.2    Serial2/0
192.168.12.3      1   FULL/BDR        00:00:39    192.168.12.3    Serial2/0
MANILA#

>>After the final HELLO PACKETS(FULL), we can see that OSPF adjacency were established and as seen from MANILA router, SINGAPORE router were elected as the BDR.
 
MELBOURNE#show ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
192.168.12.1      1   FULL/DR         00:00:36    192.168.12.1    Serial2/0
MELBOURNE#

 >>> As observed from the MELBOURNE router ospf adjacency, MANILA were elected as the DR.

SINGAPORE#sh ip ospf neighbor

Neighbor ID     Pri   State           Dead Time   Address         Interface
192.168.12.1      1   FULL/DR         00:00:32    192.168.12.1    Serial2/0
SINGAPORE#

 >>> Similarly, SINGAPORE router shows that MANILA were the DR.

Now, I will advertise the loopback address on each of three routers and check the reachability from one another. Here are the configurations of the three routers :

MANILA#config t
Enter configuration commands, one per line.  End with CNTL/Z.
MANILA(config)#int lo0
MANILA(config-if)#ip address 10.10.10.1 255.255.255.0
MANILA(config-if)#exit

MANILA(config)#router ospf 1
MANILA(config-router)#network 10.10.10.0 0.0.0.255 area 0
MANILA(config-router)#

MELBOURNE#config t
Enter configuration commands, one per line.  End with CNTL/Z.
MELBOURNE(config)#int lo0
MELBOURNE(config-if)#ip add 20.20.20.1 255.255.255.0
MELBOURNE(config-if)#exit

MELBOURNE(config)#router ospf 1
MELBOURNE(config-router)#network 20.20.20.0 0.0.0.255 area 0
MELBOURNE(config-router)#^Z
SINGAPORE#config t
Enter configuration commands, one per line.  End with CNTL/Z.
SINGAPORE(config)#int lo0
SINGAPORE(config-if)#ip add 30.30.30.1 255.255.255.0
SINGAPORE(config-if)#exit

SINGAPORE(config)#router ospf 1
SINGAPORE(config-router)#network 30.30.30.0 0.0.0.255 area 0
SINGAPORE(config-router)#^Z

Now, let’s check the results of the ROUTING TABLE of the three routers:


MANILA#show 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, H – NHRP, l – LISP
       + – replicated route, % – next hop override

Gateway of last resort is not set

      20.0.0.0/32 is subnetted, 1 subnets
O        20.20.20.1 [110/65] via 192.168.12.2, 00:03:55, Serial2/0
      30.0.0.0/32 is subnetted, 1 subnets
O        30.30.30.1 [110/65] via 192.168.12.3, 00:02:57, Serial2/0
MANILA#

>>> We can see that the loopback address of both MELBOURNE & SINGAPORE routers were received and included in MANILA router’s routing table.

MELBOURNE#show 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, H – NHRP, l – LISP
       + – replicated route, % – next hop override

Gateway of last resort is not set

      10.0.0.0/32 is subnetted, 1 subnets
O        10.10.10.1 [110/65] via 192.168.12.1, 00:05:32, Serial2/0
      30.0.0.0/32 is subnetted, 1 subnets
O        30.30.30.1 [110/65] via 192.168.12.3, 00:05:02, Serial2/0
MELBOURNE#

SINGAPORE#sho 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, H – NHRP, l – LISP
       + – replicated route, % – next hop override

Gateway of last resort is not set

      10.0.0.0/32 is subnetted, 1 subnets
O        10.10.10.1 [110/65] via 192.168.12.1, 00:05:57, Serial2/0
      20.0.0.0/32 is subnetted, 1 subnets
O        20.20.20.1 [110/65] via 192.168.12.2, 00:06:28, Serial2/0
SINGAPORE#

>>> Similarly, both MELBOURNE and SINGAPORE routers have the correct routing table entries.

VERIFICATIONS:

MELBOURNE#ping 10.10.10.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.10.10.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 52/55/60 ms
 
MELBOURNE#ping 30.30.30.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 30.30.30.1, timeout is 2 seconds:
…..
Success rate is 0 percent (0/5)
MELBOURNE#

 As observed above, I can reach MANILA router’s loopback interface but not SINGAPORE router’s Loopback. As mentioned before, we have to enable frame relay mapping on the routers to enable connectivity. MANILA Router should have no issue reaching the Loopback interface of both MELBOURNE & SINGAPORE but we need to set up the static map “frame relay map” on the MELBOURNE & SINGAPORE router.

 MANILA#ping 20.20.20.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 20.20.20.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 56/57/60 ms

MANILA#ping 30.30.30.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 30.30.30.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 40/48/60 ms
MANILA#

 So here is the configurations for both MELBOURNE & SINGAPORE.

 MELBOURNE#config t
Enter configuration commands, one per line.  End with CNTL/Z.
MELBOURNE(config)#int s2/0
MELBOURNE(config-if)#frame-relay map ip 192.168.12.3 202
MELBOURNE(config-if)#^Z

MELBOURNE#ping 30.30.30.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 30.30.30.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 56/75/84 ms
MELBOURNE#

 SINGAPORE#config t
Enter configuration commands, one per line.  End with CNTL/Z.
SINGAPORE(config)#int s2/0
SINGAPORE(config-if)#frame-relay map ip 192.168.12.2 203
SINGAPORE(config-if)#^Z

SINGAPORE#ping 20.20.20.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 20.20.20.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 60/75/88 ms
SINGAPORE#

 >> As observed, we can already reach the loopback interface of both the MELBOURNE & SINGAPORE routers.