Lab Objective
Configure OSPF on a serial link between two routers, verify the network type is automatically recognized as point-to-point, confirm the neighbor relationship forms without requiring DR/BDR election, and verify route exchange.
Lab Purpose
OSPF behaves differently depending on the underlying network type, discussed earlier in this series regarding OSPF fundamentals. Point-to-point links are the simplest case, forming adjacencies quickly since there is no need to elect a Designated Router when only two devices can ever be present on the segment.
Lab Topology
R1 ---- Serial0/0/0 ------ Serial0/0/0 ---- R2
R1: 10.5.5.1/30, LAN 192.168.5.0/24
R2: 10.5.5.2/30, LAN 192.168.6.0/24Task 1: Configure Basic Addressing
Configure the serial interfaces and each router's LAN.
Task 2: Enable OSPF on Both Routers
Enable OSPF process 1 on both routers, advertising all relevant networks into area 0.
Task 3: Verify the Network Type
Confirm the serial interface is automatically recognized as a point-to-point OSPF network type.
Task 4: Verify the Neighbor Relationship
Confirm the neighbor reaches FULL state, and note the absence of any DR/BDR role.
Task 5: Verify Route Exchange
Confirm each router learns the other's LAN via OSPF.
Solution and Verification
R1(config)# interface serial0/0/0
R1(config-if)# ip address 10.5.5.1 255.255.255.252
R1(config-if)# no shutdown
R1(config-if)# exit
R1(config)# interface gigabitethernet0/0
R1(config-if)# ip address 192.168.5.1 255.255.255.0
R1(config-if)# no shutdownR2(config)# interface serial0/0/0
R2(config-if)# ip address 10.5.5.2 255.255.255.252
R2(config-if)# clock rate 64000
R2(config-if)# no shutdown
R2(config-if)# exit
R2(config)# interface gigabitethernet0/0
R2(config-if)# ip address 192.168.6.1 255.255.255.0
R2(config-if)# no shutdownR1(config)# router ospf 1
R1(config-router)# network 10.5.5.0 0.0.0.3 area 0
R1(config-router)# network 192.168.5.0 0.0.0.255 area 0R2(config)# router ospf 1
R2(config-router)# network 10.5.5.0 0.0.0.3 area 0
R2(config-router)# network 192.168.6.0 0.0.0.255 area 0R1# show ip ospf interface serial0/0/0
Serial0/0/0 is up, line protocol is up
Internet Address 10.5.5.1/30, Area 0
Network Type POINT_TO_POINT, Cost: 64
-- Automatically detected as point-to-point,
-- since serial interfaces default to this
-- OSPF network typeR1# show ip ospf neighbor
Neighbor ID Pri State Dead Time Address Interface
10.5.5.2 0 FULL/ - 00:00:38 10.5.5.2 Serial0/0/0
-- Note the "-" in place of a DR/BDR role,
-- and priority 0 -- point-to-point networks
-- never elect a DR or BDR at all, since
-- with only two possible neighbors that
-- election serves no purposeR1# show ip route ospf
O 192.168.6.0/24 [110/65] via 10.5.5.2, Serial0/0/0Key Takeaway
Point-to-point OSPF network types skip DR/BDR election entirely, showing a dash instead of a role in the neighbor table — this is expected, normal behavior rather than a misconfiguration, and it also means adjacency typically forms faster than on broadcast-type networks like Ethernet, which must complete DR/BDR election before reaching FULL state.