Lab Objective
Configure OSPF using the point-to-multipoint network type on a hub-and-spoke topology, verify neighbors are discovered automatically without manual neighbor statements, and confirm no DR/BDR election occurs.
Lab Purpose
The non-broadcast network type covered in the previous lab requires manually configuring every neighbor relationship and still elects a DR/BDR. Point-to-multipoint offers an alternative specifically suited to hub-and-spoke topologies: it treats the network as a collection of point-to-point links, restoring automatic neighbor discovery while still supporting multiple spokes on a shared subnet.
Lab Topology
Hub-and-spoke topology (same physical layout
as the non-broadcast lab):
R1 (hub): 172.21.100.1/24
R2 (spoke): 172.21.100.2/24
R3 (spoke): 172.21.100.3/24
R2 and R3 still have no direct connectivity
to each other, only to R1Task 1: Configure Basic Addressing
Configure all three routers with their addresses on the shared subnet.
Task 2: Enable OSPF and Set the Network Type
Enable OSPF on all three routers, setting the interface network type to point-to-multipoint rather than non-broadcast.
Task 3: Verify Automatic Neighbor Discovery
Confirm neighbors form automatically without any neighbor command being configured.
Task 4: Verify No DR/BDR Election Occurs
Confirm the neighbor table shows no DR or BDR role, unlike the non-broadcast configuration in the previous lab.
Solution and Verification
R1(config)# interface serial0/0/0
R1(config-if)# ip address 172.21.100.1 255.255.255.0
R1(config-if)# ip ospf network point-to-multipoint
R1(config-if)# no shutdownR2(config)# interface serial0/0/0
R2(config-if)# ip address 172.21.100.2 255.255.255.0
R2(config-if)# ip ospf network point-to-multipoint
R2(config-if)# no shutdownR3(config)# interface serial0/0/0
R3(config-if)# ip address 172.21.100.3 255.255.255.0
R3(config-if)# ip ospf network point-to-multipoint
R3(config-if)# no shutdownR1(config)# router ospf 1
R1(config-router)# network 172.21.100.0 0.0.0.255 area 0
R2(config)# router ospf 1
R2(config-router)# network 172.21.100.0 0.0.0.255 area 0
R3(config)# router ospf 1
R3(config-router)# network 172.21.100.0 0.0.0.255 area 0
-- No neighbor commands configured anywhere,
-- unlike the non-broadcast labR1# show ip ospf neighbor
Neighbor ID Pri State Address
172.21.100.2 1 FULL/ - 172.21.100.2
172.21.100.3 1 FULL/ - 172.21.100.3
-- Neighbors formed automatically with no
-- manual neighbor statements required, and
-- the "-" in place of DR/BDR confirms no
-- election occurred at all -- point-to-multipoint
-- treats this shared subnet as a set of
-- individual point-to-point relationshipsKey Takeaway
Point-to-multipoint combines the best of both previous network types: it restores automatic neighbor discovery, avoiding the manual neighbor statements non-broadcast requires, while also skipping DR/BDR election entirely, treating each spoke relationship as its own independent point-to-point adjacency — making it frequently the preferred choice for hub-and-spoke topologies over plain non-broadcast configuration.