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IntermediatePublished 2026-06-30

OSPF Network Types: DR/BDR, Broadcast vs P2P

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Hands-on CCNP OSPF lab comparing broadcast and point-to-point network types. Three routers share a multi-access Ethernet via an access switch to observe DR/BDR election, manipulate interface priorities, and then convert to point-to-point. Includes a user LAN behind R1 and realistic troubleshooting: neighbor stuck in 2-Way due to type mismatch, area mismatch isolating a router, and incorrect interface priority preventing desired DR/BDR roles.

Track
Est. time
85 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Deploy OSPFv2 on three routers sharing a broadcast segment and advertise loopbacks and a user LAN.
  • Observe and interpret default DR/BDR/DROTHER roles on a broadcast network.
  • Influence DR/BDR election with interface priorities and understand re-election behavior.
  • Convert an OSPF interface from broadcast to point-to-point and analyze adjacency changes and the absence of DR/BDR.
  • Diagnose and recover OSPF adjacency problems: network type mismatch (2-Way) and area mismatch (Down).
  • Verify adjacencies and end-to-end reachability from a real host on the routed LAN.

Troubleshooting focus

  • A neighbor is stuck in 2-Way and never reaches FULL: check network type consistency and multicast capability. On this Ethernet, either all routers use broadcast or all use point-to-point. Also confirm hello/dead timers and MTU match.
  • A router is isolated or a neighbor sits in Down: suspect an area mismatch on the shared segment. show ip ospf interface brief and show ip ospf neighbor identify the odd router. Correct the area and reset the adjacency if needed.
  • show ip ospf neighbor does not show R2 as DR and R1 as BDR: confirm the ip ospf priority values on Ethernet0/1. Elections do not re-run automatically after a priority change — flap the OSPF process or the interface.
  • CLIENT-A10 cannot reach 10.255.0.2 or 10.255.0.3: ensure R1 advertises 10.10.10.0/24 into OSPF and that R2/R3 have routes back to the user LAN. From the client, verify the default gateway and subnet mask; from R1, verify the OSPF routes to the remote loopbacks.

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How this lab is graded
  • Build it your way. Where a lab lets you choose a value — a VLAN name, an interface description — grading checks that you configured it, not which name you picked. Names that another line has to reference, like an ACL applied with access-class, are stated in the guide and do have to match.
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