← lab guides · 2026-08-10 · 120m

OSPF Single-Area Lab

Three-router OSPF, loopbacks, and passive-interface hygiene.

topic: routing-switching · tool: cisco-ios, eve-ng · difficulty: intermediate

TOPOLOGYFig. — lab diagram

[ LAB TOPOLOGY — add topology.svg to this bundle ]
  [ PC1 ]──[ SW1: vlan10 ]──[ R1 ]──[ FW ]── Internet
              └─ vlan99 MGMT  vlan20 OT (PLC/HMI)

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Objective

You bring up OSPF area 0 on R1, R2, and R3. You advertise loopbacks and you test how passive-interface stops hellos.

Steps

Assign 10.0.x.y to point-to-point links and 1.1.1.x/32 to loopbacks.
On each router, run router ospf 1 and add network 10.0.0.0 0.0.0.255 area 0.
Check show ip ospf neighbor and show ip route ospf.
Set passive-interface default, then add no passive-interface on transit links. Watch how adjacency holds.

Gotcha

You must add the loopback to OSPF with a network statement. OSPF does not include it by itself. I missed 1.1.1.3/32 and thought redistribution had broken.

Takeaways

OSPF sends hellos per interface
Loopbacks give you a stable router ID
Watch DBD and LSR with Wireshark filter ospf

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