CCNA: OSPF Passive Interfaces & Default Origination

Bundle lab

Deploy OSPFv2 across a 3-router, 2-LAN branch/core/edge topology. Mark LAN-facing interfaces as passive so they do not send OSPF hellos or form adjacencies. Originate a default route only from the edge router and verify default propagation end-to-end using real client traffic. Includes realistic troubleshooting around missing adjacencies, non-propagating defaults, and unreachable external destinations.

Learning objectives

• Configure OSPFv2 on a 3-router branch-core-edge topology using assigned addresses
• Mark stub/LAN interfaces as passive to suppress OSPF hellos and adjacencies
• Originate a default route from the edge router into OSPF
• Verify OSPF neighbor adjacencies and learned default routes with end-to-end tests
• Troubleshoot non-forming adjacencies and missing default routes

Troubleshooting focus

• No OSPF neighbor forms on a transit: check show ip ospf neighbor on both ends. Confirm both sit in 10.0.12.0/30 (or 10.0.23.0/30) and area 0, that MTU and hello/dead timers match, and that the transit interface is not passive.
• Verify the EDGE1-to-CORE1 adjacency is up and that EDGE advertises only the transit and Loopback0, not 203.0.113.1.
• CLIENT-USER or SRV-APP cannot ping 203.0.113.1: confirm each host reaches its gateway, that OSPF has converged and 0.0.0.0/0 is present on RTR-BR1 and RTR-CORE1, and that Loopback1 is up on RTR-EDGE1 but not advertised into OSPF.
• tcpdump -i eth0 -n 'ip proto 89' on a host still shows OSPF hellos: the LAN is not passive. show ip ospf interface brief should list the LANs as passive.