CCNA Foundations: OSPF Day 6 — Route Summarization at the ABR

Published 2026-07-10

A compact, enterprise-clean, 5-node CML lab that builds on OSPF multi-area design. You will enable OSPF across a small core–ABR–branch topology, advertise multiple branch networks in area 10, and summarize them at the ABR using 'area range'. You will verify that specific inter-area routes are replaced by a single summary in area 0 while preserving end-to-end reachability between hosts.

Learning objectives

• Enable OSPFv2 with clean process hygiene (explicit router-id, passive-interface default, transit exceptions).
• Place interfaces into the correct OSPF areas (area 0 and a non-backbone area).
• Advertise multiple area 10 internal networks and verify inter-area LSAs on the backbone.
• Summarize area 10 at the ABR with 'area <id> range <prefix> <mask>' and confirm the backbone sees only the single summary.
• Verify end-to-end connectivity from hosts and interpret routing tables before and after summarization.

Troubleshooting focus

• Verify every link's interface status and IP addressing (`show ip interface brief`) and correct any interface that is down or misaddressed.
• Confirm each device's running configuration matches the lab objective, and bring any interface, route, or service that is not in its expected state back to health.
• Trace end-to-end reachability with ping/traceroute and isolate the first hop where forwarding fails.