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

Archive lab

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

• If OSPF neighbors remain down: Check that both ends of each transit link share the same area (0 between CORE and ABR; 10 between ABR and BRANCH).; Ensure the correct wildcard masks for each 'network' statement. A common slip is using an overly broad wildcard that misses the exact /30.; Confirm that only the transit ports are 'no passive'; leaving a transit passive prevents hellos and the adjacency.
• If multiple specifics still appear on RTR-CORE after you configured the summary: Verify the ABR's 'area 10 range' summary statement is present and that its prefix and mask exactly cover all four component /24s.; Ensure that the component routes (10.10.0.0/24–10.10.3.0/24) are actually present in the ABR’s area 10 LSDB.
• If pings from HOST-A to HOST-B fail while OSPF looks healthy: Verify the host /30 IPs and default gateways are correct.; Check that both host point-to-point networks are in OSPF (even if passive) so return traffic is routed correctly.