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IntermediatePublished 2026-07-09

CCNA Foundations: OSPF Day 5 — Multi-Area OSPF & the ABR

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Build and verify a compact, enterprise-clean multi-area OSPF network with an ABR. Configure area 0 and a non-backbone area, advertise loopbacks and LANs, enforce OSPF hygiene (passive LANs, explicit router-ids), and verify O IA inter-area routes from the endpoints.

Track
Est. time
55 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Configure OSPFv2 across two areas with an ABR on the boundary
  • Assign stable router-ids from loopbacks and advertise LAN and transit networks
  • Apply passive-interface default and selectively enable OSPF hellos on transit links
  • Verify OSPF adjacencies and inter-area (O IA) routes
  • Prove end-to-end host reachability across areas with ping and traceroute

Troubleshooting focus

  • A neighbor never reaches FULL, or sticks in EXSTART/EXCHANGE: confirm both ends of that transit are in the same area ID and share default timers and MTU. show ip ospf interface shows the area and timers per interface.
  • An interface or LAN never appears in OSPF: check the wildcard mask matches the exact connected subnet, e.g. 10.0.12.0 0.0.0.3 for a /30. Too broad or too narrow misses the interface.
  • Router-ids show as 0.0.0.0 or change after OSPF starts: set the router-id explicitly to the Loopback0 address, then clear ip ospf process (out of production hours) to make it take.
  • Pings from HOST-A or HOST-B fail on their own LAN: verify the host IP and default gateway match the addressing plan precisely.

Topology

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Grade your work

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.
  • Addresses, modes and protocol keywords are exact. An IP address, a subnet mask, switchport mode trunk, an encapsulation — these carry the meaning of the lab, so they are graded as written in the guide.
  • Grading reads your saved configuration. Export the lab from CML after you have configured it, and make sure anything you set is in the running-config — a change that only exists in a terminal session never reaches the grader.
  • You can submit as many times as you like. Your best score stands, and each attempt tells you which checks passed so you can work the gaps.
  • Scored something you believe is correct? Use Report an issue on this page — that is exactly how the grading fixes in the changelog got found.

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