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BeginnerPublished 2026-06-30

Default Routes & the Gateway of Last Resort

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Build a small hub-and-branch network to master default static routes and the gateway of last resort. Each branch uses a default route toward the hub; the hub holds specific routes back to branch LANs. Verify routing tables and end-to-end host connectivity, then troubleshoot common misconfigurations.

Track
Est. time
55 minutes
Difficulty
Beginner
Topics

Learning objectives

  • Configure a default static route (gateway of last resort) on branch routers.
  • Configure specific static routes to branch LANs on the hub router.
  • Verify route installation with show commands and interpret the gateway of last resort.
  • Validate host-to-host connectivity across the hub-and-branch topology.
  • Troubleshoot missing default routes, wrong next-hops, and interface/address issues.

Troubleshooting focus

  • Pings work one way only: confirm RTR-HQ has the /24 static routes to 192.168.10.0/24 via 10.0.0.2 and 192.168.20.0/24 via 10.0.0.6.
  • A route looks right but traffic still dies: ensure every used interface shows up/up and that both ends of each /30 share the same subnet and mask.
  • HOST-BR1 must default via 192.168.10.1 and HOST-BR2 via 192.168.20.1.

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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