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IntermediatePublished 2026-08-28

CCNA Break/Fix: Translation Happens, Replies Do Not

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Daily CCNA troubleshooting lab (repair-focused). Inside clients cannot reach an external destination even though PAT appears configured. Diagnose by reading the NAT table and interface roles, discover that translation isn’t triggering because the NAT boundary is undefined, and restore outbound reachability by correctly marking both sides.

Track
Est. time
45 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Interpret NAT/PAT behavior from show ip nat translations and show ip nat statistics
  • Differentiate inside vs. outside NAT roles and why both are required for translation
  • Validate ACL-to-NAT binding and default routing on an edge router
  • Prove end-to-end reachability from user hosts after restoring NAT

Troubleshooting focus

  • Users inside 192.168.10.0/24 cannot reach an external host (R2 loopback). R1 itself can reach it.
  • show ip nat translations on R1 is empty during client tests, suggesting no translations are being created.
  • NAT configuration (PAT overload statement and ACL) appears present; investigate interface roles and traffic direction.
  • Confirm R1 has a valid default route to the ISP and that return traffic from the ISP would be to the outside interface address.

Topology

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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.
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