CCNA Static Routing: 3-Router Full-Mesh

Bundle lab

Design and implement a 3-router full-mesh with two edge LANs using static IPv4 routes only. Edges use primary defaults toward the core plus floating (higher AD) backup defaults; the core uses specific routes for the edge LANs. Validate bidirectional reachability, path choice, and failover behaviors from real hosts.

Learning objectives

• Deploy static IPv4 and default routes across a three-router full-mesh so both edge LANs reach each other.
• Use /30 point-to-point transit links and /24 routed LANs at the edges.
• Ensure correct forward and return paths using specific routes on the core and defaults (with floating-backup) on the edges.
• Verify administrative distance selection, RIB/FIB choices, and bidirectional end-to-end host reachability.
• Demonstrate failover by observing path changes and backup default activation when a link is failed.

Troubleshooting focus

• ping 10.10.3.10 from CLIENT-A fails: check the router interface on that host's LAN is up/up with the exact gateway IP, then verify each /30 transit pair shares one subnet.
• A route is in the table but nothing forwards: a static route must point at the neighbor's IP. A route to self will not forward.
• The backup path takes over too early, or not at all: the floating routes use administrative distance 5. Too low and it installs alongside the primary, causing asymmetry; omitted, it never activates on failure.
• Neighbors never ARP across a transit link: one wrong /30 mask breaks the shared subnet, and a /24 typo can overlap addressing and confuse routing.
• One direction pings but the reverse fails: look for a missing specific route on RTR-B-CORE, or a default pointed at the wrong neighbor.
• Nothing works from either host: confirm CLIENT-A uses 10.10.1.1 and CLIENT-C uses 10.10.3.1. A host default on the wrong subnet breaks everything.