The scenario
The Router's ge0 (10.0.1.1/24) connects to PC-Left (10.0.1.10). Its ge1 (10.0.1.254/24) connects to a switch with PC-Right (10.0.1.50) and Server (10.0.1.100, a web server on TCP port 80). Both router interfaces are in 10.0.1.0/24: one network number used for two separate segments. Every host has a /24 mask, so every host believes all of 10.0.1.0/24 is on its own cable. When PC-Left wants 10.0.1.50 it does not use its gateway at all; it asks with ARP on its own cable, where only the Router's ge0 is, and nobody answers. The Router is never asked to forward anything. The fix is to give the right-hand segment its own network, and to move everything on it: the Router's interface, both hosts' addresses and both hosts' gateways. OSPF is switched off on the Router; it has no neighbours to talk to anyway.
What you will work out
Understand why every router interface needs its own subnet, why overlapping subnets break at the hosts first, and what a complete renumbering involves.
Why this matters
Overlapping subnets rarely fail with a clear error. Devices on the same segment keep working, so the network looks partly healthy, while everything across the router fails before the router is even involved. When two hosts on the 'same' network cannot reach each other, compare each host's network with the cable it is actually on. And when you renumber, list everything that refers to the old addresses: interfaces, gateways, DHCP scopes, firewall rules and DNS records.
Running it
Overlapping Subnets: The Router Is Never Asked opens on a canvas, already wired and addressed. Trace a packet through it hop by hop, or run the same topology live on real Linux network namespaces. How the two modes differ.
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