Networks · 6 min
Reading a network route
When a connection fails, follow decisions in order: name, route, transport, application.
Resolve the name
Write down every returned address. IPv4 and IPv6 can take different paths, so testing only one can hide the actual failure.
Ask the routing table
Do not guess which interface will be used. Query the route for the exact destination and note the next hop and source address. On a busy router, policy rules may matter more than the main table.
Observe the handshake
A packet capture can separate “nothing left the host” from “the peer did not answer.” Then move up one layer: transport success does not guarantee that the application accepted the request.
The useful habit is to record each boundary and its evidence. That turns a vague outage into a short list of falsifiable statements.