Linux · Systems fluency
What are the Linux networking basics you need in production?
Short answer
Production troubleshooting usually starts with addresses, routes, ports, and name resolution. Know the difference between listening sockets, established connections, and packets that never reach the host.
An interface has an IP address and prefix. The kernel chooses a route for each destination, using the default gateway when no more specific route matches. TCP provides ordered, reliable streams; UDP is connectionless and leaves reliability to the application.
ip -br addr
ip route
ss -tulpnThe mental model
- Address and prefix determine whether a destination is local
- The route table selects the next hop and interface
- A listening socket waits for connections on an address and port
- DNS maps names to addresses before the client can connect
- A firewall can drop traffic without the application ever seeing it
Test in layers rather than jumping straight to ping. Check the address, route, DNS answer, TCP handshake, and application response. Ping can be blocked while the service is healthy, so its failure is not proof that the service is down.
Follow-ups you should expect
Interviewers use these to check whether the first answer was understanding or memorisation.
- 1What is the difference between TCP and UDP?
- 2Why can ping fail while HTTPS still works?
- 3What does a default gateway do?
- 4How do you check whether a port is listening?
Say it in the interview
I reason from layers: address, route, DNS, TCP connection, then application. An interface has an address and prefix, the route table selects the next hop, and a listening socket waits on a port. Ping is not a reliable health check because it can be blocked. I verify each layer with ip, ss, and DNS tools before changing anything.
Use this as a model, not a script. Saying it in your own words is what makes it survive follow-up pressure.
Related questions
Reading is step one
Now say it out loud.
Understanding an answer and delivering it under pressure are different skills. Rehearse this topic in a live Linux mock interview and get scored feedback on depth, clarity and confidence.