01 · FoundationsLab 4 / 59
Challengenetworking
Linux Networking & Troubleshooting — Challenge
Work a connection failure from the outside in: DNS, route, port, firewall, application — and know which layer you are on.
- Time
- 25 min
- Level
- Beginner
- Objectives
- 4 objectives
- Cost
- Free
Where this fits in the platform
Already built
This lab adds
- A method for following a connection to the layer that broke it
Which lets you
Before you start
You will need
- Linux with `dig`, `ss`, `curl`, `ip`
- sudo access
You do not need these already — the lab environment below provides them.
You will be able to
- Resolve a name and read the TTL that explains a stale answer
- Read a routing table and say where a packet would go
- Prove whether a port is open, listening, or filtered
- Work a failure in layers instead of guessing
Cost — Free
— no cloud resources
The goal#
Achieve the same outcome as Linux Networking & Troubleshooting, from an empty starting point, without the steps.
An application cannot reach its database. The developer says "the network is down". It almost never is.
This lab builds the sequence that finds the real cause in under two minutes, instead of restarting things until something changes.
Hands-on environment
Run this lab in a real terminal, free and in your browser. The environment is temporary and yours alone — break it as much as you like.
Start the challengeOpens in Killercoda, in a new tab — keep this page open for the steps.
This is the guided lab's environment — the same machine, with its walkthrough on the left. Work from the task above and leave those steps alone until you are done, or you are reading the answers.
Run it on your own machine
Run this lab on your own machine. One command starts the environment, with everything the lab needs already installed:
You will need:
- bash
- curl
git clone https://github.com/EgyKode/EgyKode-lab.git
cd EgyKode-lab
./egykode start
./egykode shellYou need Docker and Git installed. Everything else runs inside the environment. The first start downloads it and takes a few minutes; later starts are seconds.
Not sure what you already have? Run: npm run doctor — it checks and changes nothing.
Anything you tick here is your own record. EgyKode cannot see inside that terminal, so the success criteria stay self-assessed even when the environment checks your work for you.
What must be true when you are done
Step 1 of 3
What must be true when you are done#
- You can state the IP a hostname resolves to and the remaining TTL on that answer.
- You can name the interface and gateway a packet to 1.1.1.1 would leave by.
- You can distinguish 'connection refused' from 'timed out' and say what each implies.
- Given a failing connection, you can name which layer is at fault before changing anything.
Rules#
- Do not open the guided lab until you are finished, or until you have been stuck on the same thing for 20 minutes. Being stuck is the exercise; staying stuck is not.
- Official documentation is allowed and encouraged. In the job it is the first thing you open.
- Verify every criterion yourself with a command whose output you can read. "It looks right" is not a check.
If you get stuck#
Work in layers rather than restarting things:
- What did you expect to happen, exactly?
- What happened instead — the error text, not a paraphrase?
- Which layer is that error from?
- What is the smallest command that proves the layer below is fine?
That sequence is the skill this tier exists to build. The commands are lookup-able; the sequence is not.
You are done when
0 of 4
The concept behind it
Next up
Lab 4 of 59 on the project path