Linux Labs
Where to start First steps track · 15 stages
Linux Labs
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Networking

From addresses and routes to ports, filtering, DNS, SSH and multi-host connectivity.

14 stages9 labs~9 hours medium medium

Progress Stages: 0 of 14

The track has not been started. The first stage is «Interfaces, addresses and subnets», ~30 min.

Start stage 1

Module 1

Addresses and routes

Interfaces, addresses and prefixes, route and gateway selection, persistent network configuration with Netplan.

4 stages · ~3 hours

  1. Stage 1 of 14

    1 · Interfaces, addresses and subnetsInterfaces, addresses and subnets

    8 steps · ~30 min 8 steps · ~30 min
    1. The server does not answer exercises 0 of 1 on a machine 4 min
    2. 2 An interface and its addresses on a machine 5 min
    3. 3 A practice network inside the machine theory 4 min
    4. 4 What /24 means theory 5 min
    5. 5 Give the client its neighbour back on a machine 3 min
    6. 6 What a ping reply proves theory 4 min
    7. 7 A different prefix, different neighbours on a machine 3 min
    8. 8 Summary summary 2 min
    Start stage 1
  2. Stage 2 of 14

    2 · How Linux picks a routeHow Linux picks a route

    7 steps · ~30 min 7 steps · ~30 min
    1. The neighbour answers, the service does not exercises 0 of 1 on a machine 5 min
    2. 2 The routing table theory 6 min
    3. 3 A route to a single address on a machine 4 min
    4. 4 Ask the kernel about the path theory 4 min
    5. 5 The most specific route theory 5 min
    6. 6 A network behind the neighbour on a machine 4 min
    7. 7 Summary summary 2 min
    Start stage 2
  3. Stage 3 of 14

    3 · Persistent networking with NetplanPersistent networking with Netplan

    9 steps · 2 labs · ~1 hour 9 steps · 2 labs · ~1 hour
    1. The fix is gone exercises 0 of 1 on a machine 5 min
    2. 2 Where the network configuration lives theory 5 min
    3. 3 Check, then apply on a machine 6 min
    4. 4 Every file in the directory is one configuration theory 4 min
    5. 5 Three checks of the result theory 4 min
    6. 6 An old copy in the directory on a machine 4 min
    7. 7 Netplan: restore the link to the neighbour easy lab 25 min
    8. 8 A service behind the neighbour medium lab 30 min
    9. 9 Summary summary 2 min
    Start stage 3
  4. 4 · Module test 10 questions · pass mark 70%

Module 2

Ports and firewall

Which process listens on a port, how to test a service from the right side and open access in nftables for a single source.

4 stages · ~2 hours

  1. Stage 5 of 14

    5 · Who is listening on a portWho is listening on a port

    9 steps · 1 lab · ~50 min 9 steps · 1 lab · ~50 min
    1. The site answers only itself exercises 0 of 1 on a machine 4 min
    2. 2 Ports and sockets theory 4 min
    3. 3 Who is listening: ss on a machine 4 min
    4. 4 Which address a socket waits on on a machine 5 min
    5. 5 A site for the neighbour on a machine 4 min
    6. 6 The port is already in use theory 4 min
    7. 7 A page for insiders only on a machine 3 min
    8. 8 Ports: start the app service medium lab 20 min
    9. 9 Summary summary 2 min
    Start stage 5
  2. Stage 6 of 14

    6 · From connection to application responseFrom connection to application response

    7 steps · ~30 min 7 steps · ~30 min
    1. Three “the site is down” complaints exercises 0 of 1 on a machine 5 min
    2. 2 Refusal and timeout theory 5 min
    3. 3 The answer's status and curl's code on a machine 5 min
    4. 4 What an answer means theory 5 min
    5. 5 A report someone can repeat theory 4 min
    6. 6 A check for monitoring on a machine 4 min
    7. 7 Summary summary 2 min
    Start stage 6
  3. Stage 7 of 14

    7 · Allow what is needed, keep the blockAllow what is needed, keep the block

    8 steps · 1 lab · ~55 min 8 steps · 1 lab · ~55 min
    1. A listener, yet the client waits exercises 0 of 1 on a machine 5 min
    2. 2 Table, chain, rule on a machine 4 min
    3. 3 Rules in order on a machine 6 min
    4. 4 Fix the file and load it on a machine 5 min
    5. 5 A check from both sides theory 4 min
    6. 6 A rule out of place on a machine 4 min
    7. 7 Firewall: open the site to the office medium lab 25 min
    8. 8 Summary summary 2 min
    Start stage 7
  4. 8 · Module test 10 questions · pass mark 70%

Module 3

DNS and SSH

Where the system looks up an address for a name and how to fix the DNS server; what SSH checks at login, key file modes and the sshd settings in force.

3 stages · ~2 hours

  1. Stage 9 of 14

    9 · Why the address works and the name does notWhy the address works and the name does not

    8 steps · 1 lab · ~45 min 8 steps · 1 lab · ~45 min
    1. The site answers by address, not by name exercises 0 of 1 on a machine 5 min
    2. 2 Who looks up the address for a name on a machine 5 min
    3. 3 Ask the DNS server directly on a machine 6 min
    4. 4 "No such name" and "the server is silent" on a machine 4 min
    5. 5 resolv.conf on a stock Ubuntu theory 4 min
    6. 6 Fix the setting where it is taken from on a machine 4 min
    7. 7 Internal names do not resolve easy lab 15 min
    8. 8 Summary summary 2 min
    Start stage 9
  2. Stage 10 of 14

    10 · SSH — trusting the server and logging in with a keySSH — trusting the server and logging in with a key

    9 steps · 2 labs · ~1 hour 9 steps · 2 labs · ~1 hour
    1. The key is in place, yet the login fails exercises 0 of 1 on a machine 5 min
    2. 2 Two checks at login theory 4 min
    3. 3 Why the server distrusts the file on a machine 4 min
    4. 4 The server key changed on a machine 5 min
    5. 5 What the server actually allows on a machine 6 min
    6. 6 Give key login back on a machine 4 min
    7. 7 SSH key login isn't working medium lab 20 min
    8. 8 Keep only the authorized SSH access medium lab 25 min
    9. 9 Summary summary 2 min
    Start stage 10
  3. 11 · Module test 10 questions · pass mark 70%

Module 4

Networking between hosts

Two machines: tell from the failure where the break is — route, return path, filter or listener — and get the site answering the neighbour.

3 stages · ~2 hours

  1. Stage 12 of 14

    12 · Diagnosing between two machinesDiagnosing between two machines

    7 steps · 1 lab · ~55 min 7 steps · 1 lab · ~55 min
    1. The site answers at home, not to the neighbour exercises 0 of 1 on a machine 5 min
    2. 2 Whose observation is it theory 5 min
    3. 3 A specific route overrides the network on a machine 6 min
    4. 4 Two real machines theory 4 min
    5. 5 Find the faulty side on a machine 3 min
    6. 6 Connect two VMs over the network medium lab 30 min
    7. 7 Summary summary 2 min
    Start stage 12
  2. Stage 13 of 14

    13 · Restore a service from client to answerRestore a service from client to answer

    7 steps · 1 lab · ~1 hour 7 steps · 1 lab · ~1 hour
    1. The filter is gone, yet the site is silent exercises 0 of 1 on a machine 6 min
    2. 2 The kind of failure points to the stage theory 6 min
    3. 3 A listener on the right address on a machine 8 min
    4. 4 When the restore is complete theory 4 min
    5. 5 The last fault — on two machines on a machine 4 min
    6. 6 Site unreachable from another host hard lab 40 min
    7. 7 Summary summary 2 min
    Start stage 13
  3. 14 · Module test 10 questions · pass mark 70%

  1. Final lab

    Site unreachable from another host ~40 min
  2. Final test 18 questions · pass mark 80%

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