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Networking basics flashcards

How data really travels: IP addresses, ports, TCP and UDP, routers, NAT, subnets, Wi-Fi and the commands to debug any connection.

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Beginner friendly, starts from zero
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Networking basicsStart from zero · 1 of 11

What is a computer ?

Two or more devices connected so they can send data to each other, by cable or by radio like Wi-Fi. Your home Wi-Fi with a phone, laptop and TV is a small .

Connected devices that can talk.
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What you will learn

  1. Start from zero

    • What a network is3 cards
    • Key words6 cards
    • Everyday problems2 cards

  2. Core basics

    • IP addresses3 cards
    • Home network parts4 cards
    • Ports and protocols4 cards
    • First commands and speed6 cards

  3. Next steps

    • Subnets and CIDR3 cards
    • Layers and TCP in practice5 cards
    • HTTPS, TLS and IPv64 cards
    • Firewalls, VPNs and Wi-Fi4 cards
    • The page load journey2 cards

  4. Go deeper

    • Packets and TCP performance4 cards
    • Modern protocols and routing4 cards
    • Load balancing and packet capture4 cards
    • Cloud networks2 cards
    • Security and debugging3 cards

Final test and certificate

10 questions drawn fresh from the whole topic, about 15 minutes. Sign in, score 80% or more and get a free certificate with your name and a public check link anyone can open, such as an employer or a teacher. Not signed in? Try a practice test from the cards.

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About these cards

  • Reviewed 26 October 2026
  • CoversIPv4 and IPv6TCP (RFC 9293)HTTP/3 over QUICLinux iproute2 tools
How these cards are made

Networking basics at a glance

Networking is how computers find each other and pass messages, from your phone to a website on the other side of the world.

The internet works like the postal system. Every device has an address, messages are split into numbered envelopes, and post offices (routers) pass each envelope one step closer to its destination.

Words you will meet

Network
Two or more devices connected so they can send data to each other
IP address
The number that tells the network where a device is, like a house address
Packet
A small envelope of data; big messages are split into many packets
Router
A box that passes packets between networks toward their destination
Port
A numbered door on a device that leads to one program, like 443 for secure websites
Protocol
Agreed rules for how two devices talk, like TCP or HTTP
DNS
The internet's phone book that turns names like example.com into IP addresses
Bandwidth and latency
How much data fits per second, and how long one trip takes

The steps

  1. 1. Start from zero (11 cards): What a network is, how the internet is like the postal system, and the eight words every later card uses.
  2. 2. Core basics (17 cards): IP addresses, private and public, routers and gateways, DHCP, NAT, ports, TCP and UDP, and your first debugging commands.
  3. 3. Next steps (18 cards): Subnets and CIDR, layers, the TCP handshake, TLS and HTTPS, IPv6, firewalls, VPNs, Wi-Fi and the full page-load journey.
  4. 4. Go deeper (17 cards): MTU and fragmentation, congestion control, QUIC and HTTP/3, BGP and anycast, load balancers, packet capture and cloud network design.
All 11 cards in Start from zero
What is a computer network?
Two or more devices connected so they can send data to each other, by cable or by radio like Wi-Fi. Your home Wi-Fi with a phone, laptop and TV is a small network.
What is the internet, then?
The internet is a network of networks: millions of home, office, mobile and company networks joined together, all following the same rules so any device can reach any other.
How is sending data like posting letters?
Your message is split into small envelopes (packets), each with a from and to address. Post offices (routers) pass each one closer to the destination, and the receiver puts them back in order.
What is an IP address?
A number that says where a device is on a network, like 192.168.1.24 at home or 203.0.113.80 for a website. Packets carry it so routers know where to send them.
What does a router do?
A router joins networks and passes packets along. Your home router connects your Wi-Fi to your internet provider; bigger routers pass traffic between cities and countries.
What is a port?
A numbered door on a device that leads to one program. A web server listens on 443 for HTTPS, so the IP finds the building and the port finds the right room.
What is a protocol?
An agreed set of rules for talking, like a common language. TCP makes delivery reliable, HTTP is how browsers ask for pages, and Wi-Fi is how devices talk over radio.
What is DNS, in one line?
DNS is the phone book of the internet: you type example.com and DNS looks up the IP address, because computers connect using numbers, not names.
Bandwidth and latency: what is the difference?
Bandwidth is how much data can flow per second, like the width of a road. Latency is how long one trip takes, like the drive time. A video call needs low latency more than huge bandwidth.
Wi-Fi says "connected, no internet". What does that mean?
Your device reached the home router fine, but the router cannot reach the internet provider, or names are not being looked up. Restarting the router or checking the provider is the first step.
What do you need before starting, and what can you do after?
Nothing but curiosity and a computer. After this topic you can explain how a web page reaches you, read addresses and ports, and track down why something cannot connect.
Networking basics cheatsheet

Look around

  • ip addr Your addresses per network card
  • ip route Routes and default gateway
  • ip neigh Known neighbours (ARP)
  • sudo ss -tlnp Listening TCP ports and programs
  • curl -s https://ifconfig.me Your public IP

Test a connection

  • ping -c 4 HOST Reachable? Round-trip time
  • dig NAME +short What IP a name points to
  • nc -zv HOST PORT Is the port open
  • curl -v https://HOST DNS, TCP, TLS and HTTP steps
  • mtr -rwc 50 HOST Where loss and delay start
  • sudo tcpdump -i any -n port 443 Watch packets live

Ports

  • 22 SSH
  • 53 DNS
  • 80 / 443 HTTP / HTTPS (443 UDP for HTTP/3)
  • 587 Email sending
  • 5432 / 3306 PostgreSQL / MySQL
  • 6379 Redis

Address maths

  • 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16 Private IPv4 ranges
  • /24 256 addresses
  • /16 65,536 addresses
  • /28 16 addresses
  • 127.0.0.1 / ::1 This machine
  • 0.0.0.0 Listen on every interface

Error clues

  • Connection refused Host up, nothing on that port
  • Connection timed out Dropped by firewall or wrong host
  • Name or service not known DNS lookup failed
  • Small works, big hangs MTU problem
  • Many RST packets Something is killing connections
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