Learning path

Computer networks

Learn protocol layering, IP addressing, TCP and UDP sockets, HTTP messages, and how routers choose where to send a packet.

About this subject

Computer networks connect machines so programs on them can exchange data. The Internet is organized in layers: links move frames between neighbours, IP moves packets across networks, TCP and UDP connect programs, and application protocols such as HTTP define what the programs say.

This path covers layering and encapsulation, IP addressing and subnets, TCP and UDP sockets on the loopback interface, HTTP request and response messages, and longest-prefix-match forwarding. Each lesson uses a small, complete program that runs on its own. Python has the full sequence. The other languages listed below add lessons that use that language's own idioms and standard library, such as Java threads, C++ smart pointers, C# LINQ, or Node.js streams, and appear only for the topics the language supports. The programs are simplified models chosen to make an idea visible, so they are a foundation for further study rather than a replacement for a full course or for production-grade software.

Before you start: Strings, bytes, dictionaries, and basic threads.

1
Python
Readable code for automation, data, and first programs.
Protocol layers and encapsulation
Wrap data in transport, network, and link headers on the way down and unwrap it on the way up.
IP addressing, CIDR, and subnets
Read a prefix length, count addresses and usable hosts, and split a network into subnets.
TCP sockets: a loopback echo server
Open a listening socket, connect a client, and exchange bytes over a reliable stream.
UDP datagrams
Send independent datagrams with no connection and see how UDP differs from TCP.
HTTP messages: requests, responses, and status codes
Read the text structure of an HTTP/1.1 request and response, and parse a response by hand.
Forwarding with longest-prefix match
Choose the next hop by finding the most specific route that matches a destination address.
2
C
Learn memory, pointers, and efficient systems programming.
C: the CRC-32 frame check sequence
Compute the cyclic redundancy check used by Ethernet and detect a single flipped bit.
C: network, broadcast, and host count of a CIDR block
Use shifts and masks on a 32-bit address to describe a subnet.
3
C++
Build fast applications with modern types and classes.
C++: the Internet checksum
Compute the 16-bit ones'-complement checksum used by IP, TCP, and UDP, and use it to detect corruption.
C++: forwarding with longest-prefix match
Pick the most specific route that matches a destination address, as a router does.
4
Java
Understand object oriented programs and the JVM.
Java: a TCP echo server on the loopback interface
Open a server socket on an ephemeral port and connect to it with a client socket in the same program.
Java: IPv4 addresses, masks, and CIDR blocks
Compute the network address, broadcast address, and host count of a subnet with bitwise operations.
5
C#
Build typed applications on .NET.
C#: a TCP echo server on the loopback interface
Use TcpListener and TcpClient with async methods to send a line and read the reply.
C#: IPv4 subnets with IPAddress and bit masks
Compute the network and broadcast addresses for a CIDR block and test whether addresses belong to it.
6
JavaScript
Add behavior to the web and build applications.
JavaScript: an HTTP server and client on the loopback interface
Start a Node.js HTTP server on a free port and request it with fetch to see status codes.
JavaScript: a TCP echo server with the net module
Send a line through a TCP socket and print the server's reply.
7
TypeScript
JavaScript with static types for dependable code.
TypeScript: parsing a raw HTTP request into a typed object
Split the request line, headers, and body of an HTTP/1.1 message and read a query parameter.
8
HTML
Structure accessible web pages.
HTML Forms: GET versus POST
See what each form method sends over HTTP and when to use it.

About this subject

Python

Protocol layers and encapsulation

IP addressing, CIDR, and subnets

TCP sockets: a loopback echo server

UDP datagrams

HTTP messages: requests, responses, and status codes

Forwarding with longest-prefix match

C

C: the CRC-32 frame check sequence

C: network, broadcast, and host count of a CIDR block

C++

C++: the Internet checksum

C++: forwarding with longest-prefix match

Java

Java: a TCP echo server on the loopback interface

Java: IPv4 addresses, masks, and CIDR blocks

C#

C#: a TCP echo server on the loopback interface

C#: IPv4 subnets with IPAddress and bit masks

JavaScript

JavaScript: an HTTP server and client on the loopback interface

JavaScript: a TCP echo server with the net module

TypeScript

TypeScript: parsing a raw HTTP request into a typed object

HTML

HTML Forms: GET versus POST