Netpractice 42 Tutorial May 2026

The NetPractice project at 42 is a 10-level networking exercise designed to teach the fundamentals of TCP/IP addressing, subnetting, and routing. Unlike other 42 projects, it requires no code; instead, you use an interactive training interface to configure network parameters until all nodes can communicate successfully. Core Concepts to Master

To clear all 10 levels, you must understand how these components interact:

IP Addressing (IPv4): A 32-bit address (e.g., 192.168.1.1) split into a network part and a host part.

Subnet Masks: Defines the boundary between the network and host. For example, a mask of 255.255.255.0 (or /24) means the first 24 bits are for the network.

Routing Tables: Instructions for a device on where to send data. If a destination is outside the local network, it must go through a default gateway (usually a router interface). Reserved Addresses: netpractice 42 tutorial

Network Address: The first address in a range (host bits are all 0).

Broadcast Address: The last address in a range (host bits are all 1). Loopback: 127.0.0.1, used for internal testing. Level-by-Level Breakdown

The difficulty scales from simple single-network setups to complex multi-router environments.

Given IP 10.0.0.42 and mask 255.255.255.240 (/28): The NetPractice project at 42 is a 10-level

A red flag surfaced: an anomalous burst from an unknown IP. The tutorial prompted her to quarantine the source and initiate a tracing routine. Lena enabled deep logs and watched for indicators of compromise. The system suggested remediation steps; she applied an automated block and notified the simulated SOC. The attack faded like a storm passing.

Let's walk through the logical progression.

Scenario: Private LAN → Router → Internet.

Final router towards internet needs a default route:
0.0.0.0/0 → next-hop (ISP gateway) Given IP 10

All other routers propagate reachability.

NetPractice is a web-based training tool designed to teach TCP/IP addressing and routing logic through practical exercises. The interface consists of a network diagram (boxes for computers, switches, routers) and configuration panels.

Why 42 loves it:

The goal: Complete 10 levels (from basic to incredibly complex) with 100% success.

On the screen, you will see several key elements:

  • Switch: A grey box connecting cables. Switches connect devices on the same network. They do not have IP addresses.
  • Router: A yellow box. Routers connect different networks. A router usually has multiple interfaces (e.g., eth0, eth1), each belonging to a different network.
  • Routing Table: A list of rules that tells a device: "If you want to talk to Network X, send the packet through Interface Y."

    • Router A left: 10.0.0.1/24
    Router A right: 192.168.1.1/30 connected to Router B left: 192.168.1.2/30
    Router B right: 172.16.1.1/24 (LAN: PC at 172.16.1.10)
    Question: What route needs to be on Router A to reach the PC?
    Answer: Destination: 172.16.1.0/24 via Gateway: 192.168.1.2