🛠 Gigabit Ethernet natif et administration à distance en SSH

Objectives

Leverage the major new feature of the Pi 4B: native Gigabit Ethernet in the SoC (dedicated RGMII link to a Broadcom PHY), much faster than the 300 Mbit/s limit imposed by USB on the 3B+. Configure the network, measure the actual throughput, and administer the board via SSH without a screen.

Hardware

• Raspberry Pi 4B (2 GB or more recommended), RJ45 cable, box/router
• Official 5.1 V 3 A power supply
• A computer with an SSH client

Complete code

# Cote Pi : activer SSH (sudo raspi-config -> Interface Options -> SSH) puis :
ip -br addr                       # noter l'IP de eth0
sudo apt install ethtool iperf3
sudo ethtool eth0                 # Speed: 1000Mb/s attendu
# Benchmark (serveur iperf3 -s sur un PC du meme reseau) :
iperf3 -c 192.168.1.10            # viser ~940 Mbit/s

# Cote PC : connexion et cles
ssh pi@192.168.1.50
ssh-copy-id pi@192.168.1.50       # authentification par cle
scp rapport.txt pi@192.168.1.50:~/

Expected verification

ethtool indicates Speed: 1000Mb/s; iperf3 approaches 940 Mbit/s upstream and downstream, the signature of native GbE (the 3B+ caps out at ~300). After ssh-copy-id, the SSH connection succeeds without a password.

Common errors

• Expecting throughput over Wi-Fi: the Pi's 802.11ac is only class 120 Mb/s, plug in the RJ45.
• Relying on a dynamic IP that changes: reserve the address on the router (static DHCP lease).
• Weak power supply: below 4.63 V the undervoltage detector triggers, causing throttling and SD card corruption.
• Forgetting to enable SSH before unplugging the screen: you then need a screen or to rewrite the SD card.
• Not changing the default password before exposing the machine.