How do you troubleshoot network connectivity issues on a Raspberry Pi?

 Troubleshooting network connectivity issues on a Raspberry Pi involves systematic checks across hardware, software, and network configurations. Here’s a step-by-step guide:

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1. Verify Physical Connections

• Ethernet:

  • Ensure the cable is securely plugged into both the Pi and router/switch.

  • Try a different cable or port on the router.

• Wi-Fi:

  • Confirm the Pi’s Wi-Fi antenna (if external) is connected.

  • Check signal strength with:

    bash

    iwconfig wlan0 | grep "Signal"

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2. Check Network Interface Status

• List all interfaces:

  bash

  ip a

  • Look for eth0 (Ethernet) or wlan0 (Wi-Fi). If missing, the driver may not be loaded.

• Bring an interface up/down:

  bash

  sudo ip link set eth0 up  # Enable
  sudo ip link set eth0 down  # Disable

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3. Test DHCP Configuration

• Renew DHCP lease:

  bash

  sudo dhclient -v eth0  # Ethernet
  sudo dhclient -v wlan0  # Wi-Fi

• Check assigned IP:

  bash

  hostname -I  # Quick IP check
  ifconfig eth0 | grep "inet "  # Detailed

  • If no IP is assigned, proceed to manual configuration or check router DHCP settings.

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4. Validate DNS & Internet Access

• Test DNS resolution:

  bash

  ping google.com

  • If DNS fails but IP works (e.g., ping 8.8.8.8 succeeds), fix DNS:

    bash

    echo "nameserver 8.8.8.8" | sudo tee /etc/resolv.conf

• Check default gateway:

  bash

  ip route | grep default

  • If missing, add it manually:

    bash

    sudo route add default gw 192.168.1.1 eth0

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5. Inspect Wi-Fi Configuration

• Scan for networks:

  bash

  sudo iwlist wlan0 scan | grep ESSID

• Verify Wi-Fi credentials in /etc/wpa_supplicant/wpa_supplicant.conf:

  plaintext

  network={
      ssid="Your_SSID"
      psk="Your_Password"
  }

• Reconfigure Wi-Fi:

  bash

  wpa_cli -i wlan0 reconfigure

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6. Check Firewall & Services

• Disable firewall temporarily:

  bash

  sudo ufw disable

• Restart networking services:

  bash

  sudo systemctl restart networking  # Ethernet
  sudo systemctl restart wpa_supplicant  # Wi-Fi

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7. Review System Logs

• Check kernel messages:

  bash

  dmesg | grep eth0  # Ethernet
  dmesg | grep wlan0  # Wi-Fi

• Network service logs:

  bash

  journalctl -u networking --no-pager

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8. Test Alternative Hardware

• Use a USB-to-Ethernet adapter or USB Wi-Fi dongle to rule out hardware failure.

• For Wi-Fi issues, try 5GHz bands (if supported) to avoid interference.

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9. Reinstall/Update Drivers

• Update packages and firmware:

  bash

  sudo apt update && sudo apt full-upgrade
  sudo rpi-update  # Update kernel/firmware

• Reinstall Wi-Fi drivers:

  bash

  sudo apt reinstall firmware-brcm80211

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10. Reset Network Configuration

• Revert to default settings:

  bash

  sudo rm /etc/network/interfaces.d/*  # Remove custom configs
  sudo cp /etc/network/interfaces{.bak,}  # Restore backup (if any)

• Reboot:

  bash

  sudo reboot

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Common Issues & Fixes

Symptom	Likely Cause	Solution
No IP address	DHCP failure	Manually assign IP or check router DHCP
Can ping IPs but not URLs	DNS misconfiguration	Set DNS in /etc/resolv.conf
Wi-Fi disconnects	Power saving mode	Disable with iwconfig wlan0 power off
Slow speeds	Interference/congestion	Switch Wi-Fi bands (2.4GHz → 5GHz)
Interface not detected	Driver/hardware issue	Test USB adapter or update kernel

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Final Checks

1. Compare with another device: Verify if the issue is Pi-specific or network-wide.

2. Test with a fresh OS: Boot a minimal Raspberry Pi OS image to rule out software corruption.

By following these steps, you can isolate and resolve most network issues on a Raspberry Pi. For persistent problems, consult the official Raspberry Pi forums.