DIY

Minimal Guide to Configure Raspberry Pi as a Wireless Router

Step-by-step guide to configure Raspberry Pi as a wireless router with access point and network forwarding capabilities

Minimal Guide to Configure Raspberry Pi as a Wireless Router

0. Prerequisites

Hardware Environment: Raspberry Pi 3 B+ (compatible with other models)

Software Environment: Raspberry Pi Official 32-bit OS, recommended to change software sources for faster downloads.

Change Software Sources

sudo vim /etc/apt/sources.list

Comment out original sources and add Tsinghua sources:

deb http://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ buster main non-free contrib
deb-src http://mirrors.tuna.tsinghua.edu.cn/raspbian/raspbian/ buster main non-free contrib

sudo vim /etc/apt/sources.list.d/raspi.list

Add:

deb http://mirrors.tuna.tsinghua.edu.cn/raspberrypi/ buster main ui

Update package list:

sudo apt update

1. Install Required Software

sudo apt install dnsmasq hostapd
  • dnsmasq: Provides DNS and DHCP services
  • hostapd: Configures wireless card as Access Point

2. Configure Network Interfaces

sudo vim /etc/network/interfaces

Add the following configuration at the beginning of the file:

# Ethernet interface configuration
auto eth0
allow-hotplug eth0
iface eth0 inet dhcp

# Wireless interface configuration
allow-hotplug wlan0
iface wlan0 inet static
    address 192.168.2.1
    netmask 255.255.255.0
    network 192.168.2.0
    broadcast 192.168.2.255

# Restore iptables rules on startup
up iptables-restore < /etc/iptables.ipv4.nat

Configuration Notes:

  • eth0: Ethernet interface, set to DHCP for automatic IP acquisition
  • wlan0: Wireless interface, configured with static IP 192.168.2.1
  • After configuration, this wireless interface cannot connect to other WiFi networks
  • Broadcast address: 192.168.2.255, Network address: 192.168.2.0, Subnet mask: 255.255.255.0

3. Configure hostapd (Wireless Access Point)

sudo vim /etc/hostapd/hostapd.conf

Create new file if it doesn’t exist, add the following content:

# Wireless interface name
interface=wlan0

# Use nl80211 driver
driver=nl80211

# Network name (SSID)
ssid=passwd-is-81

# Use 2.4GHz band
hw_mode=g

# Channel
channel=6

# Enable 802.11n
ieee80211n=1

# Enable WMM
wmm_enabled=1

# Enable 40MHz channels
ht_capab=[HT40][SHORT-GI-20][DSSS_CCK-40]

# MAC address access control
macaddr_acl=0

# Authentication algorithms
auth_algs=1

# Hide SSID setting
ignore_broadcast_ssid=0

# Use WPA2
wpa=2

# WPA key management
wpa_key_mgmt=WPA-PSK

# Network passphrase
wpa_passphrase=11111111

# Encryption method
rsn_pairwise=CCMP

Hotspot Information:

  • SSID: passwd-is-81
  • Password: 11111111
  • Band: 2.4GHz

4. Configure dnsmasq (DNS and DHCP)

sudo vim /etc/dnsmasq.conf

If the file has existing content, comment it out and add:

# Use wlan0 interface
interface=wlan0

# Listen address
listen-address=192.168.2.1

# Bind to interface
bind-interfaces

# DNS server
server=114.114.114.114

# Don't forward short names
domain-needed

# Never forward non-routed addresses
bogus-priv

# DHCP address range
dhcp-range=192.168.2.2,192.168.2.254,12h

Important: Ensure IP addresses match the network interface configuration from Step 2.

5. Configure iptables (Network Forwarding)

iptables is Linux’s firewall tool used to configure network packet forwarding rules.

# Set up NAT forwarding
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

# Set up forwarding rules
sudo iptables -A FORWARD -i eth0 -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -i wlan0 -o eth0 -j ACCEPT

# Save rules
sudo sh -c "iptables-save > /etc/iptables.ipv4.nat"

Saved rules will be automatically restored on system startup (via configuration in Step 2).

6. Enable IPv4 Forwarding

sudo vim /etc/sysctl.conf

Find and uncomment (or add):

net.ipv4.ip_forward=1

Or apply immediately:

sudo echo 1 > /proc/sys/net/ipv4/ip_forward

7. Configure Auto-start on Boot

Use systemctl to configure services to start automatically:

sudo systemctl enable dnsmasq
sudo systemctl enable hostapd

If you encounter error Failed to start hostapd.service: Unit hostapd.service is masked., execute:

sudo systemctl unmask hostapd
sudo systemctl enable hostapd

Other Useful Commands:

  • Start services immediately: sudo systemctl start dnsmasq / sudo systemctl start hostapd
  • Check service status: sudo systemctl status dnsmasq / sudo systemctl status hostapd
  • Restart services: sudo systemctl restart dnsmasq / sudo systemctl restart hostapd

Verification

Reboot Raspberry Pi after configuration:

sudo reboot

After reboot, search for WiFi network passwd-is-81 on other devices, connect with password 11111111, and you should be able to connect normally and access the internet.

Troubleshooting

  1. Cannot connect to internet: Check if eth0 obtained IP address normally
  2. Cannot obtain IP address: Check if dnsmasq service is running properly
  3. Cannot find WiFi signal: Check hostapd service status and configuration
  4. No internet after connection: Check iptables rules and IP forwarding settings