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[Memo] Using Raspberry Pi 3 as a Wireless Router

Translated by DeepSeek V4 Pro. Translations can be inaccurate, please refer to the original post for important stuff.

Jianlin Su April 12, 2016 #3728

The Raspberry Pi 3, released in early March, comes with built-in WiFi and Bluetooth. Since it already has an Ethernet port, it is essentially a wireless router. I couldn’t help but get one, intending to use it as a router and NAS. There are already many tutorials on making a router with a Raspberry Pi, mostly based on the Raspberry Pi 2. Versions before the 3 did not have built-in WiFi, so you needed to configure a wireless network card yourself. Since the 3 has built-in WiFi, configuration is much more convenient. I successfully configured it by referring to two foreign tutorials and am recording it here.

Reference tutorials:

Configuring the Wireless Hotspot

The main software used are hostapd and dnsmasq:

sudo apt-get install hostapd dnsmasq

Then add the following to the end of /etc/dnsmasq.conf (modify the IP and network segment yourself; this file already exists and is a very detailed configuration file, but all lines are commented out with #):

interface=wlan0
dhcp-range=10.0.0.2,10.0.0.5,255.255.255.0,12h

Then create a new file /etc/hostapd/hostapd.conf and add:

interface=wlan0
hw_mode=g
channel=10
auth_algs=1
wpa=2
wpa_key_mgmt=WPA-PSK
wpa_pairwise=CCMP
rsn_pairwise=CCMP
wpa_passphrase=your_wifi_password
ssid=your_wifi_name

Next, modify /etc/sysctl.conf and change (if this line exists, just remove the #):

net.ipv4.ip_forward=1

Finally, add the following script before exit 0 in /etc/rc.local:

ifconfig wlan0 down
ifconfig wlan0 10.0.0.1 netmask 255.255.255.0 up
iwconfig wlan0 power off
service dnsmasq restart
hostapd -B /etc/hostapd/hostapd.conf & > /dev/null 2>&1
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE  
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

After restarting, you can see the hotspot. It’s much simpler  The WiFi signal strength of the Raspberry Pi is similar to the once-famous router toy WR703N.

Pitfalls and Solutions

I also configured offline downloading, NAS, automatic cloud synchronization, etc. Since I am not very familiar with Linux, I fell into many traps. I want to remind everyone that many commands on the Raspberry Pi need to start with sudo, and sudo on the Raspberry Pi does not require a password. However, having sudo and not having sudo are two completely different environments (two different users). For example, after sudo screen -S sync, you cannot see it with screen -ls; you must use sudo screen -ls to see it. Additionally, if you add commands to /etc/rc.local to run, they are executed as sudo by default (regardless of whether you added sudo). As a result, I added a screen task here, and after starting, I couldn’t see it with screen -ls no matter what. It turned out I needed sudo screen -ls, I’m dizzy... Also, when running autossh for intranet penetration, you must add a sleep 5 command before autossh, otherwise autossh won’t work even if it runs  

These were all traps I fell into for a whole day.

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