How to configure an embedded Linux board (Colibri VF61) as a WiFi access point using hostapd, udhcpd, and iptables.

Test Setup#

  • Colibri VF61 V1.1A
  • Colibri Evaluation Board V3.1a / Iris V1.1
  • Ambicom WL250N-USB (Ralink RT3070 chipset)

Steps Overview#

  1. Assign a static IP to wlan0
  2. Configure udhcpd as the DHCP server
  3. Configure hostapd as the AP daemon
  4. Enable IP forwarding and NAT between wlan0 and eth0
  5. Wire it all up with systemd service files

1. Static IP for wlan0# 

ifconfig wlan0 192.168.0.1 up

2. udhcpd configuration#

/etc/udhcpd.conf:

start           192.168.0.20
end             192.168.0.254
interface       wlan0
remaining       yes
lease_file      /var/lib/misc/udhcpd.leases
pidfile         /var/run/udhcpd.pid
opt dns         8.8.8.8 8.8.4.4
opt router      192.168.0.1
opt subnet      255.255.255.0
opt lease       864000

3. hostapd configuration#

/etc/hostapd.conf:

interface=wlan0
driver=nl80211
ssid=MyEmbeddedAP
hw_mode=g
channel=6
macaddr_acl=0
auth_algs=1
wpa=2
wpa_key_mgmt=WPA-PSK
wpa_passphrase=your-passphrase
wpa_pairwise=TKIP
rsn_pairwise=CCMP

4. IP forwarding and NAT# 

# Enable forwarding
sysctl -w net.ipv4.ip_forward=1
# Uncomment net.ipv4.ip_forward=1 in /etc/sysctl.conf to persist

# NAT rule
iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -A FORWARD -i wlan0 -o eth0 -j ACCEPT

# Save
iptables-save > /etc/iptables.ipv4.nat

5. systemd service#

/etc/systemd/system/access-point.service:

[Unit]
Description=WiFi Access Point
BindsTo=sys-subsystem-net-devices-wlan0.device
After=sys-subsystem-net-devices-wlan0.device

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/bin/ip link set dev wlan0 up
ExecStart=/bin/ip addr add 192.168.0.1/24 broadcast 192.168.0.255 dev wlan0
ExecStart=/usr/sbin/hostapd -B /etc/hostapd.conf
ExecStart=/usr/sbin/udhcpd -fS /etc/udhcpd.conf
ExecStop=/sbin/ip addr flush dev wlan0
ExecStop=/sbin/ip link set dev wlan0 down

[Install]
WantedBy=multi-user.target

systemctl enable access-point.service
systemctl enable iptables-restore.service