08 Feb 2014

Internet Sharing Ipv4 and Ipv6 on Archlinux Using Dnsmasq

Update: Added adhoc wlan network

A guide to connect with a different machine using a ethernet cable for internet sharing or just transferring files:

Install dnsmasq and iproute2
$ pacman -S dnsmasq iproute2
Copy over the configuration files at the end of the article and edit the /etc/conf.d/share-internet@<device> to match your network setup. (where <device> is your network device)
Start the sharing service with systemd
$ sudo systemctl start internet-sharing@.service

After that the other machine can connect via dhcp. It will get an ipv4 address from the 10.20.0.0/24 subnet and a ipv6 address from the fd21:30c2:dd2f:: subnet. Your host will be reachable via 10.20.0.1 or fd21:30c2:dd2f::1. Thanks to ipv6 router advertising, an AAAA record for each host is automatically set based on the hostname. This means if your hostname is foo, all members of the network can just connect to it using the address foo. You should disable the share-internet.service, if you don’t need it. Otherwise you might mess up network setups, if you connect to a network with the device on which the dhcp service is running.

Happy networking!

# google as an upstream dns server
server=8.8.8.8
server=8.8.4.4
no-resolv
cache-size=2000

Ethernet to Wlan:

# Device which has internet access, ex: wlan0 or usb0
EXTERNAL_DEVICE="wlp3s0"

IP4_ADDRESS="10.20.0.1"
IP4_NETMASK="24"
IP4_SUBNET="10.20.0.2,10.20.0.255"

IP6_ADDRESS="fd21:30c2:dd2f::1"
IP6_NETMASK="64"
IP6_SUBNET="fd21:30c2:dd2f::"

Wlan to Ethernet:

If you have luck and your wifi driver is capable of the infrastructure mode, you should take a look at hostadp, in my case I have to create an adhoc network. To enable the adhoc network:

$ sudo systemctl enable wireless-adhoc@<device>.service

# Device which has internet access, ex: wlan0 or usb0
EXTERNAL_DEVICE="enp0s20u2"

IP4_ADDRESS="10.20.0.1"
IP4_NETMASK="24"
IP4_SUBNET="10.20.0.100,10.20.0.199"

IP6_ADDRESS="fd21:30c2:dd2f::1"
IP6_NETMASK="64"
IP6_SUBNET="fd21:30c2:dd2f::"

[Unit]
Description=Ad-hoc wireless network connectivity (%i)
Wants=network.target
Before=network.target
Conflicts=netctl-auto@.service
BindsTo=sys-subsystem-net-devices-%i.device
After=sys-subsystem-net-devices-%i.device

[Service]
Type=simple
ExecStartPre=/usr/bin/rfkill unblock wifi
ExecStart=/usr/sbin//wpa_supplicant -D nl80211,wext -c/etc/wpa_supplicant/wpa_supplicant-adhoc-%I.conf -i%I

[Install]
RequiredBy=share-internet@%i.service

ctrl_interface=DIR=/run/wpa_supplicant GROUP=wheel

# use 'ap_scan=2' on all devices connected to the network
ap_scan=2

network={
    ssid="The.Secure.Network"
    mode=1
    frequency=2432
    proto=WPA
    key_mgmt=WPA-NONE
    pairwise=NONE
    group=TKIP
    psk="fnord"
}

# MacOS X and Networmanager aren't capable of using WPA/WPA2 for Adhoc Networks
#network={
#    ssid="The.Insecure.Network"
#    mode=1
#    frequency=2432
#    proto=WPA
#    key_mgmt=NONE
#    pairwise=NONE
#    group=TKIP
#
#    wep_key0="fnord"
#    wep_tx_keyidx=0
#}