blog post internet sharing

source/_posts/2014-02-08-internet-sharing-ipv4-and-ipv6-on-archlinux-using-dnsmasq.markdown

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+---
+layout: post
+title: "Internet sharing (ipv4 and ipv6) on archlinux using dnsmasq"
+date: 2014-02-08 20:02:22 +0100
+comments: true
+categories:
+- arch
+- dhcp
+- ipv6 router advertisement
+---
+
+A guide to connect with a different machine using a ethernet cable for
+internet sharing or just transferring files:
+
+1. Install dnsmasq and iproute2
+
+    $ pacman -S dnsmasq iproute2
+
+2. Copy over the configuration files at the end of the article and edit the
+   */etc/conf.d/share-internet* to match your network setup.
+
+3. 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!
+
+{% include_code /etc/conf.d/share-internet lang:bash share-internet/share-internet %}
+
+{% include_code /etc/systemd/system/share-internet.service lang:ini share-internet/share-internet.service %}
+
+{% include_code /etc/dnsmasq.conf lang:ini share-internet/dnsmasq.conf %}
+
+{% include_code /etc/dnsmasq.conf.dhcp lang:bash share-internet/dnsmasq.conf.dhcp %}

source/downloads/code/share-internet/dnsmasq.conf

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+# google as an upstream dns server
+server=8.8.8.8
+server=8.8.4.4
+no-resolv
+cache-size=2000
+
+#conf-file=/etc/dnsmasq.conf.dhcp

source/downloads/code/share-internet/dnsmasq.conf.dhcp

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+# no need to modify
+# ingoing and outgoing device will be set by the systemd service
+interface=enp0s25
+no-dhcp-interface=wlp3s0
+dhcp-range=10.20.0.100,10.20.0.199,infinite
+dhcp-option=3,10.20.0.1  # router
+dhcp-option=5,10.20.0.1  # dns
+dhcp-option=42,10.20.0.1 # ntp
+dhcp-range=fd21:30c2:dd2f::,ra-stateless,ra-names,infinite
+enable-ra

source/downloads/code/share-internet/share-internet

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+# Network device where other hosts are connect to, ex: eth0
+INTERNAL_DEVICE="enp0s25"
+# Device which has internet access, ex: wlan0 or usb0
+EXTERNAL_DEVICE="wlp3s0"

source/downloads/code/share-internet/share-internet.service

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+[Unit]
+Description='share internet'
+
+[Service]
+Type=oneshot
+EnvironmentFile=/etc/conf.d/share-internet
+RemainAfterExit=yes
+ExecStart=/usr/bin/sed -ie 's!^#conf-file=/etc/dnsmasq\.conf\.dhcp!conf-file=/etc/dnsmasq.conf.dhcp!' /etc/dnsmasq.conf
+ExecStart=/usr/bin/sed -ie 's/^interface=[[:alnum:]]+/interface=$INTERNAL_DEVICE/' /etc/dnsmasq.conf.dhcp
+ExecStart=/usr/bin/sed -ie 's/^no-dhcp-interface=[[:alnum:]]+/no-dhcp-interface=$EXTERNAL_DEVICE/' /etc/dnsmasq.conf.dhcp
+ExecStart=/usr/bin/iptables -t nat -A POSTROUTING -o $EXTERNAL_DEVICE -j MASQUERADE
+ExecStart=/usr/bin/ip6tables -t nat -A POSTROUTING -o $EXTERNAL_DEVICE -j MASQUERADE
+ExecStart=/usr/bin/sysctl -w net.ipv4.ip_forward=1 net.ipv6.conf.all.forwarding=1
+ExecStart=/usr/bin/ip addr add 10.20.0.1/24 dev $INTERNAL_DEVICE
+ExecStart=/usr/bin/ip addr add fd21:30c2:dd2f::1/64 dev $INTERNAL_DEVICE
+ExecStart=/usr/bin/systemctl restart dnsmasq
+
+ExecStop=/usr/bin/ip addr del 10.20.0.1/24 dev $INTERNAL_DEVICE
+ExecStop=/usr/bin/ip addr del fd21:30c2:dd2f::1/64 dev $INTERNAL_DEVICE
+ExecStop=/usr/bin/sysctl -w net.ipv4.ip_forward=0 net.ipv6.conf.all.forwarding=0
+ExecStop=/usr/bin/iptables -t nat -D POSTROUTING -o $EXTERNAL_DEVICE -i $INTERNAL_DEVICE -j MASQUERADE
+ExecStop=/usr/bin/ip6tables -t nat -D POSTROUTING -o $EXTERNAL_DEVICE -i $INTERNAL_DEVICE -j MASQUERADE
+ExecStop=/usr/bin/sed -ie 's!^conf-file=/etc/dnsmasq\.conf\.dhcp!#conf-file=/etc/dnsmasq.conf.dhcp!' /etc/dnsmasq.conf
+ExecStop=/usr/bin/systemctl restart dnsmasq
+
+[Install]
+WantedBy=multi-user.target