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CJDNS NAT Gateway

Guide courtesy of hyperboria.name with minor edits.

Configure a host to act as a NAT gateway to provide access to Hyperboria for devices on your LAN (Windows PC, tablet, smart phone).

This is a guide to setting up Ubuntu 13.04 to act as an IPv6 router and NAT gateway for CJDNS. Those who prefer other distros should find it trivial to adapt these instructions as required. If you do not have a Linux server on your LAN already, consider purchasing a BeagleBone Black (for only $45 dollars!). You can find instructions here on how to set it up for CJDNS.

WARNING: The built-in security and encryption of CJDNS will NOT carry over past the gateway. Use of a NAT gateway for CJDNS should ONLY be done on a secure and trusted LAN. Any device on the LAN could theoretically intercept local CJDNS traffic before it reaches the gateway, and all devices will appear to other CJDNS nodes to BE the gateway node. This is intended to be a temporary solution until more universal compatibility is available for CJDNS.

You will need:

  • One device running Ubuntu 13.04 and connected to your LAN

OR

  • One device running the Linux of your choice with kernel 3.7 or later and connected to your LAN
  • Sufficient knowledge to adapt this guide to your prefered Linux

Update and Configure iptables

You will find it much easier to do this as root rather then using sudo, so run sudo -i first.

You will need iptables 1.4.17 or better to properly configure IPv6 NAT with masquerade. Unfortunately, the latest Ubuntu as of the writing of this guide (13.04) only has 1.4.12, so you will need to download and install these packages (in order) before continuing:

wget http://ftp.us.debian.org/debian/pool/main/libn/libnfnetlink/libnfnetlink0_1.0.1-2_armhf.deb
dpkg -i libnfnetlink0_1.0.1-2_armhf.deb

wget http://mirrors.kernel.org/debian/pool/main/i/iptables/libxtables10_1.4.18-1_armhf.deb
dpkg -i libxtables10_1.4.18-1_armhf.deb

wget http://mirrors.kernel.org/debian/pool/main/i/iptables/iptables_1.4.18-1_armhf.deb
dpkg -i iptables_1.4.18-1_armhf.deb

Obviously this will not be necessary if you already have iptables 1.4.17 or later installed. You can confirm your version by running the following command:

    iptables --version

Also note that you will need Linux kernel 3.7 or later to have support for IPv6 NAT at all.

Next you need to enable forwarding for IPv6:

echo 1 > /proc/sys/net/ipv6/conf/all/forwarding

Make it permenent by editing /etc/sysctl.conf to include the following line:

net.ipv6.conf.all.forwarding=1

You will most likely find it in there already, but commented out. Simply remove the "#".

Now enter the ip6tables rules:

ip6tables -t nat -A POSTROUTING -o tun0 -j MASQUERADE
ip6tables -A FORWARD -i tun0 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
ip6tables -A FORWARD -i eth1 -o eth0 -j ACCEPT

Or if you use nftables:

nft add rule ip6 nat POSTROUTING oifname "tun0" counter masquerade
nft add rule ip6 filter FORWARD iifname "tun0" oifname "eth0" ct state related,established accept
nft add rule ip6 filter FORWARD iifname "eth1" oifname "eth0" accept

Save the rules:

ip6tables-save > /etc/network/ip6tables.rules

Create the file /etc/network/if-pre-up.d/ip6tables containing the following:

#!/bin/sh
ip6tables-restore < /etc/network/ip6tables.rules
exit 0

And make it executable:

chmod +x /etc/network/if-pre-up.d/ip6tables

Now iptables is configured as an IP v6 NAT gateway, and the settings will be preserved through reboots.

Install and Configure radvd

Install radvd so that your gateway advertises itself on the network:

apt-get install radvd

Create (or edit if already present) the file /etc/radvd.conf with the following contents:

interface eth0
{
    AdvSendAdvert on;
    prefix fdfc::1/64
    {
        AdvRouterAddr on;
    };
};

Note that this assumes you will be using the eth0 interface. If your LAN interface is different, you need to replace eth0 with the correct one.

Start/restart radvd:

/etc/init.d/radvd restart

Now IPv6 capable computers and devices should configure themselves to use your gateway automatically as soon as they are connected to the network.

To ensure proper routing, however, the interface needs the right IP assigned to it. Edit the file /etc/network/interfaces to include the following:

iface eth0 inet6 static
pre-up modprobe ipv6
address fdfc:0000:0000:0000:0000:0000:0000:0001
netmask 64

Once again, this assumes your LAN interface is eth0. Adjust as required. At this point, it is recommended that you reboot so you can confirm everything is still working:

reboot

Don't forget to start CJDNS after it's done booting if you haven't set it up to start automatically. Alternatively, if you do not want to reboot at this time, you can run the following command to assign the IP address to the interface manually:

ip addr add fdfc::1/64 dev eth0

You may need to disconnect and reconnect some devices to get them to autoconfigure, but in most cases you should only need to wait a minute or two for them to work. Other then that, you should be done!