What is yggdrasil

Recently yggdrasil got my interest after playing around with wireguard then tailscale.

I was in the right mood when I read a blogpost by John Goerzen about yggdrasil

In short: yggdrasil is an overlay network. You generate a private key then you get your own stable and presistent ipv6 address (which is available within the network you join or create).

yggdrasil networks

There are two kind of addresses you can get. One is a single ipv6 address from 200::/7. There is an optional network associated with the former from 300::/7, but instead of a single address it is a ::/64

If you have printers or other stuff available on that network that you cannot or do not want to run the yggdrasil daemon on you can advertise this network with radvd:

interface eth0
     AdvSendAdvert on;
     AdvDefaultLifetime 0;
     prefix 300:1111:2222:3333::/64 {
         AdvOnLink on;
         AdvAutonomous on;
     route 200::/7 {};

but openwrt deprecated radvd (in favor of odhcpd) some time ago this means it is not available for install. How to do this on openwrt then? let's find out!


Recent versions of openwrt includes yggdrasil thus installation is not an issue. There is a lua module so it can be poked from the luci webui.

A new interface shows up with the name yggdrasil. As I accept no external peers other than the ones I control I put it into the lan zone in /etc/config/firewall:

config zone
    option name 'lan'
    list network 'lan'
    list network 'yggdrasil'

then I created ygglan as an alias interface in /etc/config/network:

config interface 'ygglan'
    option proto 'static'
    list ip6addr '300:1111:2222:3333::1/64'
    option ip6prefix '300:1111:2222:3333::/64'
    option device 'br-lan'

No this is not the same as in the radvd example as I was unable to figure out how to announce a custom route. I am using for my benefit that openwrt already advertises a default route for ipv6. (If there is an issue with ipv6 and openwrt stops advertising a default route then yggdrasil breaks as well as a result.)