Yggdrasil only router configuration - PurpleI2P/i2pd GitHub Wiki

For a router talking to other routers and reseed servers through Yggdrasil only.
Start yggdrasil first. Create ~/.i2pd/i2pd.conf

daemon=true
ipv4=false
ipv6=false
ssu=false
ntcp2.enabled=false
ssu2.enabled=false
meshnets.yggdrasil=true  

If you use Yggdrasil subnet and want to bind your router to a particular address specify it with
meshnets.yggaddress= your local yggdrasil address

Start i2pd, it will also reseed from an yggdrasil reseed server. No clearnet communication is involved.