curl -s 'https://myname:email@example.com/nic/update?hostname=123456'
You have to run this from a machine on your LAN
I created a script like this
date >> /var/log/tunnelbroker.log
curl -s 'https://myname:firstname.lastname@example.org/nic/update?hostname=123456' >> /var/log/tunnelbroker.log
and put it into my crontab. Problem solved!
Thanks to the Tunnelbroker FAQ:
My IPv4 endpoint address is dynamic. Can I still create a tunnel? If yes, what do I need to do when my IP address changes?
Yes, you can still create a tunnel even if you are using a dynamic IPv4 endpoint address. If your IPv4 endpoint address changes, you can either login to the tunnelbroker.net page and update your IPv4 endpoint address or use https://ipv4.tunnelbroker.net/nic/update which is designed to be used to update your IPv4 endpoint address.