I don't know, and I wouldn't know how to do that either. In the end I found out that if I monitored the dhcp6c.log file on my router and tried different PD size

I don't know, and I wouldn't know how to do that either. In the end I found out that if I monitored the dhcp6c.log file on my router and tried different PD sizes I could see whether it was working or not.