IPv6

Running FreeBSD 13.3-RELEASE-p1
If no data has been exchanged via a TCP connection for 15 minutes, or if 
no data has been exchanged via a UDP connection for 5 minutes,
my FRITZ!Box router automatically removes the connection(s) in question 
from the NAT table ( "NAT Timeout"). This will close all ports used by 
these connections and disconnect the application (read in this case: 
FreeBSD) from the Internet. According to the manufacturer 'to ensures 
the security of devices in the router's home network and to prevent 
performance losses during Internet access.

This forces me into running an 'IPv6 stay alive' script every 30 minutes 
in order to be available for incoming IPv6 connections. Is there a way 
to use FreeBSD in a more smooth way to tackle this or does the 
manufacturer AVM need to include this functionallity into their hardware?

Thanks, Jos