iptables -t nat -i $INCOMING_DEV -p $PROTO --dport 12345 -j
DNAT --to $INTERN_HOST
That won't work, it's missing the chain (-[A|I] PREROUTING). Otherwise, I
guess it's OK. You can DNAT to a specific target port as well, if you want,
I believe.
Cheers,
Tobias