You could try :
iptables -I INPUT -p udp --dport ( insert the port number here) -j ACCEPT
So, thats --dport ( for the destination ) and --sport (for the source)
In my experience, the command to change a port has not changed from distro to distro.
NOTE: I am finding these sites to be very informative for my own uses:
some neat port connection rate / limit examples
some neat logging examples
Hope this stuff helps. see ya!