To communicate using a tool like Microsoft NetMeeting or GnomeMeeting through a Linux (kernel 2.4.x-based) firewall, you have to redirect some ports to one IP address in the inside network, otherwise, it won't work.
Here is a little script meant to achieve exactly that:
#!/bin/sh # Script to redirect H.323 trafic to one specific IP behind the firewall IPTABLES=/sbin/iptables OUT_DEV=ppp0 IN_HOST=192.168.11.33 TCP_PORT_RANGE=30000:30010 UDP_PORT_RANGE=5000:5003 TCP_LISTENING_PORT=1720 #$IPTABLES -t nat -A POSTROUTING -o $OUT_DEV -j MASQUERADE $IPTABLES -t nat -A PREROUTING -i $OUT_DEV -p tcp --dport $TCP_PORT_RANGE -j DNAT --to-dest $IN_HOST $IPTABLES -t nat -A PREROUTING -i $OUT_DEV -p udp --dport $UDP_PORT_RANGE -j DNAT --to-dest $IN_HOST $IPTABLES -A FORWARD -p tcp -i $OUT_DEV --dport $TCP_PORT_RANGE -d $IN_HOST -j ACCEPT $IPTABLES -A FORWARD -p udp -i $OUT_DEV --dport $UDP_PORT_RANGE -d $IN_HOST -j ACCEPT $IPTABLES -t nat -A PREROUTING -i $OUT_DEV -p tcp --dport $TCP_LISTENING_PORT -j DNAT --to-dest $IN_HOST $IPTABLES -A FORWARD -p tcp -i $OUT_DEV --dport $TCP_LISTENING_PORT -d $IN_HOST -j ACCEPTYou have of course to modify the variables at the beginning to suit your particuliar setup. This one works for a bunch of Debian-based installs with ADSL connection.
This article was first written in October 2003 for the BeezNest technical website (http://glasnost.beeznest.org/articles/75)
