How to enable Iptables with Netmeeting

Iknownot: just trying to add something to your post, the REDIRECT target is correct.
Redirect is commonly used on transparent proxy. It redirects routed frames to the firewall machine. If i understand correctly, that proxy is running under same linux as iptables and there is no proxy configuration on netmeeting (if there is, i think that is not a "transparent proxy"). If you dont specify any subkeyword on REDIRECT, the port wont be changed (that is the desired behavior).
I still think that a proxy inst necessary on that configuration and just make the thing worst. However im too lazzy to write an entire iptables configuration here :)

This is how i did it. I installed nmproxy on fedora without any problems. Then enabled IP forwarding.

Only had one error cp: cannot stat 'nmproxy.Linux' : No such file or directory
but that was easly fixed by doing this:
cp Makefile.Linux Makefile
make
After that just installed it as usual.

I then opened port 1720 on my firewall.
Net Meeting opens random ports for video and audio so it wont work over a firewall without
some help from nmproxy.

I ran this next:
iptables -A PREROUTING -t nat -p TCP -d $ip_of_your_firewall
--dport 1720 -j DNAT --to $ip_of netmeeting_box:1720

These open needed ports for nmproxy. You need these and you'll find it in nmproxy.conf file:
iptables -I INPUT -p tcp --dport 1720 -j ACCEPT
iptables -I INPUT -p tcp --dport 10200:10209 -j ACCEPT
iptables -I INPUT -p udp --dport 10200:10259 -j ACCEPT

My proxy and my firewall are on different machines. So i copied these specific rules of the web from http://www.cryogenic.net/nmproxy.html#Firewall:

iptables -I PREROUTING -t nat -p tcp --dport 10200:10209 -d $FIREWALL -j DNAT --to-destination $PROXY
iptables -I PREROUTING -t nat -p udp --dport 10200:10259 -d $FIREWALL -j DNAT --to-destination $PROXY
iptables -I PREROUTING -t nat -p tcp --dport 1720 ! -s $PROXY -j DNAT --to-destination $PROXY

In nmproxy.conf i only changed the follwoing line
# default_forward=4.5.6.7
to default_forward=192.168.0.37

Its working fine and it was easy to setup. I think its excellent and easy to use. The only bad thing about nmproxy is that it's not free for commerical use.

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Iknownot: just trying to add something to your post, the REDIRECT target is correct.

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Yes, I believe you are correct. Apparently it is used to intercept all requests to the outside, from inside. I was thinking the other way, since I am used to seeing this with changing the ports from within.

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I still think that a proxy inst necessary on that configuration and just make the thing worst. However im too lazzy to write an entire iptables configuration here

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Remember, one has to consider the firewall used. If default policies are set to deny ( as they should, and not necessarily the default ) it may be more difficult to get this thing working. And the helpers ( sound, etc. ) won't be forwarded with just a NAT of port 1720. ( Again, haven't tried this in years ... but when I did it wouldn't work, thus the necessity of the h323-conntrack-nat - h323 connection tracking and NAT helper .)

As bAgZ confirmed, this is a much simpler way to set something like this up instead of patching Netfilter and the kernel, but I am still concerned with those rules.