We have a MCU 3510 w/GK enabled. I'd like the ability to do calls with people on the Internet, so I put it on my DMZ located off my PIX. I haven't yet tried allowing external (i.e. Internet) people connect, but when I have two internal NetMeeting clients connect, they don't see the video broadcast. If I move the MCU inside, it does work. Both internal clients can see the MCU and register with the gatekeeper. Any idea why they're not seeing one another's video?
I will send you a white paper that covers this issue: in short I would suggest using the MCM gatekeeper proxy and using the proxy as a single access point throught the firewall.