Turn On The Alg; Set Up A Virtual Server Policy For H.323 - ZyXEL Communications ZyWall USG 2000 User Manual

Chapter 6 Tutorials
forward H.323 traffic destined for ge2 IP address 10.0.0.8 to a H.323 device
located on the LAN and using IP address 192.168.1.56.
Figure 83 WAN to LAN H.323 Peer-to-peer Calls Example
192.168.1.56

6.7.1 Turn On the ALG

Click Network > ALG. Select Enable H.323 transformations and click Apply.
Figure 84 Network > ALG

6.7.2 Set Up a Virtual Server Policy For H.323

In this example, you need a virtual server policy to forward H.323 (TCP port 1720)
traffic received on the ZyWALL's 10.0.0.8 WAN IP address to LAN IP address
192.168.1.56.
126
10.0.0.8
ZyWALL USG 2000 User's Guide