ZyWALL / USG (ZLD) CLI Reference Guide
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ALG
This chapter covers how to use the ZyWALL / USG’s ALG feature to allow certain applications to
pass through the ZyWALL / USG.
21.1 ALG Introduction
The ZyWALL / USG can function as an Application Layer Gateway (ALG) to allow certain NAT un-
friendly applications (such as SIP) to operate properly through the ZyWALL / USG’s NAT.
Some applications cannot operate through NAT (are NAT un-friendly) because they embed IP
addresses and port numbers in their packets’ data payload. The ZyWALL / USG examines and uses
IP address and port number information embedded in the VoIP traffic’s data stream. When a device
behind the ZyWALL / USG uses an application for which the ZyWALL / USG has VoIP pass through
enabled, the ZyWALL / USG translates the device’s private IP address inside the data stream to a
public IP address. It also records session port numbers and allows the related sessions to go
through the firewall so the application’s traffic can come in from the WAN to the LAN.
The ZyWALL / USG only needs to use the ALG feature for traffic that goes through the ZyWALL /
USG’s NAT. The firewall allows related sessions for VoIP applications that register with a server. The
firewall allows or blocks peer to peer VoIP traffic based on the firewall rules.
You do not need to use a TURN (Traversal Using Relay NAT) server for VoIP devices behind the
ZyWALL / USG when you enable the SIP ALG.
Summary of Contents for ZyWALL USG Series
Page 19: ...19 PART I Introduction ...
Page 20: ...20 ...
Page 38: ...Chapter 2 User and Privilege Modes ZyWALL USG ZLD CLI Reference Guide 38 ...
Page 39: ...39 PART II Reference ...
Page 40: ...40 ...
Page 48: ...Chapter 4 Status ZyWALL USG ZLD CLI Reference Guide 48 ...
Page 52: ...Chapter 5 Registration ZyWALL USG ZLD CLI Reference Guide 52 ...
Page 128: ...Chapter 15 Route ZyWALL USG ZLD CLI Reference Guide 128 ...
Page 136: ...Chapter 17 Zones ZyWALL USG ZLD CLI Reference Guide 136 ...
Page 140: ...Chapter 18 DDNS ZyWALL USG ZLD CLI Reference Guide 140 ...
Page 148: ...Chapter 20 HTTP Redirect ZyWALL USG ZLD CLI Reference Guide 148 ...
Page 152: ...Chapter 21 ALG ZyWALL USG ZLD CLI Reference Guide 152 ...
Page 156: ...Chapter 22 UPnP ZyWALL USG ZLD CLI Reference Guide 156 ...
Page 159: ...Chapter 23 IP MAC Binding ZyWALL USG ZLD CLI Reference Guide 159 ...
Page 178: ...Chapter 25 Secure Policy ZyWALL USG ZLD CLI Reference Guide 178 ...
Page 218: ...Chapter 32 Application Patrol ZyWALL USG ZLD CLI Reference Guide 218 ...
Page 236: ...Chapter 34 IDP Commands ZyWALL USG ZLD CLI Reference Guide 236 ...
Page 246: ...Chapter 35 Content Filtering ZyWALL USG ZLD CLI Reference Guide 246 ...
Page 256: ...Chapter 36 Anti Spam ZyWALL USG ZLD CLI Reference Guide 256 ...
Page 262: ...Chapter 37 SSL Inspection ZyWALL USG ZLD CLI Reference Guide 262 ...
Page 268: ...Chapter 38 Device HA ZyWALL USG ZLD CLI Reference Guide 268 ...
Page 284: ...Chapter 41 Addresses ZyWALL USG ZLD CLI Reference Guide 284 ...
Page 288: ...Chapter 42 Services ZyWALL USG ZLD CLI Reference Guide 288 ...
Page 302: ...Chapter 46 Authentication Server ZyWALL USG ZLD CLI Reference Guide 302 ...
Page 338: ...Chapter 52 System Remote Management ZyWALL USG ZLD CLI Reference Guide 338 ...
Page 358: ...Chapter 53 File Manager ZyWALL USG ZLD CLI Reference Guide 358 ...
Page 372: ...Chapter 56 Session Timeout ZyWALL USG ZLD CLI Reference Guide 372 ...
Page 374: ...Chapter 57 Diagnostics ZyWALL USG ZLD CLI Reference Guide 374 ...
Page 384: ...Chapter 59 Maintenance Tools ZyWALL USG ZLD CLI Reference Guide 384 ...
Page 426: ...List of Commands Alphabetical ZyWALL USG ZLD CLI Reference Guide 426 ...