ZyWALL 2 Plus User’s Guide
411
C
H A P T E R
24
ALG Screen
This chapter covers how to use the ZyWALL’s ALG feature to allow certain applications to
pass through the ZyWALL.
24.1 ALG Introduction
An Application Layer Gateway (ALG) manages a specific protocol (such as SIP, H.323 or
FTP) at the application layer. The ZyWALL can function as an ALG to allow certain NAT un-
friendly applications (such as SIP) to operate properly through the ZyWALL.
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 examines and uses
IP address and port number information embedded in the data stream. When a device behind
the ZyWALL uses an application for which the ZyWALL has ALG service enabled, the
ZyWALL translates the device’s private IP address inside the data stream to a public IP
address. It also records session port numbers and dynamically creates implicit NAT port
forwarding and firewall rules for the application’s traffic to come in from the WAN to the
LAN.
24.1.1 ALG and NAT
The ZyWALL dynamically creates an implicit NAT session for the application’s traffic from
the WAN to the LAN.
The ALG on the ZyWALL supports all NAT mapping types, including
One to One
,
Many to
One
,
Many to Many Overload
and
Many One to One
.
24.1.2 ALG and the Firewall
The ZyWALL uses the dynamic port that the session uses for data transfer in creating an
implicit temporary firewall rule for the session’s traffic. The firewall rule only allows the
session’s traffic to go through in the direction that the ZyWALL determines from its
inspection of the data payload of the application’s packets. The firewall rule is automatically
deleted after the application’s traffic has gone through.
Summary of Contents for ADSL 2+ Security Gateway
Page 2: ......
Page 25: ...Table of Contents ZyWALL 2 Plus User s Guide 25 Index 679 ...
Page 26: ...Table of Contents ZyWALL 2 Plus User s Guide 26 ...
Page 46: ...46 ...
Page 88: ...Chapter 3 Wizard Setup ZyWALL 2 Plus User s Guide 88 ...
Page 132: ...132 ...
Page 144: ...Chapter 6 LAN Screens ZyWALL 2 Plus User s Guide 144 ...
Page 180: ...Chapter 9 DMZ Screens ZyWALL 2 Plus User s Guide 180 ...
Page 190: ...190 ...
Page 222: ...Chapter 11 Firewall ZyWALL 2 Plus User s Guide 222 ...
Page 252: ...Chapter 13 Content Filtering Reports ZyWALL 2 Plus User s Guide 252 ...
Page 328: ...Chapter 16 Authentication Server ZyWALL 2 Plus User s Guide 328 ...
Page 330: ...330 ...
Page 346: ...Chapter 17 Network Address Translation NAT ZyWALL 2 Plus User s Guide 346 ...
Page 350: ...Chapter 18 Static Route ZyWALL 2 Plus User s Guide 350 ...
Page 398: ...Chapter 21 Remote Management ZyWALL 2 Plus User s Guide 398 ...
Page 416: ...Chapter 24 ALG Screen ZyWALL 2 Plus User s Guide 416 ...
Page 417: ...417 PART V Logs and Maintenance Logs Screens 419 Maintenance 447 ...
Page 418: ...418 ...
Page 423: ...Chapter 25 Logs Screens ZyWALL 2 Plus User s Guide 423 Figure 274 LOGS Log Settings ...
Page 466: ...466 ...
Page 474: ...Chapter 27 Introducing the SMT ZyWALL 2 Plus User s Guide 474 ...
Page 496: ...Chapter 30 LAN Setup ZyWALL 2 Plus User s Guide 496 ...
Page 504: ...Chapter 32 DMZ Setup ZyWALL 2 Plus User s Guide 504 ...
Page 508: ...Chapter 33 Wireless Setup ZyWALL 2 Plus User s Guide 508 ...
Page 556: ...Chapter 38 Filter Configuration ZyWALL 2 Plus User s Guide 556 ...
Page 570: ...Chapter 40 System Information Diagnosis ZyWALL 2 Plus User s Guide 570 ...
Page 586: ...Chapter 41 Firmware and Configuration File Maintenance ZyWALL 2 Plus User s Guide 586 ...
Page 594: ...Chapter 42 System Maintenance Menus 8 to 10 ZyWALL 2 Plus User s Guide 594 ...
Page 598: ...Chapter 43 Remote Management ZyWALL 2 Plus User s Guide 598 ...
Page 604: ...604 ...
Page 612: ...Chapter 45 Troubleshooting ZyWALL 2 Plus User s Guide 612 ...
Page 620: ...620 ...
Page 644: ...Appendix B Pop up Windows JavaScripts and Java Permissions ZyWALL 2 Plus User s Guide 644 ...
Page 668: ...Appendix E Importing Certificates ZyWALL 2 Plus User s Guide 668 ...
Page 672: ...Appendix F Legal Information ZyWALL 2 Plus User s Guide 672 ...
Page 678: ...Appendix G Customer Support ZyWALL 2 Plus User s Guide 678 ...