TMS zl Management and Configuration Guide ST.1.1.100226

4-87

Firewall

Application-Level Gateways (ALGs)

The TMS zl Module supports ALGs for several common applications that can

experience difficulties when they run through a firewall. These ALGs help the

applications to run smoothly through the TMS zl Module firewall without

compromising security. For example, some applications open data-transfer

connections dynamically by negotiating IP addresses and service ports. An

ALG allows such an application with the opening of a single control port. ALGs

provide other special handling for applications which you can read about in

the sections below.

Refer to these sections according to your interests:

■ For background information on ALGs, see “ALG Concepts” on page 4-87.

■ To learn more about the specific TMS zl Module ALGs, see “ALG Descrip-

tions” on page 4-90.

■ To learn how to enable and disable ALGs, see “Enable and Disable

Optional Attack Checks” on page 4-110.

ALG Concepts

Table 4-12 shows the ALGs supported by the TMS zl Module. The FTP ALG is

enabled by default; all other ALGs are disabled by default. In addition to listing

the ALGs by name, the table provides this information for each ALG:

■ Control port

See “Control Port” on page 4-88 for an explanation of why you need to

know about the control port.

■ ALG type

See “ALG Types” on page 4-89 for an explanation of the types of support

provided by ALGs.