D-Link DSR-500, User Manual

Page: 77 / 213

Unified Services Router User Manual
75
Figure 43 : Li st of user def ined services .
5.5 ALG support
Advanced > Firewall Settings > ALGs
Application Level Gateways (ALGs) are security component that enhance the firewall
and NAT support of this router to seamlessly support application layer protocols. In
some cases enabling the ALG will allow the firewall to use dynamic ephemeral TCP/
UDP ports to communicate with the known ports a particular client application (such
as H.323 or RTSP) requires, without which the admin would have to open large
number of ports to accomplish the same support. Because the ALG understands the
protocol used by the specific application that it supports, it is a very secure and
efficient way of introducing support for client applications through the router‘s
firewall.