Ericsson W21 - Manual (Page 45)

Configuration and Management
applications and the local network. When UPnP IGD is enabled, programs
like MSN Messenger
®
and most network enabled games are allowed to
pass the NAT service.
UPnP IGD is enabled by default, but if you want to disable the feature, clear
the “Enable UPnP IGD” check box and click
Apply to save the setting.
2.7.2 Application Level Gateways
From a security perspective, certain Internet applications, for example FTP
applications that open additional ports upon transfer, are especially
problematic to handle. An Application Level Gateway (ALG) provides a
translation and transportation service for such a specific application.
Incoming data packets are checked against existing NAT and packet
filtering rules, IP addresses are evaluated and a detailed packet analysis is
performed. If necessary, the contents of a packet are modified and if a
secondary port is required, the ALG will open one. The Ericsson W21
includes ALG support for the following applications:
Table 14 - ALG Supported applications
Application Protocol Port
number
File Transfer Protocol (FTP) TCP 21
Trivial File Transfer Protocol (TFTP) UDP 69
The ALG for each application does not require additional configuration. The
supported ALGs can be enabled and disabled individually.
To disable an ALG, clear the corresponding check box and click Apply to
save the settings.
2.7.3 Port Forwarding
Port forwarding is used to allow an external user to access a service
residing on a server connected to the LAN (to cross the NAT border). It
enables access to servers on the LAN from the Internet (e.g. Web server)
and also enables applications to work from the LAN (e.g. games, voice and
chat) to the Internet.
Note: Port forwarding requires a public IP address of the Ericsson
W21. This IP address is displayed on the Overview page as the
“Internet: IP address”. A private IP address usually begins with 10,
172
, or 192. In this case, no incoming access from the Internet is
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