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Configuration and Management

4.7.2 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 W25

includes ALG support for the following applications:

Table 4 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 on the

NAT page and click

Apply .

4.7.3 Port Forwarding

Port forwarding (sometimes referred to as tunneling) is used to allow an

external user to reach a port on a private IP address (inside a LAN) from

the outside via a NAT-enabled router (Ericsson W25).

When a computer on the Internet sends data to the public IP address of

Ericsson W25, it needs to know what to do with the data. Port Forwarding

tells Ericsson W25 which computer on the local area network to send the

data to.

Note: Port forwarding requires a public IP address of the Ericsson W25.

The Ericsson W25 IP address is displayed on the

Internet page. A

private IP address usually begins with

10, 172, or 192. In this

case, no incoming access from the Internet is allowed. For more

information on public and private IP addresses, contact your

service provider.

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Ericsson W25 Guía de usuario Pagina 44