User Manual

this computer obtains its address Automatically using DHCP, then you may want to make a static reservation

on the Basic → Network Settings page so that the IP address of the DMZ computer does not change.

Non-UDP/TCP/ICMP LAN Sessions

When a LAN application that uses a protocol other than UDP, TCP, or ICMP initiates a session to the Internet,

the router's NAT can track such a session, even though it does not recognize the protocol. This feature is

useful because it enables certain applications (most importantly a single VPN connection to a remote host)

without the need for an ALG.

Note that this feature does not apply to the DMZ host (if one is enabled). The DMZ host always handles these

kinds of sessions.

Enable

Enabling this option (the default setting) enables single VPN connections to a remote host. (But, for multiple

VPN connections, the appropriate VPN ALG must be used.) Disabling this option, however, only disables VPN

if the appropriate VPN ALG is also disabled.

Application Level Gateway (ALG) Configuration

Here you can enable or disable ALGs. Some protocols and applications require special handling of the

IP payload to make them work with network address translation (NAT). Each ALG provides special

handling for a specific protocol or application. A number of ALGs for common applications are enabled

by default.

PPTP

Allows multiple machines on the LAN to connect to their corporate networks using PPTP protocol. When the

PPTP ALG is enabled, LAN computers can establish PPTP VPN connections either with the same or with

different VPN servers. When the PPTP ALG is disabled, the router allows VPN operation in a restricted way --

LAN computers are typically able to establish VPN tunnels to different VPN Internet servers but not to the

same server. The advantage of disabling the PPTP ALG is to increase VPN performance. Enabling the PPTP

ALG also allows incoming VPN connections to a LAN side VPN server (refer to Advanced → Virtual Server).

IPSec (VPN)

Allows multiple VPN clients to connect to their corporate networks using IPSec. Some VPN clients support

traversal of IPSec through NAT. This option may interfere with the operation of such VPN clients. If you are

having trouble connecting with your corporate network, try disabling this option.

Check with the system adminstrator of your corporate network whether your VPN client supports NAT

traversal.

Note that L2TP VPN connections typically use IPSec to secure the connection. To achieve multiple VPN

pass-through in this case, the IPSec ALG must be enabled.

RTSP

Allows applications that use Real Time Streaming Protocol to receive streaming media from the internet.

QuickTime and Real Player are some of the common applications using this protocol.

Windows/MSN Messenger

Supports use on LAN computers of Microsoft Windows Messenger (the Internet messaging client that ships

with Microsoft Windows) and MSN Messenger. The SIP ALG must also be enabled when the Windows

Messenger ALG is enabled.

FTP

Allows FTP clients and servers to transfer data across NAT. Refer to the Advanced → Virtual Server page if

you want to host an FTP server.

H.323 (Netmeeting)

Allows H.323 (specifically Microsoft Netmeeting) clients to communicate across NAT. Note that if you want

your buddies to call you, you should also set up a virtual server for NetMeeting. Refer to the

Advanced → Virtual Server page for information on how to set up a virtual server.