ZyXEL Communications NBG-415N, User Manual

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ZyXEL NBG-415N User’s Guide
Chapter 7 Advanced 76
7.3 Applications
You can enable Application Layer Gateway (ALG) to allow certain NAT un-friendly
applications (such as SIP) to operate properly through the ZyXEL Device. Alternatively, you
can configure port triggering to allow computers on the LAN to dynamically take turns using
the service
7.3.1 Port Triggering
Some services use a dedicated range of ports on the client side and a dedicated range of ports
on the server side. With regular port forwarding (or virtual server setup) you set a forwarding
port in NAT to forward a service (coming in from the server on the WAN) to the IP address of
a computer on the client side (LAN). The problem is that port forwarding only forwards a
service to a single LAN IP address. In order to use the same service on a different LAN
computer, you have to manually replace the LAN computer's IP address in the forwarding port
with another LAN computer's IP address.
Trigger port forwarding solves this problem by allowing computers on the LAN to
dynamically take turns using the service. The ZyXEL Device records the IP address of a LAN
computer that sends traffic to the WAN to request a service with a specific port number and
protocol ("trigger" port and protocol). When the ZyXEL Device's WAN port receives a
response with a specific port number and protocol ("input" port and protocol), the ZyXEL
Device forwards the traffic to the LAN IP address of the computer that sent the request. After
that computer’s connection for that service closes, another computer on the LAN can use the
service in the same manner. This way you do not need to configure a new IP address each time
you want a different LAN computer to use the application.
Enable Select this check box to enable this virtual server setting. Clear this check box to
disallow forwarding of these ports to an inside server without having to delete the
entry.
Name This field displays the descriptive name for this setting.
IP Address This field displays the IP address of the inside server.
Protocol This field displays the protocol type.
Private Port This field displays the port number to which you want the ZyXEL Device to translate
the public port.
Public Port This field displays the incoming port number.
Inbound Filter This field displays the name of the filter on the incoming traffic.
Schedule This field displays the name of the schedule to use.
Table 28 Advanced: Virtual Server (continued)
LABEL DESCRIPTION