ZyXEL Communications NBG7815, User Manual, Page: 99 / 186

Chapter 9 WAN
NBG7815 User’s Guide
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9.7 Port Trigger
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, 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.
Port trigger addresses this problem. Port trigger allows computers on the LAN to dynamically take turns
using the service. The NBG7815 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 (a "trigger" port). When the NBG7815's
WAN port receives a response with a specific port number and protocol ("open" port), the NBG7815
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.
Note: TCP port 7547 is reserved for system use.
Note: The maximum number of port triggers for a single rule or all rules is 999.
Note: The maximum number of open ports for a single rule or all rules is 999.
Figure 50 Port Trigger Process: Example
1
Jane ( A ) requests a file from the Real Audio server ( B , port 7070).
IPSEC Select Enable to allow VPN clients to make outbound IPSec connections. It is required in
order to connect to a IPSec VPN account. If IPSEC is disabled, then when a client sends a
request to a VPN server, the server will reply to the NBG7815 and the NBG7815 will drop the
request. When
IPSEC is enabled, the NBG7815 will forward the reply from the VPN server to
the client that initiated the request, and the connection will establish successfully.
APPLY Click APPLY to save your changes back to the NBG7815.
CANCEL Click CANCEL to begin configuring this screen afresh.
Table 31 Settings > Internet > Passthrough (continued)
LABEL DESCRIPTION