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Chapter 7 Network Setting
Trigger Ports
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,
Trigger port forwarding solves this problem by allowing computers on the LAN to
dynamically take turns using the service. The MAX208M2W Series 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 MAX208M2W
Series's WAN port receives a response with a specific port number and protocol
("incoming" port), the MAX208M2W Series 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.
ALG
Some applications, such as SIP, cannot operate through NAT (are NAT un-friendly)
because they embed IP addresses and port numbers in their packets' data
payload. Some NAT routers may include a SIP Application Layer Gateway (ALG).
An Application Layer Gateway (ALG) manages a specific protocol (such as SIP,
H.323 or FTP) at the application layer.
A SIP ALG allows SIP calls to pass through NAT by examining and translating IP
addresses embedded in the data stream.
UPnP
Universal Plug and Play (UPnP) is a distributed, open networking standard that
uses TCP/IP for simple peer-to-peer network connectivity between devices. A
UPnP device can dynamically join a network, obtain an IP address, convey its
capabilities and learn about other devices on the network. In turn, a device can
leave a network smoothly and automatically when it is no longer in use.
How do I know if I'm using UPnP?
UPnP hardware is identified as an icon in the Network Connections folder
(Windows XP). Each UPnP compatible device installed on your network will appear
as a separate icon. Selecting the icon of a UPnP device will allow you to access the
information and properties of that device.
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MAX208M2W Series User's Guide
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