Inbound Rules To Permit External Host Communications - NETGEAR DM111PSPv2 User Manual

Inbound Rules to Permit External Host Communications

In both of the preceding examples, your computer initiates an application session with a
server computer on the Internet. However, you might need to allow a client computer on the
Internet to initiate a connection to a server computer on your network. Normally, your router
ignores any inbound traffic that is not a response to your own outbound traffic. You can
configure exceptions to this default rule by using the inbound rules feature.
A typical application of inbound rules can be shown by reversing the client-server relationship
from the previous web server example. In this case, a remote computer's browser needs to
access a web server running on a computer in your local network. By using inbound rules,
you can tell the router, "When you receive incoming traffic on port 80 (the standard port
number for a web server process), forward it to the local computer at 192.168.1.123." The
following sequence shows the effects of the inbound rule you have defined:
1. The user of a remote computer opens a browser and requests a web page from
www.example.com, which resolves to the public IP address of your router. The remote
computer composes a web page request message with the following destination
information:
Destination address. The IP address of www.example.com, which is the address of your
router.
Destination port number. 80, which is the standard port number for a web server
process.
The remote computer sends this request message through the Internet to your router.
2. Your router receives the request message and looks in its rules table for any rules covering
the disposition of incoming port 80 traffic. Your inbound rule specifies that incoming port 80
traffic should be forwarded to local IP address 192.168.1.123. Therefore, your router
modifies the destination information in the request message:
The destination address is replaced with 192.168.1.123.
Your router then sends this request message to your local network.
3. Your web server at 192.168.1.123 receives the request and composes a return message
with the requested web page data. Your web server then sends this reply message to your
router.
4. Your router performs Network Address Translation (NAT) on the source IP address, and
sends this request message through the Internet to the remote computer, which displays the
web page from www.example.com.
To configure inbound rules, you need to know which inbound ports the application needs. You
usually can determine this information by contacting the publisher of the application or the
relevant user groups or newsgroups.
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