ATL Telecom AM30 - Manual (Page 155)

ATL Telecom User Guide
AM30
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5
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Modifying Port Settings
Overview of IP port numbers
The header information in an IP data packet specifies a destination port number. Routers
use the port number along with the specified IP addresses to forward the packet to its
intended recipient.
For example, all IP data packets that the ADSL/Ethernet router receives from the Internet
specify the same IP address (your public IP address) as the destination. However, depending
on the port number contained in a data packets, the ADSL/Ethernet router may pass the
packet on to its embedded Web or Telnet servers, or to another computer on the network.
The Internet community has developed a list of common server types such as HTTP, Telnet,
e-mail, and many others, and assigned a unique port number to each. These are not
mandatory, but are useful in promoting communication between separately administered
LANs.
Modifying the ADSL/Ethernet router’s port numbers
In some cases, you may want to assign non-standard port numbers to the HTTP and Telnet
servers that are embedded on the . The ROUTER following scenario is one example where
changing the HTTP port number may be necessary:
You have an externally visible Web server on your
LAN, with a NAT rule (RDR flavor) that redirects
incoming HTTP packets to that Web server. When
incoming packets contain a destination IP address of
your public IP address (which is assigned to the
ADSL/Ethernet router’s WAN port) and the standard
Web server port number of 80, the NAT rule
recognizes the port number and redirects the packets
to your Web server’s local IP address.
Assume in this scenario that you also want to enable
external access to the RGA-100 Configuration
Manager, so that your ISP can log in and manager
your system, for example. Accessing Configuration
Manager requires accessing the ROUTER’s own Web
server (also called its HTTP server). In this case, you
would want to use the Port Settings feature to assign
a non-standard port number to the ROUTER’s HTTP
server. Without a non-standard port number, the
NAT rule would redirect your ISP’s log in attempt to
your LAN HTTP server rather than to the HTTP server
on the ROUTER
Thereafter, when your ISP wants to log on to your
Configuration Manager, they would type your IP
address in their browser, followed by a colon and the
non-standard port number, as shown in this example:
http://10.0.1.16:61000
Your ISP may also have special circumstances that require changing the port numbers; contact
them before making any changes here.