User's Manual

Chapter20 NEOBIT 1014VA ADSL Router User’s Guide
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 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 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 Routers’ 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 NEOBIT
1014VA. The following scenario is one example of why 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 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 [NEOBIT 1014VA’s] Configuration
Manager, so that your ISP can log in and manager your
system, for example. Accessing Configuration Manager
requires accessing the [NEOBIT 1014VA’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 NEOBIT 1014VA’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 NEOBIT
1014VA.
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 HTTP or Telnet port numbers; contact them before