TRENDnet TDM-C400 User's Guide - Page 181

Modifying Port Settings, Overview of IP port numbers

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18 Modifying Port Settings This chapter describes how to modify the Port ID numbers associated with the Ethernet Modem Router's Web, FTP, and Telnet servers. 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 IP addresses to forward the packet to its intended recipient. For example, all IP data packets that the ADSL2+ Ethernet Modem 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 ADSL2+ Ethernet Modem 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 has defined port numbers that can be assigned each. This is not a mandatory scheme, but is useful in promoting communication between separately administered LANs. Modifying the Ethernet Modem 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 Ethernet Modem Router . The following scenario is one example in which 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 ADSL2+ Ethernet Modem Router's WAN interface) 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 Ethernet Modem Router 's Web Configuration, so that your ISP can log in and manager your system, for example. Accessing Web Configuration requires accessing the Ethernet Modem 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 Ethernet Modem Router 's HTTP server. Without a non-standard port number, the NAT rule would redirect your ISP's log in 181

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181
18
Modifying Port Settings
This chapter describes how to modify the Port ID numbers
associated with the Ethernet Modem Router’s Web, FTP, and
Telnet servers.
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 IP
addresses to forward the packet to its intended recipient.
For example, all IP data packets that the ADSL2+ Ethernet Modem
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 ADSL2+ Ethernet
Modem 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 has
defined port numbers that can be assigned each. This is not a
mandatory scheme, but is useful in promoting communication
between separately administered LANs.
Modifying the Ethernet Modem 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 Ethernet
Modem Router . The following scenario is one example in which
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 ADSL2+ Ethernet
Modem Router’s WAN interface) 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 Ethernet Modem Router ’s Web
Configuration, so that your ISP can log in and manager
your system, for example. Accessing Web Configuration
requires accessing the Ethernet Modem 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 Ethernet Modem
Router ’s HTTP server. Without a non-standard port
number, the NAT rule would redirect your ISP’s log in