Hypertec ISDN 10T Router manual Nat

Concepts and Principles of Operation

packets are to be filtered or forwarded. If no access list is specified, all valid packets will be forwarded. You can specify in the IP access list the following criteria: source IP address, destination IP address, source port number, destination port number, and the protocol which when matched will be forwarded or filtered.

NAT

The ISP generally offers two type of accounts to SOHO users. The Single User account, and the LAN Access (Multiple Users) account. The Single User account is often referred as Terminal Adapter or Modem account where single user Internet access is assumed. The LAN Access account cost more than the Single User account because multiple IP addresses are assigned. Network Translation (NAT) is designed to allow multiple users on the LAN to access Internet simultaneously using the Single User account. In addition to cost saving, NAT is also useful in areas in which security or convenience are a concern. It is convenient in the sense that, the users don’t have to change the private legacy IP addressed already in use.

In order for the outside world to access the TCP/IP servers on the LAN, the Hypertec Router allows a list of internal IP addresses to be associated with FTP, Telnet, HTTP, and Email servers. Traffic destined for the list servers are forwarded to the specified IP addresses. The inbound traffic distribution works only for static IP address arrangement where you can register an IP address against the domain names. You will not have an IP address to register or publish when access to the Internet is via a “single-user” account.

There are some limitation on the NAT application :

1.If the ISDN connection drops (e.g., because of an idle time-out), it is most likely that upon reconnection you will get a different IP address assigned. For example, if you are using a web browser and the connection drops because you go idle, if you then click on a link, you might get an error message because you now have a different IP address.

2.Certain applications, like some UDP-based Internet games and chat client programs, will work unreliably or not at all when using NAT because they report their private IP address to the server

instead of the "correct" dynamically assigned address. The remote application while sending UDP packets toward the private IP address will not be able to deliver.

3.

NAT is available for Internet connections only. The Intranet connection is not affected by the Internet NAT setting.

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