F-6 User’s Reference GuideImportant notesEven with the advantages of NAT, there are several things you should note carefully: There is no formally agreed upon method among router vendors to handle an all-zeros IPCP request. Themajority of router vendors use the all-zeros IPCP request to determine when a dial-in host wants to beassigned an IP address. Some vendors however attempt to negotiate and establish routing with anall-zeros IP address. The Netopia R3100 will not allow routing to be established with an all-zeros IPaddress and the call will be dropped with an error logged in the Device Event History. When using NAT it is most likely that the Netopia R3100 will be receiving an IP address from a “pool” ofdynamic IP addresses at the ISP. This means that the Netopia R3100's IP presence on the Internet willchange with each connection. This can potentially cause problems with devices on the Internet attemptingto access services like WWW and FTP servers or AURP partners on the Netopia R3100’s local LANinterface. In this case, if a dynamic IP address is assigned to the WAN interface of the Netopia R3100each time, the administrator of the Netopia R3100 will have to notify clients wishing to access services onthe Netopia R3100’s LAN interface of the new IP address after each connection. With NAT enabled, there cannot be two or more of the same types of service accessible from the Interneton the LAN interface of the Netopia R3100. For example, there cannot be multiple FTP servers (Port 23) onthe Netopia R3100's LAN interface that can be accessible by workstations on the Internet. This is due tothe fact that within the Netopia R3100 and IP there is no way to distinguish between multiple servers usingthe same port, in this case port 23. Fictional IP addresses may be assigned on the Netopia R3100’s LAN interface. It is strongly recommendedthat for the Netopia R3100’s LAN interface, an IP address from the Class C address range of 192.168.X.Xbe used. This is because this range is defined by the IANA as an address space that will never be routedthrough the Internet and is to be used by private Intranets not attached to the Internet.If the address range of 192.168.X.X is not used and another range of addresses such as 100.1.1.X isused instead, this address space can potentially overlap an address space that is owned by a userattached to the Internet. Thus if a user on the Netopia R3100’s LAN interface has an IP address of100.1.1.2 while the Netopia R3100’s LAN interface is 100.1.1.2 and the local host wishes to access ahost on the Internet with the address of 100.1.1.8, the Netopia R3100 has no way of knowing that the200.1.1.8 address is actually on the Internet and not on its local LAN interface, as the local LAN interfaceis assigned the IP address range of 200.1.1.1 to 200.1.1.14.ConfigurationNetwork Address Translation is enabled by default with the SmartStart configuration utility. You can toggleEnable Address Translation to NO or YES in the Connection Profile screen in System Configuration under the IPProfile Parameters section. NAT is enabled on a per-profile basis, so it is possible to have any combination ofNAT and non-NAT profiles. An example of enabling NAT is as follows:
