For the dial-in server, you must use the IP address of the server's primary network interface (for example le0 or smc0) as the address of the dynamic link.
For a dynamic link, you don't need to assign an IP address to each remote host (as you would for a static link), but you do need to assign a remote IP address to each point-to-point IP interface on the server. The number of IP interfaces you can use is equal to the number of modems your server is connected to. For example, if you have three modems, you need three point-to-point IP interfaces and three IP addresses
You must include a dummy IP address for the ifconfig command to work properly on the client. This address acts as a placeholder for the local IP address assigned to the client IP interface when PPP is started.
There are no restrictions on the remote IP addresses that can be assigned to the IP interfaces, but, for clarity, it is probably best to include only IP addresses belonging to the same subnet.