Dynamic addressing involves the assignment to each caller of the IP address that is defined in /etc/ppp/options.ttyname. Dynamic addressing occurs on a per-serial port basis. When a call arrives over a serial line, the caller receives the IP address in the /etc/ppp/options.ttyname file for the call's serial interface.
For example, suppose a dial-in server has four serial interfaces that provide dial-up service to incoming calls:
For serial port term/a, create the file /etc/ppp/options.term.a with the following entry:
For serial port term/b, create the file /etc/ppp/options.term.b with the following entry:
For serial port term/c, create the file /etc/ppp/options.term.c with the following entry:
For serial port term/d, create the file /etc/ppp/options.term.d with the following entry:
With the previous addressing scheme, an incoming call on serial interface /dev/term/c is given the IP address 10.1.1.3 for the duration of the call. After the first caller hangs up, a later call that comes in over serial interface /dev/term/c is also given the IP address 10.1.1.3.
The advantages of dynamic addressing include the following:
You can track PPP network usage down to the serial port.
You can assign a minimum number of IP addresses for PPP use.
You can administer IP filtering in a more simplified fashion.