You can configure the characteristics of communications on the serial line in the /etc/ppp/options.ttyname file. /etc/ppp/options.ttyname is a privileged file that is read by pppd after parsing any existing /etc/ppp/options and existing $HOME/.ppprc files. Otherwise, pppd reads /etc/ppp/options.ttyname after parsing /etc/ppp/options.
ttyname is used for both dial-up and leased-line links. ttyname represents a particular serial port on a machine, such as cua/a or cua/b, where a modem or ISDN TA might be attached.
When naming the /etc/ppp/options.ttyname file, replace the slash (/) in the device name with a dot (.). For example, the options file for device cua/b should be named /etc/ppp/options.cua.b.
For a dial-up link, you might choose to create individual /etc/ppp/options.ttyname files for every serial port on a dial-in server with a modem attached. Typical options include the following:
IP address required by the dial-in server
Set this option if you require incoming callers on serial port ttyname to use a particular IP address. Your address space might have a limited number of IP addresses that are available for PPP in comparison to the number of potential callers. In this situation, consider assigning an IP address to each serial interface that is used for PPP on the dial-in server. This assignment implements dynamic addressing for PPP.
asyncmap map-value
The asyncmap option maps control characters that cannot be received over the serial line by the particular modem or ISDN TA. When the xonxoff option is used, pppd automatically sets an asyncmap of 0xa0000.
map-value states, in hexadecimal format, the control characters that are problematic.
init "chat -U -f /etc/ppp/mychat"
The init option tells the modem to initialize communications over the serial line by using the information in the chat –U command. The modem uses the chat string in the file /etc/ppp/mychat.
Security parameters that are listed in the pppd(1m) man page
For a dial-out system, you can create an /etc/ppp/options.ttyname file for the serial port that is connected to the modem, or choose not to use /etc/ppp/options.ttyname.
The /etc/ppp/options.ttya.tmpl file contains helpful comments about the /etc/ppp/options.tty-name file. The template contains three common options for the /etc/ppp/options.tty-name file.
38400 asyncmap 0xa0000 :192.168.1.1
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To use /etc/ppp/options.ttya.tmpl at your site, rename /etc/ppp/options.tmpl to /etc/ppp/options.ttya-name. Replace ttya-name with the name of the serial port with the modem. Then modify the file contents as needed by your site.
To find examples of the /etc/ppp/options.ttyname files, refer to the following:
For a dial-out machine, see How to Define Communications Over the Serial Line.
For a dial-in server, see How to Define Communications Over the Serial Line (Dial-in Server).