Requires Optional LAN/X.25 Software

NAME

ppl − point-to-point serial networking

SYNOPSIS

ppl [-o|-i] [-t tty] [-v] [-r rtprio] [remote_host]

DESCRIPTION

ppl extends the Internet Protocol (IP) network over serial lines.  It permits the use of hardwired, dial-out, or dial-in serial (tty) lines.  ppl establishes a connection over the serial line, then runs an encapsulation protocol to transfer packets between the IP network and the serial line.  Once started, ppl can only be stopped by loss of the serial line (i.e. carrier failure indication from a modem), or by sending it a SIGTERM signal. 

Currently only the SLIP (Serial Line Internet Protcol) and ASLIP (Abbreviated SLIP) encapsulation protocols are available. 

ppl can be configured in a number of ways, and behaves according to how it is configured and the command line options used.  Configuration is controlled by configuration files: ppl.remotes , ppl.ipool , and ppl.users .  ppl can be configured to share UUCP serial lines. 

Options

-i Run the encapsulation protocol on the terminal device from which the program is invoked.  This is the default if neither -o nor -i is specified. 

-o The terminal on which the data pump is started is determined from configuration files, UUCP, or the -t option. 

-t devicename Specifies the devicename on which the encapsulation protocol is started, only if a device name is not specified in configuration file ppl.remotes for the remote host.  This option only applies when used with the -o option. 

-v Be verbose. This option is only available to the super-user.  Verbose debugging information is displayed on the terminal and placed in the log.  Secure information is included. 

-r rtprio Set real-time priority during data pump operation.  rtprio can be a decimal number between 0 and 127.  By default, ppl runs at a real-time priority of 110. 

remote_host specifies the remote host to communicate with.  Either a name or an Internet address (in dot format) can be supplied.  This must be the last argument on the command line.  If none is supplied (with the -i option), the users login name is used to find one in the ppl.users file. 

Dedicated Connections

Dedicated connections are lines that are dedicated to ppl. There is no getty/login running on the local or remote end of the serial line. Such a line can be either hard-wired, dial-out, or dial-in.

Alternatively, ppl can run on lines that are used for other purposes; specifically, a getty/login on incoming lines, or shared with UUCP on outgoing lines. 

Dial-Out Connections

To dial out from an HP-UX system, use a command resembling:

ppl -o remote_host

to establish a connection to a remote host.  Any progress or error messages are directed to the users standard error.  ppl accesses the ppl.remotes file to obtain information needed to establish the connection.  If necessary, it also uses UUCP files to select a line, acquire the phone number, and control the modem.  Note that ppl uses various files created and maintained by the UUCP system, but it does not use the UUCP facility to handle inter-system communication. 

The UUCP line is selected as follows:

1.  If the entry in configuration file ppl.remotes does not contain a tty device name, ppl looks in the UUCP Systems file for a tty device (and speed), based on the ppl.remotes entry UUCP system name or remote host name. 

2.  ppl then searches for the tty device name and speed in the UUCP Devices file.  This information is used for modem dialing instructions. 

After a successful connection is made, ppl makes itself into a “daemon” by detaching itself from the users tty group.  The user gets back a shell prompt, and the ppl program runs in the background.  The user can then perform network commands to the remote host. 

Dial-In Connections

To make a dial-in connection to an HP-UX system, dial in on a serial line to the HP-UX system, and log in as usual.  Once logged in, the line can be converted from log-in to network use by running ppl.  The ppl program uses the login name to search ppl.users for a remote hostname.  The remote hostname is used to access the ppl.remotes file to obtain all of the configuration information needed to start the protocol.  ppl then starts the desired protocol.  Once the protocol starts, the users’ local machine can begin packet transfers with ppl.  ppl never (voluntarily) exits, and therefore never returns a prompt. 

Only one invocation of ppl is allowed to each remote host Internet address. 

A unique local Internet address must be associated with each invocation of ppl.  This can be specified in the ppl.remotes file, or it can be picked at run time from a pool of Internet addresses given in ppl.ipool. 

Log Files

ppl keeps a log of its activities in /usr/spool/ppl/log. 

Another log can optionally be kept for creating bills or keeping track of serial line usage.  If the file /usr/spool/ppl/bill exists, ppl adds an entry to this file each time it gracefully exits.  The contents of the billing file are in human readable ASCII form.  The file is also program readable, suitable for export to various databases.  It contains the following fields, separated by ;: bill end time, bill start time, Local inetaddr, Remote inetaddr, login user name, tty name, and protocol.

The current status of all invocations of ppl are kept updated in file /usr/spool/ppl/ptmp if the file exists. 

Lock Files

ppl creates two lock files for each invocation of the program.  These lock files serve three purposes:

• They lock access to the Internet network address by encoding the Internet address (in hex) as part of the file name. 

• The files contain various details about the connection. 

• The files can be executed (by owner or root) as a shell script.  When executed, they send a signal to ppl, causing it to exit gracefully.

Whenever ppl exits gracefully, it removes these lock files and releases resources. 

If ppl uses a UUCP line, it observes and creates UUCP lock file protocol. 

Gateway Packets

ASLIP is an abbreviated header enhancement to SLIP.  It provides throughput economy in non-gateway applications.  One end of an ASLIP line must act as a “client”; the other end as a “server”.  Typically the client is a personal workstation; the server a larger machine. 

The client sends non-gateway packets using ASLIP and gateway packets using SLIP.  The server adapts its operation to the behavior of the client.  ASLIP operation must be specified in the ppl.remotes file. 

FILES

/usr/lib/ppl/ppl.remotes all options for each remote connection

/usr/lib/ppl/ppl.ipool pool of local internet addresses that can be used

/usr/lib/ppl/ppl.users translates users login name to a remote host

/usr/spool/ppl/PPL.xxxx termination command file and lock file for local Internet address

/usr/spool/ppl/ppl.xxxx termination command file and lock file for remote Internet address

/usr/spool/ppl/log audit trail and log file

/usr/spool/ppl/bill billing file (optional)

/usr/spool/ppl/ptmp status file (optional)

AUTHOR

ppl was developed by HP. 

WARNINGS

The log and bill files grow without bound. 

SEE ALSO

pplstat(1), ppl.remotes(4), ppl.ipool(4), ppl.users(4), ppl.ptmp(4),
Using Serial Line IP Protocols, UUCP tutorial in Remote Access Users Guide.

Hewlett-Packard Company  —  HP-UX Release 9.0: August 1992