DIP(8)

NAME
dip - handle dialup IP connections

SYNOPSIS
dip [-v] [-m mtu] [-p proto] scriptfile
dip -t [-v]
dip -i [-a] [-v]
diplogin [username]
diplogini
dip [-v] -k [-l tty_line]

DESCRIPTION
dip handles the connections needed for dialup IP links, like SLIP or PPP. It can handle both incoming and outgoing connections, using password security for incoming connections. The outgoing connections use the system's dial(3) library if available.

The first form interprets scriptfile to dial out and open an IP connection (see DIALOUT MODE below).

The -t option runs dip interactively (see COMMAND MODE below). This is most useful while gathering data to set up a chat script.

dip -i handles incoming connections (see DIALIN MODE below). diplogin is equivalent to dip -i, and diplogini is equivalent to dip -i -a. These are mainly for use with versions of login(1) that do not pass command line parameters to the shell program.

dip -k kills an existing dip process, closing the connection.

OPTIONS

-a  Prompt for user name and password.

-i  Act as a dialin server (see DIALIN MODE below).

-k  Kill the dip process that runs (has locked) the specified tty device (see -l option), or else the most recent invocation of dip. Note that dip takes care not to kill a process started by somebody else (unless it's root who demands the operation :-).

-l tty_line
    Indicate the line to be killed. (Requires -k option.)

-m mtu
    Set the Maximum Transfer Unit (MTU) (default 296).

-p proto
    Set the line protocol. proto must be one of: SLIP, CSLIP, SLIP6, CLSIP6, PPP, or TERM.

-t  Run in test mode (see COMMAND MODE below).

-v  Set verbose mode. This enables various debug printouts, including an echo of each line of the chat script.

COMMAND MODE
The first possible use of dip is as an interactive program to set up an outgoing IP connection. This can be done by invoking dip with the -t option, which means enter TEST mode and, more precisely, dumps you in the COMMAND-MODE of the dip program. You are reminded of this by the DIP> prompt, or, if you also specified the -v debugging flag, the DIP [NNNN]> prompt. The latter prompt also displays the current value of the global $errlvl variable, which is used mostly when dip runs in script mode. For the interactive mode, it can be used to determine if the result of the previous command was OK or not.

The following is a sample taken from a live session:

$dip -t
DIP: Dialup IP Protocol Driver version 3.3.7n-uri (7 Mar 95)
Written by Fred N. van Kempen, MicroWalt Corporation.
DIP> _

The possible commands are listed below (see COMMANDS). Note particularly the help command. Each command displays a usage message if it is invoked incorrectly. Just experiment a little to get the feel of it, and have a look at the sample script file, which also uses this command language (see EXAMPLES).

DIALOUT MODE
The second way of using dip is to initiate outgoing connections. To make life easier for the people who have to manage links of this type, dip uses a chat script to set up a link to a remote system. This gives the user an enormous amount of flexibility when making the connection, which otherwise could require many command-line options. The path name of the script to be run is then given as the single argument to dip. If scriptfile has no file extension, dip will automatically add the extension ".dip". This is just a way to group scripts together in a single directory.

DIALIN MODE
The third possible way of using dip is as a login shell for incoming IP connections, as in dialup SLIP and PPP connections. To make integration into the existing UNIX system as easy as possible, dip can be installed by simply naming it as the login shell in /etc/passwd. A sample entry looks like:

suunet:ij/SMxiTlGVCo:1004:10:UUNET:/tmp:/usr/sbin/diplogin

When user suunet logs in, the login(1) program sets the home directory to /tmp and executes the diplogin program. diplogin should be a symbolic link to dip, which means that dip must run in input mode. dip then tries to locate the name of the logged in user (i.e. the name corresponding to its current user id, as returned by the getuid(2) system call) in its database file. An optional single argument to the dip program in this mode can be the username that must be used in this lookup, regardless the current user id.

dip now scans /etc/diphosts for an entry for the given user name. This file contains lines of text (much like the standard password file). Any line starting with # is a comment. Otherwise, each line has seven colon-separated items, in the format
user : password : remote host : local host : netmask :
      comments : protocol,MTU
The first field of a line is the user name, which we must match.

The second field can contain an encrypted password. If this field is non-null, dip displays the prompt "External security password:", and the reply must match the password in this field. If this field is "s/key" (check the value of SKEY_TOKEN in dip.h) and dip was compiled with S/Key enabled, then S/Key authentication will take place (see README.SKEY in the dip source directory).

The third field contains the name (or raw IP address) of the remote host. If a host name is given, the usual address resolving process is started, using either a name server or a local hosts file.

The fourth field contains the name (or raw IP address) of the local host. If a host name is given, it's resolved, just like the remote host name in the third field.

The fifth field contains the netmask in decimal dotted notation (like 255.255.255.0). If empty, 255.255.255.0 is used by default.

The sixth field may contain any text; it is not used by dip.

Finally, the seventh field of a line contains a mixture of comma-separated flags. Possible flags are:

SLIP to indicate we must use the SLIP protocol.
CSLIP to indicate Compressed SLIP protocol.
AUTO to autodetect whether the client uses SLIP or CSLIP
SLIP6 to indicate we must use the SLIP6 protocol.
CSLIP6 to indicate Compressed SLIP6 protocol.
PPP to indicate we must use the PPP protocol.
number which gives the MTU parameter of this connection.

Please note: my experience shows smaller blocks (i.e. smaller MTU) work better. You *can* define MTU 1500, but it won't vouch for your sanity.

After finding the correct line, dip puts the terminal line into RAW mode, and asks the system networking layer to allocate a channel of the desired protocol. Finally, if the channel is activated, it adds an entry to the system's routing table to make the connection work.

dip now goes into an endless loop of sleeping, which continues until the connection is physically aborted (i.e. the line is dropped). At that time, dip removes the entry it made in the system's routing table, and releases the protocol channel for re-use. It then exits, making room for another session.

COMMANDS
The following may appear in a chat script. Most can also be used in command mode:

label:
    Define a label.

beep [times]
    Beep on user's terminal [this many times].

bootp [howmany [howlong]]
    Use BOOTP protocol to fetch local and remote IP addresses.

break
    Send a BREAK.

chatkey keyword [code]
    Add to dip's collection of modem response words. For example,
    chatkey CONNECT 1
    would duplicate one of the existing entries.

config [interface|routing] [pre|up|down|post] {arguments...}
    Store interface configuration parameters. (This may be disabled by the administrator.)

databits 7|8
    Set the number of data bits.

dec $variable [decrement-value|$variable]
    Decrement a variable. The default decrement-value is 1.

default
    Tells DIP to set up the default route to the remote host it made a connection to. If this command isn't present in the command file, the default route won't be set/changed.

dial phonenumber [timeout]
    Sends the string in the init variable to initialize the modem and then dials the indicated number. The default timeout is 60 sec. dip parses the string returned by the modem, and sets $errlvl accordingly. The standard codes are as follows:
    	0	OK
    	1	CONNECT
    	2	ERROR
    	3	BUSY
    	4	NO CARRIER
    	5	NO DIALTONE
    You can change or add to these with the chatkey command.

echo on|off
    Enables or disables the display of modem commands.

exit [exit-status]
    Exit script leaving established [C]SLIP connection intact and dip running.

flush
    Flush input on the terminal.

get $variable [value | ask | remote [timeout_value | $variable]]
    Get or ask for the value of a variable. If the second parameter is ask, a prompt is printed and the value is read from standard input. If it is remote, it is read from the remote machine. Otherwise, the second parameter is a constant or another variable which supplies the value.

goto label
    Transfer control to the indicated label in the chat script.

help
    Print list of commands, similar to this:

    DIP> help
    DIP knows about the following commands:
       beep     bootp    break    chatkey  config   databits
       dec      default  dial     echo     flush    get
       goto     help     if       inc      init     mode
       modem    netmask  onexit   parity   password proxyarp
       print    port     quit     reset    securid  securidfixed
       send     shell    sleep    speed    stopbits term
       timeout  wait
    DIP> _

if expr goto label
    Test some result code. The expr must have the form
    $variable op constant
    where op is one of: == != < > <= >=.

inc $variable [increment-value|$variable]
    Increment a variable. The default increment-value is 1.

init init-string
    Set the initialization string (sent to the modem before dialing with the dial command) to the indicated string (default is ATE0 Q0 V1 X4). Please use it!

mode SLIP|CSLIP|SLIP6|CSLIP6|PPP|TERM
    Set the line protocol (default SLIP).

modem modem-name
    Set the type of modem. (The default, and at present the only legal value, is HAYES).

netmask xxx.xxx.xxx.xxx
    Indicate the netmask we will want to use.

onexit .......
    Execute a command upon dip's exit. This works exactly like the shell command, but it is only executed when dip finishes (as it's name indicates ... ;). The onexit command which is executed is the one you entered last, thus, previous onexit commands are deleted by the new ones (confused? me too :).

parity E|O|N
    Set the type of parity.

password
    Prompt for a password and send it.

proxyarp
    Request Proxy ARP to be set.

print $variable
    Print the contents of some variable.

psend command [arguments]
    Send the output of command to the serial driver, optionally passing arguments to command. The UID is reset to the real UID before running command.

port tty_name
    Set the name of the terminal port to use. (The path /dev/ is assumed.)

quit
    Exit with nonzero exit status.

reset
    Reset the modem. (Sends "+++" then "ATZ".) Does not work properly on several modems, so beware! I do not use it.

securidfixed fixedpart
    Store the fixed part of the SecureID password.

securid
    Prompt for the variable part of the password generated by the ACE System SecureID card. The fixed part of the password must already have been stored using a secureidf command. The two parts are concatenated and sent to the remote terminal server.

send text-string
    Send a string to the serial driver.

shell command [parameters]
    Executes command through the default shell (obtained from the SHELL variable) with parameters as the command-line arguments. Dip variable substitution is performed before executing the command. If you don't want a parameter beginning with a $ to be interpreted as a dip variable, precede it with a \.

skey [timeout | $variable]
    This tells dip to look for an S/Key challenge from the remote terminal server. dip then prompts the user for the secret password, generates the response, and sends it to the remote host. The optional parameter timeout sets how long dip is to wait to see the challenge. $errlvl is set to 1 if the skey command times out. If skey successfully sends a response, $errlvl is set to 0. Requires S/Key support to be compiled in.

sleep time-in-secs
    Wait some time.

speed bits-per-sec
    Set port speed (default 38400). Note that the actual speed associated with "38400" can be changed using setserial(8). Also, you should tell port's real speed here, as dip takes care of the set_hi and such bits by itself. Also, don't be afraid, if you told the speed "57600" and it reports back "38400" - everything's OK, the proper flags were applied and the real port speed will be what you told it to be, i.e. "57600".

stopbits 1|2
    Set the number of stop bits.

term
    Enter a terminal mode.

timeout time-in-sec
    Set timeout. This defines the period of inactivity on the line, after which DIP will force the line down and break the connection (and exit).

wait text [timeout_value | $variable]
    Wait for some string to arrive.

  SPECIAL VARIABLES

$errlvl
    Holds the result of the previous command.

$locip
    IP number of local host in dotted quad notation (for example, 128.96.41.50).

$local
    Fully qualified local host name (for example, sunsite.unc.edu).

$rmtip
    IP number of remote host in dotted quad notation.

$remote
    Fully qualified remote host name.

$mtu
    Maximum Transfer Unit (maximum number of bytes transferred at once).

$modem
    Modem type (at present the only valid value is HAYES).

$port
    The name of the terminal port to use. (The path /dev/ is assumed.)

$speed
    Transfer rate between the local host and the modem, in bits/sec.

EXAMPLES
Here is a sample /etc/diphosts:

#
# diphosts	This file describes a number of name-to-address
#		mappings for the DIP program.  It is used to determine
#		which host IP address to use for an incoming call of
#		some user.
#
# Version:	@(#)diphosts		1.20	05/31/94
#
# Author:	Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>
# Modified:     Uri Blumenthal      <uri@watson.ibm.com>
#
# name : pwd : hostname : local server: netmask: comments : protocol,mtu
#==================================================
sbonjovi::bonjovi:server1:netmask:MicroWalt "bonjovi" SLIP:SLIP,296
sroxette::roxette:server2:netmask:MicroWalt "roxette" SLIP:CSLIP,296
stephen:s/key:tuin:server3:netmask:S/Key Authenticated login:CSLIP,296
# End of diphosts.

A chat script should look something like this:

#
# sample.dip	Dialup IP connection support program.
#
# Version:	@(#)sample.dip	1.40	07/20/93
#
# Author:	Fred N. van Kempen, <waltje@uWalt.NL.Mugnet.ORG>
#
main:
  # First of all, set up our name for this connection.
  # I am called "uwalt.hacktic.nl"  (== 193.78.33.238)
  get $local uwalt.hacktic.nl
  # Next, set up the other side's name and address.
  # My dialin machine is called 'xs4all.hacktic.nl' (== 193.78.33.42)
  get $remote xs4all.hacktic.nl
  # Set netmask on sl0 to 255.255.255.0
  netmask 255.255.255.0
  # Set the desired serial port and speed.
  port cua02
  speed 38400
  # Reset the modem and terminal line.
  # This seems to cause trouble for some people!
  reset
# Note! "Standard" pre-defined "errlvl" values:
#	0 - OK
#	1 - CONNECT
#	2 - ERROR
#	3 - BUSY
#	4 - NO CARRIER
#	5 - NO DIALTONE
#
# You can change these with the chatkey command
  # Prepare for dialing.
  get $init ATQ0V1E1X4
  dial 555-1234567
  if $errlvl != 1 goto modem_trouble
  # We are connected.  Login to the system.
login:
  sleep 2
  wait ogin: 20
  if $errlvl != 0 goto login_error
  send MYLOGIN\n
  wait ord: 20
  if $errlvl != 0 goto password_error
  send MYPASSWD\n
loggedin:
  # We are now logged in.
  wait SOMETEXT 15
  if $errlvl != 0 goto prompt_error
  # Set up the SLIP operating parameters.
  get $mtu 296
  # Ensure "route add -net default xs4all.hacktic.nl" will be done
  default
  # Say hello and fire up!
done:
  print CONNECTED $locip ---> $rmtip
  mode CSLIP
  goto exit
prompt_error:
  print TIME-OUT waiting for SLIPlogin to fire up...
  goto error
login_trouble:
  print Trouble waiting for the Login: prompt...
  goto error
password_error:
  print Trouble waiting for the Password: prompt...
  goto error
modem_trouble:
  print Trouble occurred with the modem...
error:
  print CONNECT FAILED to $remote
  quit 1
exit:
  exit

This script causes dip to dial up a host, log in, and get a SLIP interface channel going (in the same manner as with incoming connections). When all is set up, it simply goes into the background and waits for a hangup (or just a lethal signal), at which it hangs up and exits.

FILES
/etc/passwd
/etc/diphosts
/etc/rc.dip (for example)

BUGS
Virtually none - what you see are features (:-).

AUTHORS
Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>,
Uri Blumenthal <uri@watson.ibm.com>,
Paul Cadach <paul@paul.east.alma-ata.su>,
Colten Edwards <edwac@sasknet.sk.ca>,
Olaf Kirch <okir@monad.sub.de>,
Pauline Middelink <middelin@calvin.iaf.nl>,
Paul Mossip <mossip@vizlab.rutgers.edu>,
Bill Reynolds,
Jim Seagrave <jes@grendel.demon.co.uk>,
Stephen Shortland <stephen@cork.cig.mot.com>,
Daniel Suman,
Jeff Uphoff <juphoff@aoc.nrao.edu>

SEE ALSO
login(1), skey(1), getuid(2), dial(3), ifconfig(8), netstat(8), route(8), setserial(8)