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+ PPP for Linux
+ -------------
+
+ Paul Mackerras
+ 8 March 2001
+
+ for ppp-2.4.2
+ Updated for ppp-2.4.5, Sep 08
+
+1. Introduction
+---------------
+
+The Linux PPP implementation includes both kernel and user-level
+parts. This package contains the user-level part, which consists of
+the PPP daemon (pppd) and associated utilities. In the past this
+package has contained updated kernel drivers. This is no longer
+necessary, as the current kernel sources contain up-to-date drivers
+(and have done since the 2.4.x kernel series).
+
+The Linux PPP implementation is capable of being used both for
+initiating PPP connections (as a `client') or for handling incoming
+PPP connections (as a `server'). Note that this is an operational
+distinction, based on how the connection is created, rather than a
+distinction that is made in the PPP protocols themselves.
+
+Mostly this package is used for PPP connections over modems connected
+via asynchronous serial ports, so this guide concentrates on this
+situation.
+
+The PPP protocol consists of two parts. One is a scheme for framing
+and encoding packets, the other is a series of protocols called LCP,
+IPCP, PAP and CHAP, for negotiating link options and for
+authentication. This package similarly consists of two parts: a
+kernel module which handles PPP's low-level framing protocol, and a
+user-level program called pppd which implements PPP's negotiation
+protocols.
+
+The kernel module assembles/disassembles PPP frames, handles error
+detection, and forwards packets between the serial port and either the
+kernel network code or the user-level program pppd. IP packets go
+directly to the kernel network code. So once pppd has negotiated the
+link, it in practice lies completely dormant until you want to take
+the link down, when it negotiates a graceful disconnect.
+
+
+2. Installation
+---------------
+
+2.1 Kernel driver
+
+Assuming you are running a recent 2.4 or 2.6 (or later) series kernel,
+the kernel source code will contain an up-to-date kernel PPP driver.
+If the PPP driver was included in your kernel configuration when your
+kernel was built, then you only need to install the user-level
+programs. Otherwise you will need to get the source tree for your
+kernel version, configure it with PPP included, and recompile. Most
+Linux distribution vendors ship kernels with PPP included in the
+configuration.
+
+The PPP driver can be either compiled into the kernel or compiled as a
+kernel module. If it is compiled into the kernel, the PPP driver is
+included in the kernel image which is loaded at boot time. If it is
+compiled as a module, the PPP driver is present in one or more files
+under /lib/modules and is loaded into the kernel when needed.
+
+The 2.2 series kernels contain an older version of the kernel PPP
+driver, one which doesn't support multilink. If you want multilink,
+you need to run a 2.4 or 2.6 series kernel. The kernel PPP driver
+was completely rewritten for the 2.4 series kernels to support
+multilink and to allow it to operate over diverse kinds of
+communication medium (the 2.2 driver only operates over serial ports
+and devices which look like serial ports, such as pseudo-ttys).
+
+Under the 2.2 kernels, if PPP is compiled as a module, the PPP driver
+modules should be present in the /lib/modules/`uname -r`/net directory
+(where `uname -r` represents the kernel version number). The PPP
+driver module itself is called ppp.o, and there will usually be
+compression modules there, ppp_deflate.o and bsd_comp.o, as well as
+slhc.o, which handles TCP/IP header compression. If the PPP driver is
+compiled into the kernel, the compression code will still be compiled
+as modules, for kernels before 2.2.17pre12. For 2.2.17pre12 and later,
+if the PPP driver is compiled in, the compression code will also.
+
+Under the 2.4 kernels, there are two PPP modules, ppp_generic.o and
+ppp_async.o, plus the compression modules (ppp_deflate.o, bsd_comp.o
+and slhc.o). If the PPP generic driver is compiled into the kernel,
+the other four can then be present either as modules or compiled into
+the kernel. There is a sixth module, ppp_synctty.o, which is used for
+synchronous tty devices such as high-speed WAN adaptors.
+
+
+2.2 User-level programs
+
+If you obtained this package in .rpm or .deb format, you simply follow
+the usual procedure for installing the package.
+
+If you are using the .tar.gz form of this package, then cd into the
+ppp-2.4.5 directory you obtained by unpacking the archive and issue
+the following commands:
+
+$ ./configure
+$ make
+# make install
+
+The `make install' has to be done as root. This makes and installs
+four programs and their man pages: pppd, chat, pppstats and pppdump.
+If the /etc/ppp configuration directory doesn't exist, the `make
+install' step will create it and install some default configuration
+files.
+
+
+2.3 System setup for 2.4 kernels
+
+Under the 2.4 series kernels, pppd needs to be able to open /dev/ppp,
+character device (108,0). If you are using udev (as most distributions
+do), the /dev/ppp node should be created by udevd.
+
+Otherwise you may need to create a /dev/ppp device node with the
+commands:
+
+# mknod /dev/ppp c 108 0
+# chmod 600 /dev/ppp
+
+
+2.4 System setup under 2.2 series kernels
+
+Under the 2.2 series kernels, you should add the following to your
+/etc/modules.conf or /etc/conf.modules:
+
+alias tty-ldisc-3 ppp
+alias ppp-compress-21 bsd_comp
+alias ppp-compress-24 ppp_deflate
+alias ppp-compress-26 ppp_deflate
+
+
+3. Getting help with problems
+-----------------------------
+
+If you have problems with your PPP setup, or you just want to ask some
+questions, or better yet if you can help others with their PPP
+questions, then you should join the linux-ppp mailing list. Send an
+email to majordomo@vger.kernel.org with a line in the body saying
+
+subscribe linux-ppp
+
+To leave the mailing list, send an email to majordomo@vger.kernel.org
+with a line in the body saying
+
+unsubscribe linux-ppp
+
+To send a message to the list, email it to linux-ppp@vger.kernel.org.
+You don't have to be subscribed to send messages to the list.
+
+You can also email me (paulus@samba.org) but I am overloaded with
+email and I can't respond to most messages I get in a timely fashion.
+
+There are also several relevant news groups, such as comp.protocols.ppp,
+comp.os.linux.networking, or comp.os.linux.setup.
+
+
+4. Configuring your dial-out PPP connections
+--------------------------------------------
+
+Some Linux distribution makers include tools in their distributions
+for setting up PPP connections. For example, for Red Hat Linux and
+derivatives, you should probably use linuxconf or netcfg to set up
+your PPP connections.
+
+The two main windowing environments for Linux, KDE and Gnome, both
+come with GUI utilities for configuring and controlling PPP dial-out
+connections. They are convenient and relatively easy to configure.
+
+A third alternative is to use a PPP front-end package such as wvdial
+or ezppp. These also will handle most of the details of talking to
+the modem and setting up the PPP connection for you.
+
+Assuming that you don't want to use any of these tools, you want to
+set up the configuration manually yourself, then read on. This
+document gives a brief description and example. More details can be
+found by reading the pppd and chat man pages and the PPP-HOWTO.
+
+We assume that you have a modem that uses the Hayes-compatible AT
+command set connected to an async serial port (e.g. /dev/ttyS0) and
+that you are dialling out to an ISP.
+
+The trickiest and most variable part of setting up a dial-out PPP
+connection is the part which involves getting the modem to dial and
+then invoking PPP service at the far end. Generally, once both ends
+are talking PPP the rest is relatively straightforward.
+
+Now in fact pppd doesn't know anything about how to get modems to dial
+or what you have to say to the system at the far end to get it to talk
+PPP. That's handled by an external program such as chat, specified
+with the connect option to pppd. Chat takes a series of strings to
+expect from the modem interleaved with a series of strings to send to
+the modem. See the chat man page for more information. Here is a
+simple example for connecting to an ISP, assuming that the ISP's
+system starts talking PPP as soon as it answers the phone:
+
+pppd connect 'chat -v "" AT OK ATDT5551212 ~' \
+ /dev/ttyS0 57600 crtscts debug defaultroute
+
+Going through pppd's options in order:
+ connect 'chat ...' This gives a command to run to contact the
+ PPP server. Here the supplied 'chat' program is used to dial a
+ remote computer. The whole command is enclosed in single quotes
+ because pppd expects a one-word argument for the 'connect' option.
+ The options to 'chat' itself are:
+
+ -v verbose mode; log what we do to syslog
+ "" don't wait for any prompt, but instead...
+ AT send the string "AT"
+ OK expect the response "OK", then
+ ATDT5551212 dial the modem, then
+ ~ wait for a ~ character, indicating the start
+ of a PPP frame from the server
+
+ /dev/ttyS0 specifies which serial port the modem is connected to
+ 57600 specifies the baud rate to use
+ crtscts use hardware flow control using the RTS & CTS signals
+ debug log the PPP negotiation with syslog
+ defaultroute add default network route via the PPP link
+
+Pppd will write error messages and debugging logs to the syslogd
+daemon using the facility name "daemon". These messages may already
+be logged to the console or to a file like /var/log/messages; consult
+your /etc/syslog.conf file to see. If you want to make all pppd
+messages go to a file such as /var/log/ppp-debug, add the line
+
+daemon.* /var/log/ppp-debug
+ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ This is one or more tabs. Do not use spaces.
+
+to syslog.conf; make sure to put one or more TAB characters (not
+spaces!) between the two fields. Then you need to create an empty
+/var/log/ppp-debug file with a command such as
+
+ touch /var/log/ppp-debug
+
+and then restart syslogd, usually by sending it a SIGHUP signal with a
+command like this:
+
+ killall -HUP syslogd
+
+
+4.1 Is the link up?
+
+The main way to tell if your PPP link is up and operational is the
+ifconfig ("interface configuration") command. Type
+
+ /sbin/ifconfig
+
+at a shell prompt. It should print a list of interfaces including one
+like this example:
+
+ppp0 Link encap Point-to-Point Protocol
+ inet addr 192.76.32.3 P-t-P 129.67.1.165 Mask 255.255.255.0
+ UP POINTOPOINT RUNNING MTU 1500 Metric 1
+ RX packets 33 errors 0 dropped 0 overrun 0
+ TX packets 42 errors 0 dropped 0 overrun 0
+
+Assuming that ifconfig shows the ppp network interface, you can test
+the link using the ping command like this:
+
+ /sbin/ping -c 3 129.67.1.165
+
+where the address you give is the address shown as the P-t-P address
+in the ifconfig output. If the link is operating correctly, you
+should see output like this:
+
+ PING 129.67.1.165 (129.67.1.165): 56 data bytes
+ 64 bytes from 129.67.1.165: icmp_seq=0 ttl=255 time=268 ms
+ 64 bytes from 129.67.1.165: icmp_seq=1 ttl=255 time=247 ms
+ 64 bytes from 129.67.1.165: icmp_seq=2 ttl=255 time=266 ms
+ --- 129.67.1.165 ping statistics ---
+ 3 packets transmitted, 3 packets received, 0% packet loss
+ round-trip min/avg/max = 247/260/268 ms
+