8 Updated for ppp-2.4.5, Sep 08
13 The Linux PPP implementation includes both kernel and user-level
14 parts. This package contains the user-level part, which consists of
15 the PPP daemon (pppd) and associated utilities. In the past this
16 package has contained updated kernel drivers. This is no longer
17 necessary, as the current kernel sources contain up-to-date drivers
18 (and have done since the 2.4.x kernel series).
20 The Linux PPP implementation is capable of being used both for
21 initiating PPP connections (as a `client') or for handling incoming
22 PPP connections (as a `server'). Note that this is an operational
23 distinction, based on how the connection is created, rather than a
24 distinction that is made in the PPP protocols themselves.
26 Mostly this package is used for PPP connections over modems connected
27 via asynchronous serial ports, so this guide concentrates on this
30 The PPP protocol consists of two parts. One is a scheme for framing
31 and encoding packets, the other is a series of protocols called LCP,
32 IPCP, PAP and CHAP, for negotiating link options and for
33 authentication. This package similarly consists of two parts: a
34 kernel module which handles PPP's low-level framing protocol, and a
35 user-level program called pppd which implements PPP's negotiation
38 The kernel module assembles/disassembles PPP frames, handles error
39 detection, and forwards packets between the serial port and either the
40 kernel network code or the user-level program pppd. IP packets go
41 directly to the kernel network code. So once pppd has negotiated the
42 link, it in practice lies completely dormant until you want to take
43 the link down, when it negotiates a graceful disconnect.
51 Assuming you are running a recent 2.4 or 2.6 (or later) series kernel,
52 the kernel source code will contain an up-to-date kernel PPP driver.
53 If the PPP driver was included in your kernel configuration when your
54 kernel was built, then you only need to install the user-level
55 programs. Otherwise you will need to get the source tree for your
56 kernel version, configure it with PPP included, and recompile. Most
57 Linux distribution vendors ship kernels with PPP included in the
60 The PPP driver can be either compiled into the kernel or compiled as a
61 kernel module. If it is compiled into the kernel, the PPP driver is
62 included in the kernel image which is loaded at boot time. If it is
63 compiled as a module, the PPP driver is present in one or more files
64 under /lib/modules and is loaded into the kernel when needed.
66 The 2.2 series kernels contain an older version of the kernel PPP
67 driver, one which doesn't support multilink. If you want multilink,
68 you need to run a 2.4 or 2.6 series kernel. The kernel PPP driver
69 was completely rewritten for the 2.4 series kernels to support
70 multilink and to allow it to operate over diverse kinds of
71 communication medium (the 2.2 driver only operates over serial ports
72 and devices which look like serial ports, such as pseudo-ttys).
74 Under the 2.2 kernels, if PPP is compiled as a module, the PPP driver
75 modules should be present in the /lib/modules/`uname -r`/net directory
76 (where `uname -r` represents the kernel version number). The PPP
77 driver module itself is called ppp.o, and there will usually be
78 compression modules there, ppp_deflate.o and bsd_comp.o, as well as
79 slhc.o, which handles TCP/IP header compression. If the PPP driver is
80 compiled into the kernel, the compression code will still be compiled
81 as modules, for kernels before 2.2.17pre12. For 2.2.17pre12 and later,
82 if the PPP driver is compiled in, the compression code will also.
84 Under the 2.4 kernels, there are two PPP modules, ppp_generic.o and
85 ppp_async.o, plus the compression modules (ppp_deflate.o, bsd_comp.o
86 and slhc.o). If the PPP generic driver is compiled into the kernel,
87 the other four can then be present either as modules or compiled into
88 the kernel. There is a sixth module, ppp_synctty.o, which is used for
89 synchronous tty devices such as high-speed WAN adaptors.
92 2.2 User-level programs
94 If you obtained this package in .rpm or .deb format, you simply follow
95 the usual procedure for installing the package.
97 If you are using the .tar.gz form of this package, then cd into the
98 directory you obtained by unpacking the archive and issue the
105 The `make install' has to be done as root. This makes and installs
106 four programs and their man pages: pppd, chat, pppstats and pppdump.
107 If the /etc/ppp configuration directory doesn't exist, the `make
108 install' step will create it and install some default configuration
111 The ./configure script can take various optional arguments to control
112 what features are included, what directories are used for installation,
113 etc. Type "./configure --help" to see a list of options.
116 2.3 System setup for 2.4 (and later) kernels
118 Under the 2.4 series kernels, pppd needs to be able to open /dev/ppp,
119 character device (108,0). If you are using udev (as most distributions
120 do), the /dev/ppp node should be created by udevd.
122 Otherwise you may need to create a /dev/ppp device node with the
125 # mknod /dev/ppp c 108 0
129 2.4 System setup under 2.2 series kernels
131 Under the 2.2 series kernels, you should add the following to your
132 /etc/modules.conf or /etc/conf.modules:
134 alias tty-ldisc-3 ppp
135 alias ppp-compress-21 bsd_comp
136 alias ppp-compress-24 ppp_deflate
137 alias ppp-compress-26 ppp_deflate
140 3. Getting help with problems
141 -----------------------------
143 If you have problems with your PPP setup, or you just want to ask some
144 questions, or better yet if you can help others with their PPP
145 questions, then you should join the linux-ppp mailing list. Send an
146 email to majordomo@vger.kernel.org with a line in the body saying
150 To leave the mailing list, send an email to majordomo@vger.kernel.org
151 with a line in the body saying
153 unsubscribe linux-ppp
155 To send a message to the list, email it to linux-ppp@vger.kernel.org.
156 You don't have to be subscribed to send messages to the list.
158 You can also email me (paulus@ozlabs.org) but I am overloaded with
159 email and I can't respond to most messages I get in a timely fashion.
161 There are also several relevant news groups, such as comp.protocols.ppp,
162 comp.os.linux.networking, or comp.os.linux.setup.
165 4. Configuring your dial-out PPP connections
166 --------------------------------------------
168 Some Linux distribution makers include tools in their distributions
169 for setting up PPP connections. For example, for Red Hat Linux and
170 derivatives, you should probably use linuxconf or netcfg to set up
171 your PPP connections.
173 The two main windowing environments for Linux, KDE and Gnome, both
174 come with GUI utilities for configuring and controlling PPP dial-out
175 connections. They are convenient and relatively easy to configure.
177 A third alternative is to use a PPP front-end package such as wvdial
178 or ezppp. These also will handle most of the details of talking to
179 the modem and setting up the PPP connection for you.
181 Assuming that you don't want to use any of these tools, you want to
182 set up the configuration manually yourself, then read on. This
183 document gives a brief description and example. More details can be
184 found by reading the pppd and chat man pages and the PPP-HOWTO.
186 We assume that you have a modem that uses the Hayes-compatible AT
187 command set connected to an async serial port (e.g. /dev/ttyS0) and
188 that you are dialling out to an ISP.
190 The trickiest and most variable part of setting up a dial-out PPP
191 connection is the part which involves getting the modem to dial and
192 then invoking PPP service at the far end. Generally, once both ends
193 are talking PPP the rest is relatively straightforward.
195 Now in fact pppd doesn't know anything about how to get modems to dial
196 or what you have to say to the system at the far end to get it to talk
197 PPP. That's handled by an external program such as chat, specified
198 with the connect option to pppd. Chat takes a series of strings to
199 expect from the modem interleaved with a series of strings to send to
200 the modem. See the chat man page for more information. Here is a
201 simple example for connecting to an ISP, assuming that the ISP's
202 system starts talking PPP as soon as it answers the phone:
204 pppd connect 'chat -v "" AT OK ATDT5551212 ~' \
205 /dev/ttyS0 57600 crtscts debug defaultroute
207 Going through pppd's options in order:
208 connect 'chat ...' This gives a command to run to contact the
209 PPP server. Here the supplied 'chat' program is used to dial a
210 remote computer. The whole command is enclosed in single quotes
211 because pppd expects a one-word argument for the 'connect' option.
212 The options to 'chat' itself are:
214 -v verbose mode; log what we do to syslog
215 "" don't wait for any prompt, but instead...
216 AT send the string "AT"
217 OK expect the response "OK", then
218 ATDT5551212 dial the modem, then
219 ~ wait for a ~ character, indicating the start
220 of a PPP frame from the server
222 /dev/ttyS0 specifies which serial port the modem is connected to
223 57600 specifies the baud rate to use
224 crtscts use hardware flow control using the RTS & CTS signals
225 debug log the PPP negotiation with syslog
226 defaultroute add default network route via the PPP link
228 Pppd will write error messages and debugging logs to the syslogd
229 daemon using the facility name "daemon". These messages may already
230 be logged to the console or to a file like /var/log/messages; consult
231 your /etc/syslog.conf file to see. If you want to make all pppd
232 messages go to a file such as /var/log/ppp-debug, add the line
234 daemon.* /var/log/ppp-debug
235 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
236 This is one or more tabs. Do not use spaces.
238 to syslog.conf; make sure to put one or more TAB characters (not
239 spaces!) between the two fields. Then you need to create an empty
240 /var/log/ppp-debug file with a command such as
242 touch /var/log/ppp-debug
244 and then restart syslogd, usually by sending it a SIGHUP signal with a
252 The main way to tell if your PPP link is up and operational is the
253 ifconfig ("interface configuration") command. Type
257 at a shell prompt. It should print a list of interfaces including one
260 ppp0 Link encap Point-to-Point Protocol
261 inet addr 192.76.32.3 P-t-P 129.67.1.165 Mask 255.255.255.0
262 UP POINTOPOINT RUNNING MTU 1500 Metric 1
263 RX packets 33 errors 0 dropped 0 overrun 0
264 TX packets 42 errors 0 dropped 0 overrun 0
266 Assuming that ifconfig shows the ppp network interface, you can test
267 the link using the ping command like this:
269 /sbin/ping -c 3 129.67.1.165
271 where the address you give is the address shown as the P-t-P address
272 in the ifconfig output. If the link is operating correctly, you
273 should see output like this:
275 PING 129.67.1.165 (129.67.1.165): 56 data bytes
276 64 bytes from 129.67.1.165: icmp_seq=0 ttl=255 time=268 ms
277 64 bytes from 129.67.1.165: icmp_seq=1 ttl=255 time=247 ms
278 64 bytes from 129.67.1.165: icmp_seq=2 ttl=255 time=266 ms
279 --- 129.67.1.165 ping statistics ---
280 3 packets transmitted, 3 packets received, 0% packet loss
281 round-trip min/avg/max = 247/260/268 ms