12 The Linux PPP implementation includes both kernel and user-level
13 parts. This package contains the user-level part, which consists of
14 the PPP daemon (pppd) and associated utilities. In the past this
15 package has contained updated kernel drivers. This is no longer
16 necessary, as the current 2.2 and 2.3 kernel sources contain
19 The Linux PPP implementation is capable of being used both for
20 initiating PPP connections (as a `client') or for handling incoming
21 PPP connections (as a `server'). Note that this is an operational
22 distinction, based on how the connection is created, rather than a
23 distinction that is made in the PPP protocols themselves.
25 Mostly this package is used for PPP connections over modems connected
26 via asynchronous serial ports, so this guide concentrates on this
29 The PPP protocol consists of two parts. One is a scheme for framing
30 and encoding packets, the other is a series of protocols called LCP,
31 IPCP, PAP and CHAP, for negotiating link options and for
32 authentication. This package similarly consists of two parts: a
33 kernel module which handles PPP's low-level framing protocol, and a
34 user-level program called pppd which implements PPP's negotiation
37 The kernel module assembles/disassembles PPP frames, handles error
38 detection, and forwards packets between the serial port and either the
39 kernel network code or the user-level program pppd. IP packets go
40 directly to the kernel network code. So once pppd has negotiated the
41 link, it in practice lies completely dormant until you want to take
42 the link down, when it negotiates a graceful disconnect.
50 Assuming you are running a recent 2.2 or 2.3 (or later) series kernel,
51 the kernel source code will contain an up-to-date kernel PPP driver.
52 If the PPP driver was included in your kernel configuration when your
53 kernel was built, then you only need to install the user-level
54 programs. Otherwise you will need to get the source tree for your
55 kernel version, configure it with PPP included, and recompile. Most
56 Linux distribution vendors ship kernels with PPP included in the
59 The PPP driver can be either compiled into the kernel or compiled as a
60 kernel module. If it is compiled into the kernel, the PPP driver is
61 included in the kernel image which is loaded at boot time. If it is
62 compiled as a module, the PPP driver is present in one or more files
63 under /lib/modules and is loaded into the kernel when needed.
65 The 2.2 series kernels contain an older version of the kernel PPP
66 driver, one which doesn't support multilink. If you want multilink,
67 you need to run the latest 2.3 series kernel. The kernel PPP driver
68 was completely rewritten for the 2.3 series kernels to support
69 multilink and to allow it to operate over diverse kinds of
70 communication medium (the 2.2 driver only operates over serial ports
71 and devices which look like serial ports, such as pseudo-ttys).
73 Under the 2.2 kernels, if PPP is compiled as a module, the PPP driver
74 modules should be present in the /lib/modules/`uname -r`/net directory
75 (where `uname -r` represents the kernel version number). The PPP
76 driver module itself is called ppp.o, and there will usually be
77 compression modules there, ppp_deflate.o and bsd_comp.o, as well as
78 slhc.o, which handles TCP/IP header compression. If the PPP driver is
79 compiled into the kernel, the compression code will still be compiled
80 as modules, for kernels before 2.2.17pre12. For 2.2.17pre12 and later,
81 if the PPP driver is compiled in, the compression code will also.
83 Under the 2.3 kernels, there are two PPP modules, ppp_generic.o and
84 ppp_async.o, plus the compression modules (ppp_deflate.o, bsd_comp.o
85 and slhc.o). If the PPP generic driver is compiled into the kernel,
86 the other four can then be present either as modules or compiled into
87 the kernel. There is a sixth module, ppp_synctty.o, which is used for
88 synchronous tty devices such as high-speed WAN adaptors.
91 2.2 User-level programs
93 If you obtained this package in .rpm or .deb format, you simply follow
94 the usual procedure for installing the package.
96 If you are using the .tar.gz form of this package, then cd into the
97 ppp-2.4.0b2 directory you obtained by unpacking the archive and issue
98 the following commands:
104 The `make install' has to be done as root. This makes and installs
105 four programs and their man pages: pppd, chat, pppstats and pppdump.
106 If the /etc/ppp configuration directory doesn't exist, the `make
107 install' step will create it and install some default configuration
111 2.3 System setup for 2.3 kernels
113 Under the 2.3 series kernels, pppd needs to be able to open /dev/ppp,
114 character device (108,0). If you are using devfs (the device
115 filesystem), the /dev/ppp node will automagically appear when the
116 ppp_generic module is loaded, or at startup if ppp_generic is compiled
119 If you have ppp_generic as a module, and you are using devfsd (the
120 devfs daemon), you will need to add a line like this to your
125 Otherwise you will need to create a /dev/ppp device node with the
128 # mknod /dev/ppp c 108 0
131 If you use module autoloading and have PPP as a module, you will need
132 to add the following to your /etc/modules.conf or /etc/conf.modules:
135 alias char-major-108 ppp_generic
136 alias tty-ldisc-3 ppp_async
137 alias tty-ldisc-14 ppp_synctty
138 alias ppp-compress-21 bsd_comp
139 alias ppp-compress-24 ppp_deflate
140 alias ppp-compress-26 ppp_deflate
143 2.4 System setup under 2.2 series kernels
145 Under the 2.2 series kernels, you should add the following to your
146 /etc/modules.conf or /etc/conf.modules:
148 alias tty-ldisc-3 ppp
149 alias ppp-compress-21 bsd_comp
150 alias ppp-compress-24 ppp_deflate
151 alias ppp-compress-26 ppp_deflate
154 3. Getting help with problems
155 -----------------------------
157 If you have problems with your PPP setup, or you just want to ask some
158 questions, or better yet if you can help others with their PPP
159 questions, then you should join the linux-ppp mailing list. Send an
160 email to majordomo@vger.rutgers.edu with a line in the body saying
164 To leave the mailing list, send an email to majordomo@vger.rutgers.edu
165 with a line in the body saying
167 unsubscribe linux-ppp
169 To send a message to the list, email it to linux-ppp@vger.rutgers.edu.
170 You don't have to be subscribed to send messages to the list.
172 You can also email me (paulus@linuxcare.com.au) but I am overloaded
173 with email and I can't respond to most messages I get in a timely
176 There are also several relevant news groups, such as comp.protocols.ppp,
177 comp.os.linux.networking, or comp.os.linux.setup.
180 4. Configuring your dial-out PPP connections
181 --------------------------------------------
183 Some Linux distribution makers include tools in their distributions
184 for setting up PPP connections. For example, for Red Hat Linux and
185 derivatives, you should probably use linuxconf or netcfg to set up
186 your PPP connections.
188 The two main windowing environments for Linux, KDE and Gnome, both
189 come with GUI utilities for configuring and controlling PPP dial-out
190 connections. They are convenient and relatively easy to configure.
192 A third alternative is to use a PPP front-end package such as wvdial
193 or ezppp. These also will handle most of the details of talking to
194 the modem and setting up the PPP connection for you.
196 Assuming that you don't want to use any of these tools, you want to
197 set up the configuration manually yourself, then read on. This
198 document gives a brief description and example. More details can be
199 found by reading the pppd and chat man pages and the PPP-HOWTO.
201 We assume that you have a modem that uses the Hayes-compatible AT
202 command set connected to an async serial port (e.g. /dev/ttyS0) and
203 that you are dialling out to an ISP.
205 The trickiest and most variable part of setting up a dial-out PPP
206 connection is the part which involves getting the modem to dial and
207 then invoking PPP service at the far end. Generally, once both ends
208 are talking PPP the rest is relatively straightforward.
210 Now in fact pppd doesn't know anything about how to get modems to dial
211 or what you have to say to the system at the far end to get it to talk
212 PPP. That's handled by an external program such as chat, specified
213 with the connect option to pppd. Chat takes a series of strings to
214 expect from the modem interleaved with a series of strings to send to
215 the modem. See the chat man page for more information. Here is a
216 simple example for connecting to an ISP, assuming that the ISP's
217 system starts talking PPP as soon as it answers the phone:
219 pppd connect 'chat -v "" AT OK ATDT5551212 ~' \
220 /dev/ttyS0 57600 crtscts debug defaultroute
222 Going through pppd's options in order:
223 connect 'chat ...' This gives a command to run to contact the
224 PPP server. Here the supplied 'chat' program is used to dial a
225 remote computer. The whole command is enclosed in single quotes
226 because pppd expects a one-word argument for the 'connect' option.
227 The options to 'chat' itself are:
229 -v verbose mode; log what we do to syslog
230 "" don't wait for any prompt, but instead...
231 AT send the string "AT"
232 OK expect the response "OK", then
233 ATDT5551212 dial the modem, then
234 ~ wait for a ~ character, indicating the start
235 of a PPP frame from the server
237 /dev/ttyS0 specifies which serial port the modem is connected to
238 57600 specifies the baud rate to use
239 crtscts use hardware flow control using the RTS & CTS signals
240 debug log the PPP negotiation with syslog
241 defaultroute add default network route via the PPP link
243 Pppd will write error messages and debugging logs to the syslogd
244 daemon using the facility name "daemon". These messages may already
245 be logged to the console or to a file like /var/log/messages; consult
246 your /etc/syslog.conf file to see. If you want to make all pppd
247 messages go to a file such as /var/log/ppp-debug, add the line
249 daemon.* /var/log/ppp-debug
250 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
251 This is one or more tabs. Do not use spaces.
253 to syslog.conf; make sure to put one or more TAB characters (not
254 spaces!) between the two fields. Then you need to create an empty
255 /var/log/ppp-debug file with a command such as
257 touch /var/log/ppp-debug
259 and then restart syslogd, usually by sending it a SIGHUP signal with a
267 The main way to tell if your PPP link is up and operational is the
268 ifconfig ("interface configuration") command. Type
272 at a shell prompt. It should print a list of interfaces including one
275 ppp0 Link encap Point-to-Point Protocol
276 inet addr 192.76.32.3 P-t-P 129.67.1.165 Mask 255.255.255.0
277 UP POINTOPOINT RUNNING MTU 1500 Metric 1
278 RX packets 33 errors 0 dropped 0 overrun 0
279 TX packets 42 errors 0 dropped 0 overrun 0
281 Assuming that ifconfig shows the ppp network interface, you can test
282 the link using the ping command like this:
284 /sbin/ping -c 3 129.67.1.165
286 where the address you give is the address shown as the P-t-P address
287 in the ifconfig output. If the link is operating correctly, you
288 should see output like this:
290 PING 129.67.1.165 (129.67.1.165): 56 data bytes
291 64 bytes from 129.67.1.165: icmp_seq=0 ttl=255 time=268 ms
292 64 bytes from 129.67.1.165: icmp_seq=1 ttl=255 time=247 ms
293 64 bytes from 129.67.1.165: icmp_seq=2 ttl=255 time=266 ms
294 --- 129.67.1.165 ping statistics ---
295 3 packets transmitted, 3 packets received, 0% packet loss
296 round-trip min/avg/max = 247/260/268 ms