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paulusmack / ppp

PPP daemon and associated utilities

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This is the README file for ppp-2.4, a package which implements the Point-to-Point Protocol (PPP) to provide Internet connections over serial lines.


The Point-to-Point Protocol (PPP) provides a standard way to establish a network connection over a serial link. At present, this package supports IP and IPV6 and the protocols layered above them, such as TCP and UDP. The Linux port of this package also has support for IPX.

This PPP implementation consists of two parts:

  • Kernel code, which establishes a network interface and passes packets between the serial port, the kernel networking code and the PPP daemon (pppd). This code is implemented using STREAMS modules on Solaris, and as a line discipline under Linux.

  • The PPP daemon (pppd), which negotiates with the peer to establish the link and sets up the ppp network interface. Pppd includes support for authentication, so you can control which other systems may make a PPP connection and what IP addresses they may use.

The platforms supported by this package are Linux and Solaris. I have code for NeXTStep, FreeBSD, SunOS 4.x, SVR4, Tru64 (Digital Unix), AIX and Ultrix but no active maintainers for these platforms. Code for all of these except AIX is included in the ppp-2.3.11 release.

The kernel code for Linux is no longer distributed with this package, since the relevant kernel code is in the official Linux kernel source (and has been for many years) and is included in all reasonably modern Linux distributions. The Linux kernel code supports using PPP over things other than serial ports, such as PPP over Ethernet and PPP over ATM.


The file SETUP contains general information about setting up your system for using PPP. There is also a README file for each supported system, which contains more specific details for installing PPP on that system. The supported systems, and the corresponding README files, are:

Linux               README.linux
Solaris             README.sol2

In each case you start by running the ./configure script. This works out which operating system you are using and creates the appropriate makefiles. You then run

make' to compile the user-level code, and
(as root)
make install' to install the user-level programs pppd, chat and pppstats.

N.B. Since 2.3.0, leaving the permitted IP addresses column of the pap-secrets or chap-secrets file empty means that no addresses are permitted. You need to put a "*" in that column to allow the peer to use any IP address. (This only applies where the peer is authenticating itself to you, of course.)

What's new in ppp-2.4.8.

  • New pppd options have been added:

    • ifname, to set the name for the PPP interface device
    • defaultroute-metric, to set the metric for the default route
    • defaultroute6, to add an IPv6 default route (with nodefaultroute6 to prevent adding an IPv6 default route)
    • up_sdnotify, to have pppd notify systemd when the link is up.
  • The rp-pppoe plugin has new options:

    • host-uniq, to set the Host-Uniq value to send
    • pppoe-padi-timeout, to set the timeout for discovery packets
    • pppoe-padi-attempts, to set the number of discovery attempts.
  • Added the CLASS attribute in radius packets.

  • Sundry bug fixes.

  • Fixed warnings and issues found by static analysis.

  • Added Submitting-patches.md.

What was new in ppp-2.4.7.

  • Fixed a potential security issue in parsing option files (CVE-2014-3158).

  • There is a new "stop-bits" option, which takes an argument of 1 or 2, indicating the number of stop bits to use for async serial ports.

  • Various bug fixes.

What was new in ppp-2.4.6.

  • Man page updates.

  • Several bug fixes.

  • Options files can now set and unset environment variables for scripts.

  • The timeout for chat scripts can now be taken from an environment variable.

  • There is a new option, master_detach, which allows pppd to detach from the controlling terminal when it is the multilink bundle master but its own link has terminated, even if the nodetach option has been given.

What was new in ppp-2.4.5.

  • Under Linux, pppd can now operate in a mode where it doesn't request the peer's IP address, as some peers refuse to supply an IP address. Since Linux supports device routes as well as gateway routes, it's possible to have no remote IP address assigned to the ppp interface and still route traffic over it.

  • Pppd now works better with 3G modems that do strange things such as sending IPCP Configure-Naks with the same values over and over again.

  • The PPP over L2TP plugin is included, which works with the pppol2tp PPP channel code in the Linux kernel. This allows pppd to be used to set up tunnels using the Layer 2 Tunneling Protocol.

  • A new 'enable-session' option has been added, which enables session accounting via PAM or wtwp/wtmpx, as appropriate. See the pppd man page for details.

  • Several bugs have been fixed.

What was new in ppp-2.4.4.

  • Pppd will now run /etc/ppp/ip-pre-up, if it exists, after creating the ppp interface and configuring its IP addresses but before bringing it up. This can be used, for example, for adding firewall rules for the interface.

  • Lots of bugs fixed, particularly in the area of demand-dialled and persistent connections.

  • The rp-pppoe plugin now accepts any interface name (that isn't an existing pppd option name) without putting "nic-" on the front of it, not just eth, nas, tap* and br*.

What was new in ppp-2.4.3.

  • The configure script now accepts --prefix and --sysconfdir options. These default to /usr/local and /etc. If you want pppd put in /usr/sbin as before, use ./configure --prefix=/usr.

  • Doing

    make install' no longer puts example configuration files in
    /etc/ppp.  Use
    make install-etcppp' if you want that.
  • The code has been updated to work with version 0.8.3 of libpcap. Unfortunately the libpcap maintainers removed support for the "inbound" and "outbound" keywords on PPP links, meaning that if you link pppd with libpcap-0.8.3, you can't use those keywords in the active-filter and pass-filter expressions. The support has been reinstated in the CVS version and should be in future libpcap releases. If you need the in/outbound keywords, use a later release than 0.8.3, or get the CVS version from http://www.tcpdump.org.

  • There is a new option, child-timeout, which sets the length of time that pppd will wait for child processes (such as the command specified with the pty option) to exit before exiting itself. It defaults to 5 seconds. After the timeout, pppd will send a SIGTERM to any remaining child processes and exit. A value of 0 means no timeout.

  • Various bugs have been fixed, including some CBCP packet parsing bugs that could lead to the peer being able to crash pppd if CBCP support is enabled.

  • Various fixes and enhancements to the radius and rp-pppoe plugins have been added.

  • There is a new winbind plugin, from Andrew Bartlet of the Samba team, which provides the ability to authenticate the peer against an NT domain controller using MS-CHAP or MS-CHAPV2.

  • There is a new pppoatm plugin, by various authors, sent in by David Woodhouse.

  • The multilink code has been substantially reworked. The first pppd for a bundle still controls the ppp interface, but it doesn't exit until all the links in the bundle have terminated. If the first pppd is signalled to exit, it signals all the other pppds controlling links in the bundle.

  • The TDB code has been updated to the latest version. This should eliminate the problem that some people have seen where the database file (/var/run/pppd.tdb) keeps on growing. Unfortunately, however, the new code uses an incompatible database format. For this reason, pppd now uses /var/run/pppd2.tdb as the database filename.

What was new in ppp-2.4.2.

  • The CHAP code has been rewritten. Pppd now has support for MS-CHAP V1 and V2 authentication, both as server and client. The new CHAP code is cleaner than the old code and avoids some copyright problems that existed in the old code.

  • MPPE (Microsoft Point-to-Point Encryption) support has been added, although the current implementation shouldn't be considered completely secure. (There is no assurance that the current code won't ever transmit an unencrypted packet.)

  • James Carlson's implementation of the Extensible Authentication Protocol (EAP) has been added.

  • Support for the Encryption Control Protocol (ECP) has been added.

  • Some new plug-ins have been included:

    • A plug-in for kernel-mode PPPoE (PPP over Ethernet)
    • A plug-in for supplying the PAP password over a pipe from another process
    • A plug-in for authenticating using a Radius server.
  • Updates and bug-fixes for the Solaris port.

  • The CBCP (Call Back Control Protocol) code has been updated. There are new options

    remotenumber' and
  • Extra hooks for plugins to use have been added.

  • There is now a `maxoctets' option, which causes pppd to terminate the link once the number of bytes passed on the link exceeds a given value.

  • There are now options to control whether pppd can use the IPCP IP-Address and IP-Addresses options:

    ipcp-no-address' and
  • Fixed several bugs, including potential buffer overflows in chat.

What was new in ppp-2.4.1.

  • Pppd can now print out the set of options that are in effect. The new

    dump' option causes pppd to print out the option values after
    option parsing is complete.  The
    dryrun' option causes pppd to print the options and then exit.
  • The option parsing code has been fixed so that options in the per-tty options file are parsed correctly, and don't override values from the command line in most cases.

  • The plugin option now looks in /usr/lib/pppd/ (for example, /usr/lib/pppd/2.4.1b1) for shared objects for plugins if there is no slash in the plugin name.

  • When loading a plugin, pppd will now check the version of pppd for which the plugin was compiled, and refuse to load it if it is different to pppd's version string. To enable this, the plugin source needs to #include "pppd.h" and have a line saying: char pppd_version[] = VERSION;

  • There is a bug in zlib, discovered by James Carlson, which can cause kernel memory corruption if Deflate is used with the lowest setting,

    1. As a workaround pppd will now insist on using at least 9.
  • Pppd should compile on Solaris and SunOS again.

  • Pppd should now set the MTU correctly on demand-dialled interfaces.

What was new in ppp-2.4.0.

  • Multilink: this package now allows you to combine multiple serial links into one logical link or `bundle', for increased bandwidth and reduced latency. This is currently only supported under the 2.4.x and later Linux kernels.

  • All the pppd processes running on a system now write information into a common database. I used the `tdb' code from samba for this.

  • New hooks have been added.

For a list of the changes made during the 2.3 series releases of this package, see the Changes-2.3 file.

Compression methods.

This package supports two packet compression methods: Deflate and BSD-Compress. Other compression methods which are in common use include Predictor, LZS, and MPPC. These methods are not supported for two reasons - they are patent-encumbered, and they cause some packets to expand slightly, which pppd doesn't currently allow for. BSD-Compress and Deflate (which uses the same algorithm as gzip) don't ever expand packets.


The comp.protocols.ppp newsgroup is a useful place to get help if you have trouble getting your ppp connections to work. Please do not send me questions of the form "please help me get connected to my ISP" - I'm sorry, but I simply do not have the time to answer all the questions like this that I get.

If you find bugs in this package, please report them to the maintainer for the port for the operating system you are using:

Linux Paul Mackerras [email protected] Solaris James Carlson [email protected]


All of the code can be freely used and redistributed. The individual source files each have their own copyright and permission notice. Pppd, pppstats and pppdump are under BSD-style notices. Some of the pppd plugins are GPL'd. Chat is public domain.


The primary site for releases of this software is:


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