The Multipath TCP Daemon - mptcpd - is a daemon for Linux based operating systems that performs multipath TCP path management related operations in the user space. It interacts with the Linux kernel through a generic netlink connection to track per-connection information (e.g. available remote addresses), available network interfaces, request new MPTCP subflows, handle requests for subflows, etc.

By default, this daemon will load the addr_adv plugin, which will add MPTCP endpoints with the subflow flag ("client" mode) for the default in-kernel path-manager. Note that this is something NetworkManager 1.40 or newer does by default. Having several daemons configuring the MPTCP endpoints at the same time should be avoided. This daemon is usually recommended when NetworkManager 1.40 or newer is not available, or when advanced per-connection path management is needed, using the userspace path-manager and a custom made plugin using the C API.

To change this behavior, with NetworkManager, look for the connection.mptcp-flags option in the settings, while for mptcpd, look at the /etc/mptcpd/mptcpd.conf config file, or disable the service if it is not needed. Make sure not to have both NetworkManager and mptcpd conflicting to configure the MPTCP endpoints.

mptcpd is packaged in most major distributions:

Do not hesitate to help with the packaging.

mptcpd is built in much the same way most Autotool-enabled software packages are built. This includes the build approach for both clones of the mptcpd Git repository and self-contained mptcpd release tar archive (e.g. mptcpd-0.1.tar.gz).

Build dependencies for mptcpd vary depending on whether or not you are building from a self-contained maintainer generated mptcpd tar archive or from a cloned Git mptcpd repository, for example.

• Basic mptcpd Build Dependencies
  • C compiler (C99 compliant)
  • Embedded Linux Library >= v0.30
  • Argp library (either the GNU libc built-in or standalone)
  • Linux kernel MPTCP user API headers
  • pkg-config
• Additional Build Dependencies for Maintainers, and mptcpd Git Repository Clones
  • GNU Autoconf
  • GNU Automake
  • GNU Libtool
  • GNU Autoconf Archive
  • Pandoc >= 2.2.1 (needed to convert README.md contents from the GitHub markdown format content to plain text)
  • Doxygen (only needed to build documentation)

Bootstrapping the mptcpd source distribution is only necessary when building a clone of the mptcpd Git repository for the first time, or possibly after making modifications to the mptcpd build infrastructure (e.g. configure Makefile, etc). There is no need to bootstrap self-contained mptcpd releases generated by the canonical make dist command.

Assuming all maintainer related build dependencies listed above are installed, bootstrapping mptcpd simply requires running the bootstrap script in the top-level source directory, e.g.:

$ ./bootstrap

Move on to the common build steps below once bootstrapping is complete.

mptcpd shares the usual build procedure found in all Autotool enabled software packages, i.e. running the configure script in the desired build directory, and running make afterward:

./configure make

or for an alternate build directory:

mkdir the_build cd the_build ../configure make

Run configure --help to list all command line build configuration options. Further generic configuration and build details may be found in the INSTALL file.

Unit tests included in the mptcpd source distribution may be run like so:

./configure make check

Once again, these steps may be performed in an alternate build directory.

Whether or not debugging support (e.g. debug symbols) is compiled by default into mptcpd binaries depends on how the mptcpd source was obtained, i.e. as a cloned git repository or as a "released" tar archive. It boils downs to the existence of a ".git" directory in the top level mptcpd source directory. Debug symbols will be enabled and optimization disabled by default if such a directory exists, and vice versa if doesn't exist. The default behavior may be overriden by using the --enable-debug configuration option:

 --enable-debug=[yes/info/profile/no] compile with debugging 

The usual build flags, such as CFLAGS, LDFLAGS, etc, may be provided on the configure script command line. See the output from ./configure --help, or the INSTALL file, for additional details.

To aid with identifying areas of the mptcpd code that are or are not exercised by its unit tests or when deployed, mptcpd may be instrumented for code coverage when it is built with GCC. Code coverage reports will also require the tools gcov, lcov and genhtml to be installed as well.

To enable mptcpd code coverage instrumentation, and generate reports from unit tests in the top level source directory, for example, build mptcpd like so:

./configure --enable-code-coverage make check-code-coverage

The location of the HTML formatted code coverage results will be displayed after the report is generated.

HTML formatted code documentaton for mptcpd may be generated if Doxygen is installed by running the doxygen-doc make target, e.g.:

./configure make doxygen-doc

Generated documentation will be placed in the doc/html directory. PostScript and PDF formatted documentation generation is disabled by default but may be explicitly generated using the doxygen-ps and doxygen-pdf make targets.

Additional Doxygen based documentation generation options are described in the configure script help output (e.g. ./configure --help).

The mptcpd source package provides the same installation related make targets found in most GNU style and Autotool enabled software packages. The most basic way to install mptcpd is:

make install

By default mptcpd will be installed in appropriate directories under the directory /usr/local. Fine tuning of installation directories may be done using several configure script command line options. See the help output from ./configure --help as well as the INSTALL file for details.

Super user (root) permissions may be necessary if installing into directories owned by root.

If systemd is detected a service file will be installed in the appropriate location (e.g. /lib/systemd/system). That installation directory is independendent of the default directories mentioned above. If necessary, the systemd service file installation directory may be changed using the following configure script command line option.

 --with-systemdsystemunitdir=DIR Directory for systemd service files 

mptcpd may be started in a number of ways depending on whether or not systemd is used to run installed binaries, or if it is run directly from the source tree (e.g. when debugging development versions) without installation.

mptcpd currently does not provide traditional System V "init scripts". In general the mptcpd program may be run directly from the installed directory, e.g.:

/usr/bin/mptcpd

However, it may be necessary to explicitly set the library load path through the LD_LIBRARY_PATH environment path if mptcpd is installed in a set of directories unknown to the dynamic linker, e.g.:

LD_LIBRARY_PATH=/usr/local/lib:$LD_LIBRARY_PATH /usr/local/bin/mptcpd

or:

# Assumes Bourne shell style environment variable assignment. export LD_LIBRARY_PATH=/usr/local/lib:$LD_LIBRARY_PATH /usr/local/bin/mptcpd

Alternatively, update the dynamic linker run-time bindings by running ldconfig after installation of mptcpd.

NOTE: mptcpd requires the CAP_NET_ADMIN capability to be fully functional. If not using the provided systemd service file mptcp.service, the necessary capability may be granted to mptcpd by any of the following:

• Run as root (generally not desirable)
• Run with a wrapper such as, capsh
• Attach the required capabilities to the installed mptcpd executable through setcap

To start mptcpd immediately after installation using systemd run the following commands:

systemctl daemon-reload systemctl start mptcp.service

These steps are not necessary if the system is rebooted after installation of mptcpd.

Since mptcpd is built with libtool support it is generally best to execute mptcpd using libtool. For example, to run mptcpd under the gdb debugger one could do the following, assuming mptcpd was configured and built from the top level source directory:

./libtool --mode=execute gdb ./src/mptcpd 

Further help is available through the Linux kernel MPTCP community:

• E-mail: MPTCP mailing list
• IRC: #mptcp on Libera.Chat