libnetconf2 – The NETCONF protocol library

libnetconf2 is a NETCONF library in C intended for building NETCONF clients and servers. NETCONF is the NETwork CONFiguration protocol introduced by IETF.

libnetconf2 is a NETCONF library in C handling NETCONF authentication and all NETCONF RPC communication both server and client-side. Note that NETCONF datastore implementation is not a part of this library. The library supports both NETCONF 1.0 (RFC 4741) as well as NETCONF 1.1 (RFC 6241). The main features include:

• NETCONF over SSH (RFC 4742, RFC 6242), using libssh.
• NETCONF over TLS (RFC 7589), using OpenSSL.
  • DNSSEC SSH Key Fingerprints (RFC 4255)
• NETCONF over pre-established transport sessions (using this mechanism the communication can be tunneled through sshd(8), for instance).
• NETCONF Call Home (RFC 8071).
• NETCONF Event Notifications (RFC 5277).
• Compatibility with the ietf-netconf-server YANG module.

libnetconf2 is maintained and further developed by the Tools for Monitoring and Configuration department of CESNET. Any testing or improving/fixing the library is welcome. Please inform us about your experiences with using libnetconf2 via the issue tracker.

Besides the libyang, libnetconf2 is another basic building block for the Netopeer2 toolset. For a reference implementation of NETCONF client and server, check the Netopeer2 project.

Branches

The project uses 2 main branches master and devel. Other branches should not be cloned. In master there are files of the last official release. Any latest improvements and changes, which were tested at least briefly are found in devel. On every new release, devel is merged into master.

This means that when only stable official releases are to be used, either master can be used or specific releases downloaded. If all the latest bugfixes should be applied, devel branch is the one to be used. Note that whenever a new issue is created and it occurs on the master branch, the first response will likely be to use devel before any further provided support.

libnetconf vs libnetconf2

libnetconf2 was developed with experiences gained from the development of the libnetconf library, which is now obsolete and should not be used.

Packages

Binary RPM or DEB packages of the latest release can be built locally using apkg, look into README in the distro directory.

Requirements

• C compiler (gcc >= 4.8.4, clang >= 3.0, ...)
• cmake >= 3.5.0
• crypt(3)
• libyang
• libssh >= 0.9.5 (for SSH support)
• OpenSSL >= 3.0.0 (for TLS support)
• curl >= 7.30.0

Optional

• libpam (for PAM-based SSH keyboard-interactive authentication method)
• libval (only for DNSSEC SSHFP retrieval)
  • DNSSEC-Tools/dnssec-tools/validator part of the DNSSEC-Tools suite
• doxygen (for generating documentation)
• cmocka >= 1.0.1 (for tests only, see Tests)
• valgrind (for enhanced testing)
• gcov (for code coverage)
• lcov (for code coverage)
• genhtml (for code coverage)

Building

$ mkdir build; cd build
$ cmake ..
$ make
# make install

The library documentation can be generated directly from the source codes using Doxygen tool:

$ make doc

Build Options

There are various options to change result of building.

Changing Compiler

Set CC environment variable:

$ CC=/usr/bin/clang cmake ..

Installation Prefix

By default, the library is installed with the /usr/local prefix, to change it, use the following option:

$ cmake -DCMAKE_INSTALL_PREFIX:PATH=/usr ..

Transport Protocol Support

The NETCONF protocol specification allows to use the protocol on top of several transport protocols. libnetconf2 provides support for SSH and TLS transport. By default, both SSH and TLS transport is enabled. Disabling and enabling both the transport protocols can be made in the same way. The following command has actually the same effect as specifying no option since it specifies the default settings.

$ cmake -DENABLE_SSH_TLS=ON ..

DNSSEC SSHFP Retrieval

In SSH connections, if the remote NETCONF server supports it and it is enabled, it is possible to safely retrieve server host key fingerprints using DNSSEC and automatically consider them to be trusted without any interaction. Enable it with the following command.

$ cmake -DENABLE_DNSSEC=ON ..

Build Modes

There are two build modes:

• Release. This generates library for the production use without any debug information.
• Debug. This generates library with the debug information and disables optimization of the code.

The Debug mode is currently used as the default one. to switch to the Release mode, enter at the command line:

$ cmake -D CMAKE_BUILD_TYPE:String="Release" ..

Inactive Read Timeout

It is possible to adjust inactive read timeout. It is used when a new message is being read and no new data had arrived for this amount of seconds. 20 is the default value.

$ cmake -D READ_INACTIVE_TIMEOUT:String="20" ..

Active Read Timeout

Active read timeout is used to limit the maximum number of seconds a message is given to arrive in its entirety once a beginning is read. The default is 300 (5 minutes).

$ cmake -D READ_ACTIVE_TIMEOUT:String="300" ..

PSPoll Thread Count

This value limits the maximum number of threads that can concurrently access (wait for access) a single pspoll structure. To simplify, how many threads could simultaneously call a function whose parameter is one and the same pspoll structure. If using netopeer2-server, it will warn that this value needs to be adjusted if too small.

$ cmake -D MAX_PSPOLL_THREAD_COUNT:String="6" ..

Code Coverage

Based on the tests run, it is possible to generate code coverage report. But it must be enabled and these commands are needed to generate the report:

$ cmake -DENABLE_COVERAGE=ON ..
$ make
$ make coverage

Note that gcc compiler is required for this option.

CMake Notes

Note that, with CMake, if you want to change the compiler or its options after you already ran CMake, you need to clear its cache first - the most simple way to do it is to remove all content from the 'build' directory.

Usage

All public functions are available via 2 headers:

#include <nc_server.h>
#include <nc_client.h>

You need to include either one if implementing a NETCONF server or a NETCONF client, respectively.

To compile your program with libnetconf2, it is necessary to link it with it using the following linker parameters:

-lnetconf2

Examples

See examples directory for an example client and server.

Tests

The repository includes several tests built with cmocka. The tests can be found in tests subdirectory and they are designed for checking library functionality after code changes.

The tests are by default built in the Debug build mode by running

$ make

In case of the Release mode, the tests are not built by default (it requires additional dependency), but it can be enabled via cmake option:

$ cmake -DENABLE_TESTS=ON ..

Note that if the necessary cmocka headers are not present in the system include paths, tests are not available despite the build mode or cmake's options.

Tests can be run by the make's test target:

$ make test