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Content-Centric Networking CCNx Reference Implementation

The CCNx reference implementation provides the libraries and components required to build and run applications that use and demonstrate the basic CCNx protocols for experimental and research purposes.

The protocol specifications and the reference implementation are at an early research stage of development, and are released to enable collaboration with researchers. What is provided at this time is pure infrastructure, with no applications of interest. Documentation is also minimal, and so using the release software will require technical sophistication and a willingness to read the code.

This work is free software; you can redistribute it and/or modify it under the terms of the appropriate licenses as covered in the file LICENSE and noted in each source file.

This software is distributed in hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the file LICENSE for more information.

  • Please see the file LICENSE for important licensing details and limitations.
  • Please see the file NOTICES for important notices.

For more information about Project CCNx, see our website at

This file provides introductory information in the following sections:

  1. Package contents
  2. Supported platforms and development tools
  3. Build and install instructions
  4. Running the programs
  5. Runtime files
  6. Support and contact information

README files in other directories provide platform and application-specific notes and instructions. Top-level examples include the following:


1. Package contents

This distribution includes the following things:

A. Preliminary specifications of CCNx protocol, application protocols and conventions.

B. C/POSIX reference implementation of CCNx forwarder, repository (persistent stroage of CCNx data, with synchronization), library, primitive utilities, skeleton API docs, and unit test suite. The C implementation is required for all CCNx communication.

C. Java reference implementation of library including primitive utilities, skeleton API docs, and unit test suite. The Java library has more functionality implemented or started than the C library and may be an easier place to start experimenting.

D. Minimal sample app (ccnChat) to demonstrate basic communication on local LAN.

E. Minimal sample file proxy (ccnFileProxy) to demonstrate basic communication on local LAN.

F. Experimental plugins for vlc (media transport) and wireshark (packet dissector)

G. An Android implementation for smartphones. The Android implementation has a service wrapper for ccnd and the repository. It also has a CCN Chat implementation.

Documentation is built from source files of various kinds (using a combination of doxygen and asciidoc) BUT the distribution includes pre-built documentation so it is not necessary to have a build environment and toolchain configured to start reading. Point your browser at doc/index.html to get started.

The file tree is organized as follows:

  • README - this file
  • LICENSE - license terms that apply to the distribution
  • MANIFEST - listing of every file in the distribution
  • MD5 - MD5 sum for every file in the distribution
  • NEWS - release notes
  • NOTICES - CCNx notices
  • SHA1 - SHA1 sum for every file in the distribution
  • configure - master configure script. Note that configure scripts are hand-written at this time, not generated by autoconf
  • android/ - The Android implementation
  • android/apps - Android applications that use CCNx
  • android/apps/CCNx-Android-Chat - The CCNx Chat application for Android
  • android/CCNx-Android-Lib - A common Android Library for working with CCNx
  • android/CCNx-Android-Services - Wrappers for ccnd and repository
  • android/external - External libraries needed for ARM
  • apps - experimental/sample apps tree
  • apps/ccnChat - simple text chat sample in Java
  • apps/ccnFileProxy - simple proxy making local files available via CCNx
  • apps/examples - small example programs and code snippets
  • apps/HttpProxy - sample HTTP proxy that converts HTTP Gets to CCN interests
  • apps/vlc - vlc plugin for media transport experiments
  • apps/wireshark - wireshark plugin dissector for decoding CCNx packets
  • csrc/ - C code tree
  • csrc/ccnd - CCN daemon, the user-space forwarder implementation
  • csrc/ccnr - repository daemon, for persistent storage of content
  • csrc/cmd - simple command-line utilities
  • csrc/conf - OS-specific configuration scripts etc.
  • csrc/contrib - third-party library needed for certain platforms that are POSIX-deficient
  • csrc/include/ccn - C header files
  • csrc/lib - C application library implementation
  • csrc/libexec - connectivity utilities, especially ccndc, the ccnd configurator and connectivity agent
  • csrc/rc - sample rc scripts for automatic daemon startup
  • csrc/sync - sync protocol implementation
  • csrc/tests - C test suite
  • csrc/util - launch script support
  • doc/ - documentation tree
  • doc/android - API documentation generated from Java code for Android
  • doc/ccode - API documentation generated from C code
  • doc/javacode - API documentation generated from Java code
  • doc/manpages - CCNx man pages
  • doc/technical - specifications
  • experiments/multicast - scripts for running multi-machine experiments in content distribution performance over local multicast group.
  • javasrc/ - Java code tree. The usual Java conventions are used for mapping package names to the file tree, with root package org.ccnx.ccn.
  • javasrc/lib - third-party libraries
  • javasrc/src - Java source tree
  • javasrc/tools - convenience scripts
  • schema - XML schema and DTD files
  • vendor - unmodified copies of included third-party code

After building, the following notable directories will appear:

  • bin/ - command-line tools you can run, providing convenience access to mixture of C and Java utilities and samples
  • lib/ - all libraries needed for applications (both C and Java)
  • include/ - headers needed for applications in C
  • javasrc/build - Java build outputs from ant (javasrc/bin is equivalent for Eclipse)

Note that these directories are entirely generated and will be removed by some clean targets, so don't use them for anything you want to keep.

2. Supported platforms


Only Unix-like platforms are currently supported. CCNx code is tested on Ubuntu Linux, MacOS, Solaris, and FreeBSD. Some packaging for Cygwin is currently provided but is not fully supported and there is no other support for Windows platforms yet.

Android is supported in the android/ tree. It only introduces minimal new code specific to the Android platform and otherwise re-uses the existing CCNx C and Java code.


For parts of the system written in C, you will require a standard toolchain including gcc, make. etc. and the following libraries which are not included in the distribution.

In addition, you will need vlc and wireshark to build and use the CCNx plugins for those packages. Please see the individual README files for more information.

See csrc/README* files for further notes about what needs to be installed or configured on each OS.


For parts of the system written in Java, CCNx code is tested with Java JDK 1.6 and 1.7 only, with ant used as the canonical build tool. You will need:

Eclipse .project and .classpath files are included in the distribution so you can create Eclipse projects easily that will resolve dependencies correctly. There are three Eclipse Java projects defined: one in javasrc (Eclipse project name CCNx-Java) and one each in apps/ccnChat (Eclipse project name ccnChat) and apps/ccnFileProxy (Eclipse project name ccnFileProxy). To import one of these projects into your Eclipse workspace, choose File/Import... from the menu, open the General category in the Import dialog and select "Existing Projects into Workspace". Type in (or browse to) the appropriate directory and you should see the named Project listed and selected so you can click Finish to complete the import.



You will need to use gmake rather than make.


Please see android/README for special notes about Android.


As a result of Sun Java JDK packages being removed for Ubuntu (see, we are now using OpenJDK for Ubuntu. Please see csrc/README.linux for more information.

3. Build and install instructions

Note that the overall build handles both the C and Java code, so you will need to have requirements for both met in order to avoid errors. See the section above. See android/ for information on building for Android.


In the root directory:


The top-level build will compile both C and Java code, but not Android code. The above is sufficient to run programs locally out of bin/ and build apps referencing lib/ and include/.

For users of Maven, it is now possible to build the javasrc. From the top-level:

mvn clean package

will produce a library, javadocs, and sources in separate jar files under javasrc/target. This is provided as a convenience for users of the Maven ecosystem of tools. The Maven build does not support the full suite of tests yet.


To run the complete test suite (both C and Java):

make test


To install to a standard location on your machine you may also use

make install


See the notes in the Content-Centric Networking in C in the top-level documentation.

4. Running the programs

These notes assume that you have performed the build steps listed above, but not performed a machine install. Everything may be run directly out of the build tree using programs in bin/.


All CCNx programs require that a ccnd be running:


To start ccnd sending output to a log file instead of the terminal, set the CCND_LOG environment variable with the path of the file you want to write. Any existing file with that name will be overwritten.

For a listing of other environment variables that are available (including debug message controls) run:

bin/ccnd -h

Note that you should not ordinarily run ccnd directly, but use the ccndstart script.

For experiments on one machine it is sufficient to have a ccnd running without using a ccnd configuration file, however for multiple machine experimentation you will need to use ccndc to configure the inter-machine forwarding of interest/content.

If a $HOME/.ccnx/ccnd.conf file is present then ccndstart will execute

ccndc -f $HOME/.ccnx/ccnd.conf

For a sample file, see csrc/libexec/ccnd.conf.sample


The repository provides persistent storage of CCNx content backed by a file system, and responds to interests in the content it has available.

Start a repository with the CCNR_DIRECTORY environment variable set to the fully qualified pathname of the repository file directory.


The directory named by CCNR_DIRECTORY must exist already. To start ccnr as a daemon, redirect stderr to a file and execute

bin/ccnr &

ccnr shuts down gracefully if it receives SIGINT or SIGTERM, or if the ccnd to which it is connected is shut down.

Do not run two repositories on the same backing store directory at the same time.

It is sometimes helpful to get a list of the names of stored content held by a repository. To do this, use

ccnnamelist $CCNR_DIRECTORY/repoFile1

A configuration file in $CCNR_DIRECTORY/config and/or environment variables can be used to control some settings. Most important is probably the CCNR_GLOBAL_PREFIX parameter, which is a namespace for configuration information about this repository that is expected by convention to be globally unique and meaningful, rather than only locally unique and contextually meaningful.

bin/ccnr -h

gives configuration options. For more information about repository configuration, see the ccnr man page at doc/manpages/ccnr.html.

A policy file specifies the namespaces for which the repository accepts and holds content. The name of the policy file is the concatenation of the global prefix and "data/policy.xml". The actual encoding of the files is in ccnb form, and it must be stored in the repository to take effect. Unless an alternative policy has been explicitly written/published under the policy information name, the the policy defaults to /, which means that writes will be accepted for any name and reads serviced for any name for which there is content. The command ccnrpolicyedit may be used to edit the policy. For more information about policies, see doc/technical/RepoPolicies.html.


There are a variety of simple utilities in bin/. Some of them have usage messages, but the handling of arguments and usage messages is inconsistent as of this release. Here are a few notable utilities:

  • ccnexplore - primitive GUI browser in Java, usable to browse only repo content since it requires name enumeration support available only there. Also allows writing files to repo.
  • ccnls - primitive content listing by retrieval
  • ccnlsrepo - command-line content listing from repo (via name enumeration)
  • ccnputfile - command-line tool to send file as CCNx data (asks repo to receive unless -raw arg given)
  • ccngetfile - command-line tool to retrieve CCNx content and store it in file
  • ccnchat - the ccnChat sample application
  • ccnfileproxy - the ccnFileProxy sample application

5. Runtime files

Beware that running the experimental software will create a variety of files, and that this list may not be complete:

  • ~/.ccnx - per-user directory, used primarily for personal keystore and key cache
  • ~/.rmi-server-* - per-user files Java daemon RMI interface objects. These are supposed to be cleared away automatically but that does not occur if processes are terminated manually and in other cases.

Repository directories are also created if you run a repository, but in that case you must tell the program what directory to use.

6. Support and contact information

Support for CCNx is primarily found on the mailing lists. There are three lists: (For Developers), (for Users) and (for NEW and Updates). Find out more at:

Live support can be found in realtime on IRC: #ccnx

Please see our website at

7. Contributions

For developers looking to provide bug fixes, documentation, code samples, or new features, we recommend first reviewing our process for contributing code online:

All code contributions and patches will require individuals to sign a Contributor Agreement. Individuals representing an organization should first consult with their own legal departments before singing anything. Once we have a ratified document, we are free to take in source contributions. We strongly recommend using the Fork feature of Github described here:

When code is ready for review, send a Pull Request, described here:

This process creates a nice dialogue and fosters transparency in the process.

For organizations interested in contributing large bodies of work, we recommend contacting the project leads to discuss a Software Grant Agreement.

If signing a Contributor Agreement is not possible due to organizational or legal restrictions, there are other ways to get involved, including contributing interesting code on our WIKI at:

8. Related Work

We are actively interested in promoting and fostering development and collaboration within the CCNx Community. If you have something great to share related to CCNx, built on, forked from, or otherwise of interest to this Community, please contact us. We will be looking for ways to publish community project via on our WIKI.