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WiMoVE - Wireless Mobility through VXLAN EVPN

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WiMoVE is a scalable Wi-Fi System that partitions all stations in separate overlay L2 domains to limit the amount of wireless L2 broadcast traffic. In large Wi-Fi systems, broadcast traffic can take up large amounts of airtime. A great talk that explains the problem in more detail is available here. In WiMoVE, overlay L2 domains "follow" the stations, being resized on demand, thus preserving handover.

WiMoVE is built with standard network protocols, on top of open‑source technology:

  • The overlay networks use BGP EVPN with VXLAN encapsulation.
  • All BGP speakers run FRRouting to exchange EVPN routes.
  • The access points run OpenWrt with our custom, open‑source daemon called wimoved.

This solution allows for using commodity access points running OpenWrt for large‑scale Wi‑Fi deployments, even from different vendors.

WiMoVE consists of multiple parts. If you want to learn more about the architecture or create a full setup, take a look at our documentation.

This repository

This repository contains the WiMoVE Access Point daemon wimoved. The daemon is reponsible for connecting 802.11 stations to BGP EVPN. This is achieved by letting hostapd create one interface per station (see below), creating VXLAN interfaces and bridging the interfaces.

The following diagram shows the components and their interactions:

The daemon is responsible for handling hostapd events, creating VXLAN interfaces and bridges. FRR receives events whenever network interfaces change and advertises the corresponding reachability information using BGP EVPN.

Supported architectures

Currently, we support OpenWrt with the architectures ramips-mt7621 and mvebu-cortexa9. We test our software on the Access Point models ZyXEL NWA50AX and Linksys WRT1900ACS. If you need support for other OpenWrt architectures, feel free to open an issue.

Development setup

The development setup is an easy way to test wimoved. Please be aware that after following this guide, you do not have a full WiMoVE installation. You can connect to the Wi-Fi but won't be connected to other devices or the Internet. If you want a complete WiMoVE setup, follow the setup guide instead. Currently, we only support Linux as a development platform.

Setup hostapd

First, we will set up hostapd.

  • Install hostapd using your distribution's package manager. Alternatively, you can build it from source, see here. By default, hostapd comes with VLAN support. If you encounter issues, make sure that it was compiled with CONFIG_NO_VLAN=n.
  • Put the following in your /etc/hostapd.conf, replacing the placeholder values:
    interface=<interface>
    ssid=<ssid>
    ieee80211d=1
    country_code=<Your country code>
    hw_mode=g
    ieee80211n=1
    channel=6
    beacon_int=1000
    dtim_period=2
    max_num_sta=255
    rts_threshold=-1
    fragm_threshold=-1
    macaddr_acl=0
    auth_algs=1
    ignore_broadcast_ssid=0
    wmm_enabled=0
    eapol_key_index_workaround=0
    eap_server=0
    wpa=2
    wpa_key_mgmt=WPA-PSK
    rsn_pairwise=CCMP
    wpa_passphrase=<Secret key>
    per_sta_vif=1
    vlan_file=/etc/hostapd/hostapd.vlan
  • Create a file /etc/hostapd/hostapd.vlan with the following content:
*   vlan#
  • Hostapd has to be started with the option -g /var/run/hostapd/global. For the service to work properly, you might have to edit the service file for hostapd. Run systemctl status hostapd to locate this file.
  • Start hostapd, either with systemctl start hostapd or on the command line. You might need to stop NetworkManager before starting hostapd since the programs interfere with each other.

Build

  • Install libnl. On a recent Linux system, the corresponding package is probably already installed.
  • Install prometheus-cpp.
    • On Ubuntu, install the package prometheus-cpp-dev.
    • On Arch Linux, the package is available in the AUR as prometheus-cpp-git.
  • Clone the repository by running git clone https://github.com/WiMoVE-OSS/wimoved.
  • Build the project by running cmake . followed by make -j$(nproc).
  • Start wimoved by running ./wimoved.

Coding guidelines

Format the source files by running make format. Lint the source files by running make lint. Build the tests by running make test. Run both checks and the tests by doing make precommit. The coding guidelines are enforced via the CI pipeline.

As linting takes a long time, we recommend integrating clang-tidy into your editor.

Sanitization

Build with sanitizers enabled by running cmake . -DWIMOVED_SANITIZE=ON. For full stacktrace support, set the environment variable LSAN_OPTIONS=fast_unwind_on_malloc=0:malloc_context_size=30.

Build for OpenWrt

OpenWrt packages are built on every release. On each commit on main, a pre-release is created and a build is triggered. You can download the packages on the releases page.

The pipeline works as follows:

  • For both supported architectures (mvebu-cortexa9, ramips-mt7621), there is a Docker image containing an OpenWrt build environment. In the image, libnl and prometheus-cpp are already built. The corresponding Dockerfile is located in docker/openwrt-build-env.
  • The pipeline sets the environment variable IMAGE and runs openwrt/build-openwrt.sh. This creates a container from the image, mounting the source code and the output directory.
  • The packages from the output directory are uploaded as pipeline artifacts.

If you want to build for OpenWrt locally, you first need to build or pull a base image. Base images can be found on the Packages page. Then, you can run ./openwrt/build-openwrt.sh:

export IMAGE=ghcr.io/wimove-oss/wimove/wimove-buildenv/mvebu-cortexa9-22.03.3:main
docker pull "$IMAGE"
./openwrt/build-openwrt.sh

The script creates an out directory and the package will be inside that directory.

Configuration

The default configuration file is /etc/wimoved/config. A different configuration file can be specified as the first argument, i.e. by running wimoved /path/to/config. The following configuration options are available:

Name Default Explanation
hapd_sockdir /var/run/hostapd Socket directory for hostapd. Hostapd sockets are discovered automatically from this directory.
hapd_group root Group under which hostapd is run. This is needed to set the appropriate permissions when communicating with hostapd. On OpenWrt, this must be "network".
log_path wimoved.log Path to the log file when logging to a file. Does nothing if logging to syslog.
cleanup_interval 10 Duration of the cleanup timer (seconds). Wimoved removes interfaces whenever the cleanup timer expires.
min_vni 1 Minimum VNI used for hashing station MACs to VNIs
max_vni 20 Maximum VNI used for hashing station MACs to VNIs (exclusive)
sockets Explicit list of hostapd sockets, comma-separated. If used, hapd_sockdir will not be scanned for sockets. Names are relative to hapd_sockdir.

Monitoring and Logging

Monitoring

wimoved exposes metrics via prometheus on port 9500. Via the endpoint, information on how many stations are associated, how many events have been handled and how long the event handling took is exposed. The endpoint is activated by default. We plan on making the endpoint optional via a config option.

Logging

Wimoved can log to a file or to syslog.

The file can be set through the configuration option log_path.

On OpenWrt, wimoved logs to syslog. This is done by defining ELPP_SYSLOG in CMakeLists.txt. A syslog aggregator like syslog-ng can be used to aggregate those logs on a different host.

Known Issues

  • When a station roams from one AP to another, zebra can get into a state where no packets are forwarded to the station. We track the issue as #68. The cause seems to be an upstream issue in FRR which we reported here.