Wi-Fi: OpenBSD

Added: 2024-01

The OpenBSD Wi-Fi source captures from Wi-Fi interfaces on OpenBSD, using the net80211 monitor mode support and libpcap.

The OpenBSD Wi-Fi source is still under development, and has significant limitations; see Limitations below.

The source should be configured with the type set explicitly:

source=iwm0:type=openbsdwifi

Supported hardware

Any OpenBSD Wi-Fi interface supporting monitor mode can be used. Interfaces in the wlan interface group are listed as available sources.

Compiling OpenBSD Wi-Fi support

OpenBSD Wi-Fi support is built automatically when compiling Kismet on OpenBSD, and requires libpcap.

The capture tool must run as root to control the interface; install it with make suidinstall, or run Kismet as root.

On other platforms the OpenBSD Wi-Fi source can only be used as a remote capture from an OpenBSD system.

Kismet OpenBSD Wi-Fi support

When the source is opened, Kismet places the interface in monitor mode and brings it up. Kismet also assigns a random MAC address to the interface.

Packets are captured with radiotap headers and processed as normal 802.11 frames.

OpenBSD Wi-Fi source parameters

Naming and description options

All data sources accept the common naming and description options.

Channel options

The OpenBSD Wi-Fi source supports the common channel and hopping options. The channel list is read from the interface.

channel={ channel number }

The channel to tune to when the source opens.

Filtering options

filter_mgmt={ true } / { false }

Only capture management frames and EAPOL frames.

truncate_data={ true } / { false }

Truncate data frames to the 802.11 header, while keeping EAPOL frames.

Debugging options

verbose={ true } / { false }

Report when setting a channel takes longer than 100ms.

statistics={ true } / { false }

Report the average time taken to set the channel, every 100 channel changes.

Limitations

The OpenBSD Wi-Fi source currently has these limitations:

  • Only 2.4GHz channels are tuned correctly. HT and VHT channels (such as 6HT40+) are not supported.
  • The ht_channels, vht_channels, default_ht20, expand_ht20, band24ghz, band5ghz, and band6ghz options are accepted for compatibility with the Linux Wi-Fi source, but have no effect.
  • The filter_locals, filter_interface, and filter_address options are accepted, but no filter is applied.
  • The source does not auto-detect interfaces reliably; always set type=openbsdwifi.
  • The interface MAC address is changed when the source opens, and the source UUID is generated from it, so the UUID changes each time the source opens. Set a fixed UUID with the uuid= option if needed.