---
name: "an"
section: "4"
platform: "openbsd"
package: "man"
version: "8.0-current-20261101"
release: "OpenBSD 8.0-current (2026-11-01)"
platforms: ["linux", "openbsd"]
url: "https://new.carta.tech/an/4"
---

# an(4)

Aironet Communications 4500/4800 IEEE 802.11FH/b wireless network device

## NAME

**an** – Aironet Communications 4500/4800 IEEE 802.11FH/b wireless network device

## SYNOPSIS

**an\* at pcmcia?** **an\* at pci?** **an\* at isapnp?**

## DESCRIPTION

The **an** driver provides support for the Aironet Communications 4500, 4800 (aka Cisco 340), and Cisco 350 IEEE 802.11 wireless network adapters. This includes the ISA, PCI, and PCMCIA varieties. The 4500 series adapters operate at 1 and 2Mbps (FH) while the 4800 and 350 series can operate at 1, 2, 5.5, and 11Mbps (DS). The ISA, PCI, and PCMCIA devices are all based on the same core PCMCIA modules and all have the same programming interface. However, unlike the Lucent WaveLAN/IEEE cards, the ISA and PCI cards appear to the host as normal ISA and PCI devices and do not require any PCMCIA support.

ISA cards can either be configured to use ISA Plug and Play or to use a particular I/O address and IRQ by properly setting the DIP switches on the board. (The default switch setting is for plug and play.) The **an** driver has Plug and Play support and will work in either configuration, however when using a hard-wired I/O address and IRQ, the driver configuration and the NIC's switch settings must agree. PCI cards require no switch settings of any kind and will be automatically probed and attached.

All host/device interaction with the Aironet cards is via programmed I/O. The **an** driver encapsulates all IP and ARP traffic as 802.11 frames, though it can receive either 802.11 or 802.3 frames.

These are the modes the **an** driver can operate in:

- BSS mode

  Also known as *infrastructure* mode, this is used when associating with an access point, through which all traffic passes. This mode is the default.

- IBSS mode

  Also known as *IEEE* *ad-hoc* mode or *peer-to-peer* mode. This is the standardized method of operating without an access point. Stations associate with a service set. However, actual connections between stations are peer-to-peer.

- monitor mode

  In this mode the driver is able to receive packets without associating with an access point. This disables the internal receive filter and enables the card to capture packets from networks which it wouldn't normally have access to, or to scan for access points.

The **an** driver can be configured to use hardware Wired Equivalent Privacy (WEP). It is strongly recommended that WEP not be used as the sole mechanism to secure wireless communication, due to serious weaknesses in it.

In BSS mode, the driver supports powersave mode, which can be enabled via [ifconfig(8)](/ifconfig/8.md).

The **an** driver can be configured at runtime with [ifconfig(8)](/ifconfig/8.md) or on boot with [hostname.if(5)](/hostname.if/5.md).

## EXAMPLES

The following [hostname.if(5)](/hostname.if/5.md) example configures an0 to join network “mynwid”, using WEP key “mywepkey”, obtaining an IP address using DHCP:

```
join mynwid nwkey mywepkey
inet autoconf
```

## DIAGNOSTICS

- an0: failed to allocate N bytes on NIC

  The driver was unable to allocate memory for transmit frames in the NIC's on-board RAM.

- an0: device timeout

  The Aironet card failed to generate an interrupt to acknowledge a transmit command.

## SEE ALSO

[arp(4)](/arp/4.md), [ifmedia(4)](/ifmedia/4.md), [intro(4)](/intro/4.md), [isapnp(4)](/isapnp/4.md), [netintro(4)](/netintro/4.md), [pci(4)](/pci/4.md), [pcmcia(4)](/pcmcia/4.md), [hostname.if(5)](/hostname.if/5.md), [ifconfig(8)](/ifconfig/8.md)

## HISTORY

The **an** device driver first appeared in FreeBSD 4.0. OpenBSD support was added in OpenBSD 2.7. A version of the driver based on the one in NetBSD was added in OpenBSD 3.9.

## AUTHORS

The **an** driver was written by Bill Paul ⟨*wpaul@ee.columbia.edu*⟩ and ported to OpenBSD by Michael Shalayeff ⟨*mickey@openbsd.org*⟩. Later the NetBSD version of the driver by Atsushi Onoe was subsequently ported to OpenBSD by Jonathan Gray ⟨*jsg@openbsd.org*⟩.

## CAVEATS

Scanning for access points is not currently supported.