While the 802.11 standard clearly defines two major ways in which a radio card can operate, an access point (AP) radio and a client station radio can be configured in a number of ways. The default configuration of an AP is to allow it to operate inside a basic service set (BSS); however, an AP can be configured to function in a nonstandard topology.

Client stations can be configured to participate in either a BBS or IBSS 802.11 service set. We will look at these two methods in the following.

Access Point Modes

The only configuration mode of an access point that is compliant with the 802.11 standard is known as root mode. The main purpose of an AP is to serve as a portal to a distribution system. The normal default setting of an access point is root mode, which allows the AP to transfer data back and forth between the DS and the 802.11 wireless medium.

The default root configuration of an AP allows it to operate as part of a basic service set (BSS). There are, however, other nonstandard modes in which an AP may be configured.

• Bridge mode The AP is converted into a wireless bridge.
• Workgroup Bridge mode The AP is transformed into a workgroup bridge.
• Repeater mode The AP performs as a repeater access point.
• Scanner mode The access point radio is converted into a sensor radio allowing the access point to integrate into a wireless intrusion detection system (WIDS) architecture.

Because these configurations are all considered nonstandard, not all vendors support these modes.

Client Station Modes

A client station may operate in one of two settings. The default mode for a client radio card is typically Infrastructure mode. When running in Infrastructure mode, the client station will allow communication via an access point. Infrastructure mode allows for a client station to participate in a basic service set or an extended service set.

Clients that are configured in this mode may communicate, via the AP, with other wireless client stations within a BSS. Clients may also communicate through the AP with other networking devices that exist on the distribution system, such as servers or wired desktops.

The second client station mode is called Ad-Hoc mode. Other vendors may refer to this mode as Peer-to-Peer mode. Client cards set to Ad-Hoc mode participate in an independent basic service set (IBSS) topology and do not communicate via an access point. All station transmissions and frame exchanges are peer-to-peer.