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The wireless client cannot associate to the access point

Core Issue

The wireless client cannot associate to the closest access point (AP), but it can associate to another one.

Resolution

The physical proximity of the device alone does not decide the association of the AP to the clients. These are some of the most common reasons:

  • A mismatch occurred in the service set identifier (SSID) and Authentication.
       
  • A mismatch occurred in the frequency between the AP and the client. If the APs in question are in same frequency [2.4 GHz band], make sure the client card is set to automatic frequency selection.

   

  • The data rates on the devices should match on the devices that communicate.

   

  • The Power Output of the nearby antenna is possibly be low. Check for the transmission power.   

Refer to Configuring Radio Settings for more information on how to configure Access Point 1200. This section explains the process of client roaming:

If there are multiple APs in your wireless topology, the client maintains an association with the AP that it originally associated with until it loses keepalive beacons from that AP.

If contact is lost, and the attempts to regain contact with the original AP continue to fail, the client then seeks out another AP. The client attempts to associate to it, provided that it has sufficient rights and authorization on the new AP.

If the client successfully associates to a second AP, it retains the new association.

A previously described roaming decision was associated with the detection of transmission problems by the client. But even if there is no transmission problem, the client can still roam to a better AP if it discovers one. This is because the client performs periodic scans for a better AP. This behavior is configurable in the latest versions of the Aironet Client Utility (ACU) that support Cisco Aironet 350 series client adapters and is not configurable for other Cisco clients.

Roaming is always a client station decision. The client station is responsible for detecting, evaluating, and roaming to an alternative access point. These are the sequence of events that occur when a client roams from Access Point A to Access Point B.

  1. A client moves from access point A coverage area into access point B coverage area, with both access points in the same subnet. As the client moves out of the range of access point A, a roaming event, for example, maximum retries, is triggered.

  2. The client scans all IEEE 802.11 channels for alternative access points. In this case, the client discovers access point B and reauthenticates and reassociates to it. After it is associated to the new access point B, if it is configured for 802.1X, the client begins IEEE 802.1X authentication.

  3. Access point B sends a null media access control (MAC) multicast, on the virtual local area network (VLAN), with the source address of the client. This updates the content addressable memory (CAM) tables of the upstream switch and directs further LAN traffic for the client to access point B and not access point A.

  4. With its own source address, access point B sends a MAC multicast, on the native VLAN, and tells access point A that access point B now has the client associated to it. Access point A receives this multicast and removes the client MAC address from its association table.

In order to keep roaming under control, you should conduct a proper site survey. It is also helpful if all the APs within a wireless LAN are kept at a certain transmit level. Clients roam if they are out of a cell range or they do not receive or send any beacon frames from the associated AP. You should have a 15-20 percent overlap of radio cell when APs are set up for roaming clients.