Improperly shielded microwave ovens♦
Wireless equipment that other companies manufacture♦
Electrical motors and the moving metal parts of machinery can also cause interference. Refer
to these documents for more information:
Troubleshooting Problems Affecting Radio Frequency Communication♦
Intermittent Connectivity Issues in Wireless Bridges♦
Q. I see the error message : %C4K_EBM−4−HOSTFLAPPING:Host
[mac−addr] in vlan [num] is flapping between port [num] and port [num]
connected to the Access Points. How do we resolve this?
A. This error message occurs when switch learns the same MAC address through multiple
ports. This can be due to one of these reasons
When a client roams from one AP to another AP, the new AP informs the client of
the MAC address to the switch. If both the APs are connected to the same switch, the
MAC address of the client is associated to both the switch ports connected to the APs.
This creates a duplicate entry for the client and generates this error message until the
time that the switch synchronizes its CAM table. This error message is quite normal
in a wireless environment, but, if too much roaming occurs, this can overload the
CPU of the switch. Check the client driver and firmware. In addition, ensure that
coverage is good so that the client does not roam often.
1.
When there is a loop, the switch can learn the same MAC address through multiple
ports connected to other switches. Ensure that the TP is enabled on the switch.
2.
Q. Why is it that the client card does not associate to the closest AP?
A. If there are multiple APs in your wireless topology, your client maintains an association
with the AP with which the client originally associated, until the client loses keepalive
beacons from that AP. If contact is lost and if attempts to regain contact with the original AP
continue to fail, the client then seeks out another AP. The client attempts to associate to this
new AP if the client has sufficient rights and authorization on the new AP.
Q. I have a Cisco AP and Cisco Secure Access Control Server (ACS) 3.2.
I have Extensible Authentication Protocol (EAP) implemented in the
network. Users are not authenticated by the RADIUS server. When I
issue debug commands on the AP, I get this output: "Jun 2
15:58:13.553: %RADIUS−4−RADIUS_DEAD: RADIUS server
10.10.1.172:1645,1646 is not responding. Jun 2
15:58:13.553: %RADIUS−4−RADIUS_ALIVE: RADIUS server
10.10.1.172:1645,1646 has returned. Jun 2 15:58:23.664:
%DOT11−7−AUTH_FAILED: Station 0040.96a0.3758
Authentication failed." Why do I see these error messages on the
AP?
A. One of the reasons why these error messages appear is that the shared secret is not the
same in the AP and the ACS. This mistake is common when you configure EAP. If there is a
shared−secret mismatch between the AP and the ACS 3.2, EAP does not work. The RADIUS
server does not accept packets that the AP forwards. Ensure that the shared secret on the AP
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