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AP1200 causes spanning-tree 'Alt BLK'


Can you help please?

I have four 1200's covering an area, with some radio overlap.

One of the AP's is causing it's switch-port to go into spanning-tree "Altn BLK" state constantly.

The AP's are running an more or less 'out-of-the-box' configuration.

The switchport config is here:


interface GigabitEthernet2/0/22

switchport access vlan 60

switchport mode access


What is causing this, and how can I stop it?

Thanks in advance,

  • Other Network Infrastructure Subjects

Re: AP1200 causes spanning-tree 'Alt BLK'

Most likely cause is that the switchport is receiving BPDU's via the AP, making it think there is a loop in the network. Is the Access Point the only device on this port?

If not, I suggest that you try and disconnect the AP to check if the port goes back to forwarding mode.

If the access points are in bridge-mode the loop may be caused by the radio overlap. You should reconfigure your access points for this. The best way to do this is to configure them on different radio channels. Preferrably use channel 1, 6 and 11 and then once more channel 1. Make sure that both AP's on channel 1 do not overlap.



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