>STP - какой у тебя? Лучаем не MSTP? Manager AT-9924SP> show stp summ
STP Name Mode Ports Enabled Ports Disabled Bridge Role
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default Standard 0 24 Root Bridge
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Manager AT-9924SP> show mstp
MSTP Information
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MSTP status .................................. Disabled
MST Configuration Name ....................... 00-00-cd-23-db-5f
Revision Level ............................... 0
Number of MSTIs .............................. 0
Hello Time ................................... 2
Forward Delay ................................ 15
Message Max Age .............................. 20
Max Hops ..................................... 20
Protocol Version ............................. MSTP
Support Static VLANs ......................... Disabled
Transmission Limit ........................... 3
Migrate Time ................................. 3
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Manager AT-9924SP>
MSTP вообще выключен ...