D-Link DES-3250TG User Manual page 171

D-Link DES-3250TG Standalone Layer 2 Switch
The priority for most cases is to restore connectivity as soon as possible. The simplest remedy is to manually disable all of the
ports that provide redundant links. Disabling ports one at a time, and then checking for a restoration of the user's connectivity
will identify the link that is causing the problem, if time allows. Connectivity will be restored immediately after disabling a
data loop.
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