interface Gi [X/X/X]

1. Фаст порт-секьюрити (ФПС)

1.1 Проверяем конфиг порта.

> show running-config interface Gi [X/X/X]

1.2 Самый плохой сценарий

Видим либо пустой конфиг порта в 2 строки. Либо пример ниже.

interface GigabitEthernet [X/X/X]
 switchport mode access
 switchport access vlan 2
 switchport port-security
 switchport port-security violation shutdown
 switchport port-security maximum 8
 switchport port-security mac-address sticky
 switchport port-security mac-address sticky xxxx.xxxx.xxxx
 switchport port-security mac-address sticky yyyy.yyyy.yyyy
 switchport port-security mac-address sticky cccc.cccc.cccc
 switchport port-security mac-address sticky zzzz.zzzz.zzzz
 switchport port-security mac-address sticky aaaa.aaaa.aaaa
 switchport port-security mac-address sticky bbbb.bbbb.bbbb
 switchport port-security mac-address sticky dddd.dddd.dddd
 switchport port-security mac-address sticky eeee.eeee.eeee
 spanning-tree portfast
 ... и так далее

1.3 Быстро лечим порт

> configure terminal

(config-if)#