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Cisco Switch 發生Loopback

User告知網路無法使用，看了Switch的狀況後，發現那個Port的狀態是Error Disable，接著又看了Switch的log


Feb  8 12:14:14 TW: %DHCP_SNOOPING-5-DHCP_SNOOPING_UNTRUSTED_PORT: DHCP_SNOOPING drop message on untrusted port, message type: DHCPNAK, MAC sa: 2c56.dc86.xxxx
Feb  8 12:15:49 TW: %DHCP_SNOOPING-5-DHCP_SNOOPING_UNTRUSTED_PORT: DHCP_SNOOPING drop message on untrusted port, message type: DHCPNAK, MAC sa: 2c56.dc86.xxxx
Feb  8 12:18:00 TW: %ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected on FastEthernet0/10.
Feb  8 12:18:00 TW: %PM-4-ERR_DISABLE: loopback error detected on Fa0/10, putting Fa0/10 in err-disable state
Feb  8 12:18:01 TW: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/10, changed state to down
Feb  8 12:18:02 TW: %LINK-3-UPDOWN: Interface FastEthernet0/10, changed state to down


應該是User私接設備，除了造成Loopback之外，又在隨便發放IP.......

不過因為那個User比較特殊，先教育了一下之後，再把那個Port shutdown , no shutdown，接著把Recovery設了上去，下次如果再遇到相同狀況，10分鐘後會自動恢復

xxxxx#show errdisable detect
ErrDisable Reason    Detection status
-----------------    ----------------
udld                 Enabled
bpduguard            Enabled
security-violatio    Enabled
channel-misconfig    Enabled
psecure-violation    Enabled
dhcp-rate-limit      Enabled
unicast-flood        Enabled
vmps                 Enabled
pagp-flap            Enabled
dtp-flap             Enabled
link-flap            Enabled
gbic-invalid         Enabled
loopback             Enabled


xxxxx(config)#errdisable recovery cause loopback
xxxxx(config)#errdisable recovery interval 600


xxxxx#show errdisable recovery
ErrDisable Reason    Timer Status
-----------------    --------------
udld                 Disabled
bpduguard            Disabled
security-violatio    Disabled
channel-misconfig    Disabled
vmps                 Disabled
pagp-flap            Disabled
dtp-flap             Disabled
link-flap            Disabled
psecure-violation    Disabled
gbic-invalid         Disabled
dhcp-rate-limit      Disabled
unicast-flood        Disabled
loopback             Enabled

Timer interval: 600 seconds

Interfaces that will be enabled at the next timeout:



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