%PM-4-ERR_DISABLE
Port shut itself off (err-disabled): link-flap
The switch saw the link on this port drop and come back 5 times within 10 seconds (the default flap setting) and shut the port down on purpose to protect the network.
Troubleshoot › Error Decoder
Paste the exact line your device printed — or just its code, like %PM-4-ERR_DISABLE — and get the plain-English meaning, the likely causes in order, the commands to run, and the fix. Every entry is written from vendor documentation; an entry earns a "Verified in lab" label only after the fault has been reproduced and the fix proven in a Packet Path lab.
Port shut itself off (err-disabled): link-flap
The switch saw the link on this port drop and come back 5 times within 10 seconds (the default flap setting) and shut the port down on purpose to protect the network.
Port security violation: port shut down
The port is configured to allow only certain MAC addresses (the hardware addresses of approved devices).
BGP neighbor went down (or came up)
A BGP session — the connection that exchanges routes with a neighboring network — dropped.
OSPF neighbor dropped
Two routers that were exchanging routes with OSPF stopped hearing from each other.
Interface went down (and its line protocol followed)
The physical link on this port dropped.
Duplex mismatch between two connected devices
The two ends of one cable disagree about how to talk.
Native VLAN mismatch on a trunk
A trunk is a link carrying many VLANs (separate virtual networks) between switches.
Spanning tree blocked a port: VLAN inconsistency
Spanning tree — the safety system that prevents network loops — detected that this port's VLAN setup contradicts what is arriving on it, and blocked the port to protect the network.
UDLD shut the port: one-way link detected
UDLD is a watchdog that checks a link works in BOTH directions.
Duplicate IP address on the network
Two devices are claiming the same IP address.
EtherChannel refused: ports do not match
Several physical links can be bundled into one logical link (an EtherChannel / port-channel) — but only if every port in the bundle is configured identically.
HSRP router keeps changing role
HSRP pairs two routers so devices see one 'virtual' gateway; one router is Active (working) and the other is Standby (waiting).
IPsec VPN received a packet it cannot place
A VPN tunnel received an encrypted packet stamped with a security ID (SPI) that this router no longer knows.
Loop Guard blocked a port: possible one-way trouble
Loop Guard is a spanning-tree safety net.
BPDU Guard shut the port: something switch-like appeared on an access port
BPDU Guard is a tripwire on ports meant for end devices — PCs, phones, printers.
Loop-back detected: the switch heard its own voice come back
The switch sends itself small keepalive frames on every port.