Turn: https://www.2cto.com/net/201303/198724.html
err-disable causes and solutions emerge switch
LOG Example:
21w6d: %ETHCNTR-3-LOOP_BACK_DETECTED: Keepalive packet loop-back detected on FastEthernet0/20.
21w6d: %PM-4-ERR_DISABLE: loopback error detected on Fa0/20, putting Fa0/20 in err-disable state
Information, the port is err-disabled state, and later with errdisable recovery cause loopback restored.
As more reason err-disable, it needs further confirmation, leading to a few common reasons err-disable the switch interface appears:
1. EtherChannel misconfiguration
2. Duplex mismatch
3. BPDU port guard
4. UDLD
5. Link-flap error
6. Loopback error
7. Port security violation
When both ends of the first F EC configuration mismatch occurs when err-disable. Suppose the FEC mode configuration Switch A is on, this time is not sent Switch A and Switch B PAgP packet negotiation connected to the FEC, it is assumed that Switch B has configured the FEC. However, the practical Swtich B and the FEC is not configured, when the state of the Switch B over 1 minute, STP Switch A would appear that there is a loop, so it appears err-disable. The solution is to FEC mode configuration is channel-group 1 mode desirable non-silent This means that only when the two sides after the FEC negotiated successfully established channel, otherwise the interface is still in the normal state.
The second reason is a mismatch duplex. After the end configured to half-duplex, he will detect whether the peer data transmission, only stop transmitting data to the end, he would like to send ack packet to make the link up, but to end it became a full-duplex configuration he do not care whether the link is idle, so that he would stop sending requests link up, so go on, the link state becomes the err-disable.
The third reason BPDU, and is related to BPDU guard and portfast. If an interface is configured portfast, that means that this interface should be connected to a pc, pc will not send BPDU frame spanning-tree is, so this port also receives BPDU to generate spanning-tree, the administrator is also out of good intentions on the same interface is configured with BPDU guard to prevent unknown BPDU frame to enhance security, but he just does not care to configure a switch receives this BPDU guard and portfast on the interface, so this interface received a BPDU frame, because the configuration the BPDU guard, this interface is natural to enter into err-disable state. Solution: no spanning-tree portfast bpduguard default, or directly to the portfast off.
The fourth reason is UDLD. 2 is a private UDLD cisco layer protocol for unidirectional link problem detection. Sometimes the physical layer is up but the link layer is down, this time you need UDLD to detect whether the link is really up. When the ends are configured UDLD AB, A sends B a frame containing its own port id UDLD after UDLD B receives a return frame, and which contains the A port id received, when A receives after this frame and the port id found himself among them, that this link is good. Conversely becomes a err-disable state. Suppose A is configured with UDLD, and B is not configured UDLD: A to B to send a frame containing its own port id after receipt of B does not know what the frame is that it does not return a UDLD frame contains the port id of A , this time a link would think this is a one-way link, naturally became the err-disable state.
The fifth reason is the link jitter, when the link up again within 10 seconds, down five times, then enter the err-disable state.
The sixth reason is keepalive loopback. Before 12.1EA, the switch sends keepalive default interface information at all, due to some unreasonable consultations spanning-tree switch may be a problem, but the interface has received a keepalive own issue, then this interface will become err- disable the. The solution is to put keepalive off. Or to ios rise 12.2SE.
The last reason is relatively simple, it is due to the configuration of the port-security violation shutdown.