Why does the AR router interface change between Up and Down

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When auto-negotiation is enabled on one end but disabled on the other end, set the same auto-negotiation mode on both ends. If auto-negotiation is enabled on one end of an electrical interface but disabled on the other end, packets may be discarded even when the interface is Up.

Other related questions:
There is a delay when a fixed switch interface alternates between Up and Down consecutively. Why
To prevent the interface from frequently reporting the status change event, run the carrier { up-hold-time | down-hold-time } interval command to set the delay in reporting the status change event. By default, the delay in reporting a port Up event is 2000 milliseconds, and the delay in reporting a port Down event is 0 milliseconds.

The state of an E1 interface is not Up when the interface interconnects with the peer device
For the problem that the state of an E1 interface of an AR router is not Up when the interface interconnects with other devices, see the troubleshooting guide. For details, access the URL in the right column.

The PPPoE physical interface is Up but the state of the protocol is Down
After a PPPoE dialup, all services are born on the Dialer interface, with corresponding physical interface being Up and protocol being Down, which is normal and does not affect the services and use. Ignore it. A virtual interface is needed for PPPoE dialup to bear all services. Pay attention to the Dialer interface, and the protocol status does not need to be concerned with.

The physical state of a serial interface is Up but the protocol state of the interface is Down
For the problem that the physical state of a serial interface is Up but the protocol state of the interface is Down, see the troubleshooting guide. For details, access the URL in the right column.

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