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Updated:February 21, 2020
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Link flap is a situation in which a physical interface on the switch continually goes up and down, three or more times a second for duration of at least 10 seconds. The common cause is usually related to bad, unsupported, or non-standard cable or Small Form-Factor Pluggable (SFP), or related to other link synchronization issues. The cause for link flapping can be intermittent or permanent.
Link flap prevention mechanism minimizes the disruption to switch and network operation in a link flap situation. It stabilizes the network topology by automatically setting the ports that experience excessive link flap events to err-disable state ports. This mechanism also provides time to debug and locate root cause for flapping. A syslog message or Simple Network Management Protocol (SNMP) trap is sent to alert regarding link flap and port shutdown. The interface will become active again only if specifically enabled by the system administrator.
This article provides instructions on how to enable the Link Flap Prevention feature, configure Automatic ErrDisable Recovery settings, and reactivate a suspended interface through the Command Line Interface (CLI) of the switch.