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Topology Change Notifications (TCN)

What exactly triggers a switch to send a TCN to the root switch? Connecting/disconnecting from a host or another switch? A CAM entry times-out and then the device reappears causing a new entry to be created? Others? Thanks.

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Cisco Employee

Re: Topology Change Notifications (TCN)

Basically any event which leads a port transitioning to or from the forwarding state will generate TCNs. You can configure portfast on ports connecting to hosts and this will avoid TCN generation since the port would go to forwarding directly. The following tech tips should help

http://www.cisco.com/warp/public/473/17.html

http://www.cisco.com/warp/public/473/143.html#cause2

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