One Portfast network failure on Cisco

Reason: The company panel interface is not enough, through the small Fool switch expansion interface .

phenomenon: Small fool switch Connection panel, then computer connection small fool switch. Found that the computers are not ping gateway, but can ping each other . Description Small fool switch is no problem, the connection between the small fool switch and the original switch fails .

View the original switch configuration and find the Portfast configured . and Spanning-tree Bpduguard enable is behind it.

Find the data where the problem lies:

will be SWITCH the port is set to Spanning-tree Portfast after the

If this port is connected to another SWITCH or HUB may cause loop problems.

Plus spanning-tree Bpduguard Enable after that, when the port is receiving BPDUs The bag will go into errdisable . Status , thus avoiding loops.

that when the switch port is set to fast port, the switch or hub is not normally connected . The fast port is also intended to connect to the host or server .

so with the command spanning-tree Bpduguard enable, when the port receives a BPDU packet, it enters the errdisable state, thus avoiding the loop.

therefore, when the Panel interface in the network is not sufficient to use the switch expansion, you need to carefully check the original switch port. See if there is a quick port configured , whether there is a spanning-tree bpduguard enable this command .

Otherwise, when you expand the interface via the switch, the corresponding switch port will be down .

One Portfast network failure on Cisco