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Notice in this example once again

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that BPDU Guard is enabled globally for Portfast ports on the switch, we type the command spanning tree,

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portfast, edge, BPDU Gaurd default.

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So if a portfast port receives a BPDU it will be shut down.

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So as an example show interface gigabit 01, this port is currently up.

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It is not configured as a portfast port.

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If that port was configured as a portfast port

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and we receive a BPDU on that port the port is shut down.

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So as soon as we typed the command and a BPDU was received the port was disabled, get rid of spanning tree

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portfast, shut the port down, no shut the port, the port will come up again show spanning tree.

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The port is up but it's in the blocking state.

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So it's been blocked by spanning tree but the port is up up. On switch 2 however, we configured BPDU guard

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directly on the port, the port is error disabled even though Portfast wasn't configured so soon as

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spanning tree, BPDU Guard is enabled on the port, the port goes error disabled when a BPDU is received. I'll remove

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that command from the port, shut it down and no shut it port comes up.

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So do show interface gigabit 02,

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currently the port is up up as soon as I enable BPDU Guard.

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We should see that the port goes error disable and there you go.

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Port is error disabled because the BPDU was received on the switch.

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So it's quite clear through the output to see that the port was shut down because of BPDU Guard.

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Once again if I remove that the port doesn't come up again.

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You have to shut the port down and then no shut it to re-enable the port so show interface gigabit 02

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port is currently up up, show spanning tree port is in the blocking state because it's a backup port

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in this network.

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So once again if you enable portfast on your switches ensure that you enable BPDU guard as an extra

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protection mechanism.