Portfast, BPDU Filter and BPDU Guard

Not how other people learned SPT. When I was learning (still learning actually), I got lost among the features, protection mechanisms. Here below are just some of the tons.

PortFast:

1. Enabled Globally:
If portfast is enabled globally, all access ports will start forwarding traffic immediately unless BPDU is received. The ports will loss port fast and go through all STP states to become forwarding.

2. Enabled Per Port:
If portfast is enabled on specific switch port, no matter BPDU is received or not on the port, portfast will stay.

BPDU Filter:

1. Enabled Globally:
If BPDU Filter is configured as part of global “portfast” configuration, it will be used to prevent switch sending BPDU frame on “portfast” ports. However if another switch is also connected to the “portfast” port, in order for 2 switches to identify each other as switches not hosts, there will be “couple of BPDU” sent when port initially become active.

2. Enabled Per Port:
If BPDU Filter is enabled per switch port, the port will never send BPDU frame out.

BPDU Guard:

1. Enabled Globally:
If BPDU Guard is enabled globally, ALL the “portfast” ports will be disabled (err-disable) if there is BPDU received.

2. Enabled Per Port:
If BPDU Guard is enabled per switch port, that “portfast” port will be disabled (err-diable) if there is BPDU received on it.

NOTES:
1. When BPDU Filter or BPDU Guard is enabled on a specific port, the feature will work no matter port fast is configured or not.

2. If BPDU Filter and BPDU Guard are both configured on a port, BPDU filter takes precedence.

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