003 - STP GUARD & FILTER

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Spanning Tree protection

BPDU Guard

• Prevent loops if another switch is attached to Portfast port
• When enabled on interface port goes in error-disabled state if BPDU is received

Switch (config-if)#spanning-tree bpduguard enable (note portfast may not be configured)

• Can be enabled on global configuration mode

Switch(config)#spanning-tree portfast bpduguard default

BPDU Filter:

· If enabled on interface mode it prevents the port from sending or receiving BPDU Switch(cofig-if)#spanning-tree bpdufilter enable

· If enabled globally if portfast interface receive the BPDU it take out portfast status Switch(config)#spanning-treee portfast bpdufilter default

Root Guard

• Prevent other switch becoming root bridge
• Enabled on ports other than the root port and on the switches other than root switch
• Root guard port receives a BPDU that might cause it to become a root port, then the port is put into “root inconsistent” state and does not pass traffic through it.
• But if port stops receiving these BPDU, it automatically re-enables itself Switch(config)#spanning-tree guard root.