What the differences between BPDU guard and BPDU filter?

BPDU Guard and BPDU Filter are related but distinct features designed to protect a network from unauthorized switches or devices that could cause spanning tree protocol (STP) issues. Let's clarify the differences between these two mechanisms:
BPDU Guard

Purpose: BPDU Guard is a security feature that prevents unauthorized switches or devices from becoming part of the spanning tree topology.
HowIt Works: When enabled on a port, BPDU Guard monitors the incoming Bridge Protocol Data Units (BPDUs). If a BPDU is received on a port where BPDU Guard is enabled and the port is in a designated or root port state, the port is immediately put into an error-disabled state.
Behavior: The port remains in the error-disabled state until manually reset by an administrator. This prevents loops and ensures that only authorized devices can participate in the spanning tree.
BPDU Filter

Purpose: BPDU Filter is a mechanism that blocks the transmission of BPDUs out of aspecific port.
HowIt Works: When BPDU Filter is enabled on a port, the switch stops sending BPDUsout of that port. However, the port continues to receive BPDUs.
Behavior: This feature is useful for protecting a port from receiving unwanted BPDUs,which could cause the port to become a root port and potentially create a loop.Unlike BPDU Guard, BPDU Filter does not disable the port; it simply preventsthe port from sending BPDUs.
Summary

BPDU Guard:
￮ Monitors and blocks incoming BPDUs on a port.
￮ Disables the port if a BPDU is received.
￮ Prevents unauthorized switches from participating in the spanning tree.
BPDU Filter:
￮ Blocks outgoing BPDUs from a port.
￮ Allows the port to continue receiving BPDUs.
￮ Helps to prevent loops by avoiding the port from becoming a root port.
Comparison

While both BPDU Guard and BPDU Filter are designedto enhance network security and prevent loops, they operate differently:
• BPDU Guard is more aggressive, disabling the port upon detection of an incoming BPDU.
• BPDU Filter is less disruptive, as it only blocks outgoing BPDUs and allows the portto remain operational.
In summary, BPDU Guard and BPDU Filter serve different purposes and should be used according to the specific needs of your network. If you want to completely prevent unauthorized devices from participating in the spanning tree, you would use BPDU Guard. If you want to prevent loops without disabling the port, you should use BPDU Filter.