BPDU
Bridge Protocol Data Unit
Spanning Tree Protocol messages; BPDU Guard protects against rogue switches.
A BPDU is the message switches exchange to run Spanning Tree Protocol, sharing topology information so the network can build a loop-free path and avoid broadcast storms. Because a malicious or misconfigured device injecting BPDUs can force a recalculation and seize the root role, switches offer protections such as BPDU Guard, which disables an access port that unexpectedly receives one, and Root Guard. On the exam, link BPDU to Layer 2 availability threats and recognize these guard features as the standard mitigations against rogue switches.
Looking BPDU up is step one. Getting tested on it is step two.
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