Other STP Enhancement Features

The remainder of this chapter focuses on other enhancements that Cisco has included in its IOS switches to help with STP issues. These features include BPDU skewing, Root Guard, Unidirectional Link Detection, Loop Guard, and some additional troubleshooting tips and tools to assist you in scaling STP to a large number of switches.

BPDU Skewing

BPDU skewing refers to the time differential between when BPDUs are expected to be received by a switch and when they are actually received. BPDU skewing can occur in any of the following situations:

  • STP topology changes occur

  • One of STP's timers expires

  • A BPDU is not received within the expected time interval

When any of these three occurrences happens, switches flood the network ...

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