CCIE RS – Written – L2 – Describe Spanning-Tree Concepts

CCIE RS – Written – L2 – Describe Spanning-Tree Concepts


Compatibility between MST and RSTP

Talked about in the earlier blog post on STP

Common Spanning Tree

  • Interconnecting different MST regions and non-MST
  • Common Instance Spanning-Tree (CIST)
  • Single spanning tree that spans entire switch topology
    • Can have multiple root switches
    • CIST Root – One for entire CIST
    • CIST Regional Root – one per IST inside of each region

STP Dispute

Checks consistency of port role and state in the received BPDU to detect unidirectional links that could cause L2 loops

  • Moves port to discarding state


STP Bridge Assurance

6500 switch optional feature – Enabled by default

  • Supported only by RPVST+ and MST
  • Both ends must have Bridge Assurance enabled
  • Runs only on P2P STP ports
  • BPDU’s are sent out all operational network ports each hello period
    • Including alternate and backup ports

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/12-2SX/configuration/guide/book/stp_enha.html

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