Broadcast Storms - Loop Prevention

Broadcast Revisited

• If the destination is the broadcast MAC FF-FF-FF-FF-FF-FF OR if the destination is an unknown unicast
  • Switch sends the frame out all ports except the one it came on
• Not problematic in a simple topology

Broadcast Storms

• In a more advanced environment broadcast can become problematic
  • You can't always think of Spanning Tree running (Cisco does)
• Goals: redundancy / better paths
• No TTL at Layer 2
  • No Time To Live
• Cause instability to the MAC table
• Links saturated
• Solution: block on redundant links

• Spanning Tree Protocol (STP)
  • Announcing theirselves and figuring out who their neighbors are
  • Who is gonna be the boss?
    • Has the lowest priority
    • The lowest MAC address
      • 48 bits
      • First 24 are your organizations identifiers
      • Maybe the oldest device in the network