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STP

Torsten Rehn
November 09, 2016

 STP

Spanning Tree Protocol

Torsten Rehn

November 09, 2016
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  1. STP P A
 N N I
 N
 G
 R
 O

    T O C O L
 R E E

  2. S S S PC PC To: To: To: To: To:

    To: To: To: To: To: To: To:
  3. Designate a root For each switch, find the shortest path

    to the root For each cable, determine which end has the shorter path to root On each switch, disable all other ports that lead to root
  4. Designate a root For each switch, find the shortest path

    to the root For each cable, determine which end has the shorter path to root On each switch, disable all other ports that lead to root ✓
  5. Protocol ID Version Type Flags Root ID Path cost Bridge

    ID Port ID Age Max Age Hello Fwd Delay 2 B 1 B 1B 1 B 8 B 4 B 8 B 2 B 2 B 2 B 2 B 2 B always zero (for classic STP)
  6. Protocol ID Version Type Flags Root ID Path cost Bridge

    ID Port ID Age Max Age Hello Fwd Delay 2 B 1 B 1B 1 B 8 B 4 B 8 B 2 B 2 B 2 B 2 B 2 B config topology change topology change ack
  7. Protocol ID Version Type Flags Root ID Path cost Bridge

    ID Port ID Age Max Age Hello Fwd Delay 2 B 1 B 1B 1 B 8 B 4 B 8 B 2 B 2 B 2 B 2 B 2 B 2 B priority + 6 B MAC address
  8. Protocol ID Version Type Flags Root ID Path cost Bridge

    ID Port ID Age Max Age Hello Fwd Delay 2 B 1 B 1B 1 B 8 B 4 B 8 B 2 B 2 B 2 B 2 B 2 B total “cost” to root 100 MBit/s: 200k 1 GBit/s: 20k
  9. Protocol ID Version Type Flags Root ID Path cost Bridge

    ID Port ID Age Max Age Hello Fwd Delay 2 B 1 B 1B 1 B 8 B 4 B 8 B 2 B 2 B 2 B 2 B 2 B 2 B priority + 6 B MAC address
  10. Protocol ID Version Type Flags Root ID Path cost Bridge

    ID Port ID Age Max Age Hello Fwd Delay 2 B 1 B 1B 1 B 8 B 4 B 8 B 2 B 2 B 2 B 2 B 2 B physical port of sender
  11. Protocol ID Version Type Flags Root ID Path cost Bridge

    ID Port ID Age Max Age Hello Fwd Delay 2 B 1 B 1B 1 B 8 B 4 B 8 B 2 B 2 B 2 B 2 B 2 B hops since initial BPDU from root
  12. Protocol ID Version Type Flags Root ID Path cost Bridge

    ID Port ID Age Max Age Hello Fwd Delay 2 B 1 B 1B 1 B 8 B 4 B 8 B 2 B 2 B 2 B 2 B 2 B max TTL
  13. Protocol ID Version Type Flags Root ID Path cost Bridge

    ID Port ID Age Max Age Hello Fwd Delay 2 B 1 B 1B 1 B 8 B 4 B 8 B 2 B 2 B 2 B 2 B 2 B interval between periodic config BPDUs
  14. Protocol ID Version Type Flags Root ID Path cost Bridge

    ID Port ID Age Max Age Hello Fwd Delay 2 B 1 B 1B 1 B 8 B 4 B 8 B 2 B 2 B 2 B 2 B 2 B time spent learning/listening
  15. Designate a root For each switch, find the shortest path

    to the root For each cable, determine which end has the shorter path to root On each switch, disable all other ports that lead to root ✓ ✓ ✓ ✓
  16. RSTP PORT STATES DISCARDING Only BPDUs are transmitted. LEARNING Like

    DISCARDING, but learns MAC addresses. FORWARDING Regular data is transmitted.
  17. RSTP PORT ROLES ROOT Best path to root bridge. DESIGNATED

    Points away from root. ALTERNATE Worse (and thus disabled) path to root bridge. BACKUP Leads to same segment as another DESIGNATED port.
  18. Designate a root For each switch, find the shortest path

    to the root For each cable, determine which end has the shorter path to root On each switch, disable all other ports that lead to root
  19. S S S S 2 3 8 9 20,000 20,010

    10,000 10,000 root bridge
  20. Designate a root For each switch, find the shortest path

    to the root For each cable, determine which end has the shorter path to root On each switch, disable all other ports that lead to root
  21. S S S S 2 3 8 9 20,000 20,010

    10,000 10,000 root bridge R R R
  22. Designate a root For each switch, find the shortest path

    to the root For each cable, determine which end has the shorter path to root On each switch, disable all other ports that lead to root
  23. S S S S 2 3 8 9 20,000 20,010

    10,000 10,000 root bridge R R R D D D D
  24. Designate a root For each switch, find the shortest path

    to the root For each cable, determine which end has the shorter path to root On each switch, disable all other ports that lead to root
  25. S S S S 2 3 8 9 20,000 20,010

    10,000 10,000 root bridge R R R D D D D A
  26. S S S S 2 3 8 9 20,000 20,010

    10,000 10,000 root bridge R R R D D D D A port discarding