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CCNP Switch 300-115 - STP - Part 2

The Spanning Tree Protocol (STP) is a network protocol that builds a loop-free logical topology for Ethernet networks. The basic function of STP is to prevent bridge loops and the broadcast radiation that results from them.

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CCNP Switch 300-115 - STP - Part 2

  1. 1. Campus Network with an Inefficient Root Bridge Election
  2. 2. Campus Network with STP Converged
  3. 3. Final Spanning-Tree Structure for the Campus Network
  4. 4. Key Topic 1. Manually setting the bridge priority value so that a switch is given a lower-thandefault bridge ID value to win a root bridge election. Switch(config)# spanning-tree vlan vlan-list priority bridge-priority 2. The bridge-priority value defaults to 32,768, but you can also assign a value of 0 to 65,535. 3. If STP extended system ID is enabled, the default bridge-priority is 32,768 plus the VLAN number. 4. In that case, the value can range from 0 to 61,440, but only as multiples of 4096. A lower bridge priority is preferable. 5. If you are not sure that your priority value will be accepted, enter it anyway. The switch will respond with a list of accepted values that are multiples of 4096: Switch(config)# spanning vlan 5,100-200 priority 4000 % Bridge Priority must be in increments of 4096. % Allowed values are: 0 4096 8192 12288 16384 20480 24576 28672 32768 36864 40960 45056 49152 53248 57344 61440 6. Use the primary keyword 6.1 Switch(config)# spanning-tree vlan vlan-id root { primary | secondary } 6.2. If the current root priority is more than 24,576, the local switch sets its priority to 24,576. 6.3. If the current root priority is less than that, the local switch sets its priority to 4096 less than the current root.
  5. 5. Default Spanning-Tree Configuration
  6. 6. Switch#show spanning-tree VLAN0001 Spanning tree enabled protocol ieee Root ID Priority 32769 Address 0060.2F92.8385 This bridge is the root Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 32769 (priority 32768 sys-id-ext 1) Address 0060.2F92.8385 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 20 Interface Role Sts Cost Prio.Nbr Type ---------------- ---- --- --------- -------- -------------------------------- Fa0/1 Desg FWD 19 128.1 P2p Fa0/2 Desg FWD 19 128.2 P2p VLAN0002 Spanning tree enabled protocol ieee Root ID Priority 24578 Address 0090.21E7.33E8 Cost 19 Port 2(FastEthernet0/2) Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Bridge ID Priority 28674 (priority 28672 sys-id-ext 2) Address 0060.2F92.8385 Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec Aging Time 20 Interface Role Sts Cost Prio.Nbr Type ---------------- ---- --- --------- -------- -------------------------------- Fa0/1 Altn BLK 19 128.1 P2p Fa0/2 Root FWD 19 128.2 P2p Instance 1 Instance 2
  7. 7. MAC1 < MAC2 < MAC3 PRIORITY = 32768 ------------------------------------------- Roles States ------------------------------------------- Root Port FWD Designated Port FWD Alternate Port BLK ------------------------------------------- STP Convergence
  8. 8. MAC1 < MAC2 < MAC3 PRIORITY = 32768 ConvergenceStateFWDBLK STATE. STP Convergence SW1(config)#interface gigabitEthernet 0/1 SW1(config-if)#shut
  9. 9. Change State ------------------------------------------------- Root Port (FW)  Alternate (BLK) Designated Port (FW)  Alternate (BLK) Change State ------------------------------------------------- Alternate  Root Port Alternate  Designated Port
  10. 10. STP Convergence 1 CONVERGENCENO CONVERGENCE
  11. 11. SW1(config)#interface g0/1 SW1(config-if)#shut SW1(config-if)#no shut :Show spanning-treeSW1GIG0/1 STP Convergence 2
  12. 12. STP Convergence 3 Interface Role Sts Cost Prio.Nbr Type ----------------------------------------------------------------------------- Fa0/1 Desg FWD 19 128.1 P2p Gi0/1 Desg FWD 4 128.25 P2p Interface Role Sts Cost Prio.Nbr Type ----------------------------------------------------------------------------- Fa0/1 Desg FWD 19 128.1 P2p Gi0/1 Desg LRN 4 128.25 P2p Interface Role Sts Cost Prio.Nbr Type ----------------------------------------------------------------------------- Fa0/1 Desg FWD 19 128.1 P2p Gi0/1 Desg LSN 4 128.25 P2p 15LSN . Forward Delay = 15 sec 15LRN . Forward Delay = 15 sec
  13. 13. SW1(config)#interface g0/1 SW1(config-if)#shut SW1SW2SW2RP TCN (Topology Change Notification) BPDU. STP Convergence 4
  14. 14. STP Convergence 5
  15. 15. SW1 SW2 SW2 Fa0/2Fa0/1 ROOT BRIDGE DPDP RP RP DP BLK Fa0/1 Fa0/3 Fa0/3 Fa0/2 STP Convergence 1 STP Topology Change Kind ------------------------------------------------------------- 1- Direct Topology Change 2- Indirect Topology Change 3- Insignificant Topology Change BLK  LSN(15s)  LRN(15s)  FWD BLK  FWD = 30 sec In Direct Topology Change What’s going on if this link fail?
  16. 16. SW1 SW2 SW2 Fa0/2Fa0/1 ROOT BRIDGE DPDP RP RP DP BLK Fa0/1 Fa0/3 Fa0/3 Fa0/2 STP Convergence 2 STP Topology Change Kind ------------------------------------------------------------- 1- Direct Topology Change 2- Indirect Topology Change 3- Insignificant Topology Change What’s going on if this link fail?
  17. 17. SW1 SW2 SW2 Fa0/2Fa0/1 ROOT BRIDGE DPDP RP RP DP BLK Fa0/1 Fa0/3 Fa0/3 Fa0/2 STP Convergence 3 2- Indirect Topology Change BID1 , BID2 , 4 , 128.3
  18. 18. SW1 SW2 SW2 Fa0/2Fa0/1 ROOT BRIDGE DPDP RP RP DP BLK Fa0/1 Fa0/3 Fa0/3 Fa0/2 STP Convergence 4 2- Indirect Topology Change BID2 , BID2 , 0 , 128.3 BLK  MAX-AGE-TIMER(20s)  LSN(15s)  LRN(15s)  FWD BLK  FWD = 50 sec Indirect Topology Change FAIL
  19. 19. SW1 SW2 SW2 Fa0/2Fa0/1 ROOT BRIDGE DPDP RP RP DP BLK Fa0/1 Fa0/3 Fa0/3 Fa0/2 STP Convergence 5 STP Topology Change Kind ------------------------------------------------------------- 1- Direct Topology Change 2- Indirect Topology Change 3- Insignificant Topology Change BLK  LSN(15s)  LRN(15s)  FWD BLK  FWD = 30 sec Insignificant Topology Change What’s going on when you connect a PC to switch?
  20. 20. SW1 SW2 SW2 Fa0/2Fa0/1 ROOT BRIDGE DPDP RP RP DP BLK Fa0/1 Fa0/3 Fa0/3 Fa0/2 STP Convergence 6 3- Insignificant Topology Change SW3(config)#interface fastEthernet 0/5 SW3(config-if)#spanning-tree portfast
  21. 21. STP Convergence 7 SW3(config-if)#spanning-tree portfast %Warning: portfast should only be enabled on ports connected to a single host. Connecting hubs, concentrators, switches, bridges, etc... to this interface when portfast is enabled, can cause temporary bridging loops. Use with CAUTION %Portfast has been configured on FastEthernet0/5 but will only have effect when the interface is in a non-trunking mode. 3- Insignificant Topology Change :PORTFAST.
  22. 22. STP Convergence 8 SW3(config)#spanning-tree portfast default 3- Insignificant Topology Change :PORTFAST.
  23. 23. temporary bridging loops Switch1(config)#spanning-tree portfast default Switch2(config)#spanning-tree portfast default
  24. 24. temporary bridging loops 1 2 3 Portfast TBL BPDU GAURD
  25. 25. BPDU GAURD Switch1 Switch2 TRY 1 Switch1,2(config)#spanning-tree portfast default Switch1,2(config)#interface fastEthernet 0/1 Switch1,2(config-if)#spanning-tree bpduguard enable 3- Insignificant Topology Change
  26. 26. BPDU GAURD Switch1 Switch2 TRY 2 Switch1,2,3(config)#spanning-tree portfast default Switch1,2,3(config)#interface fastEthernet 0/1 Switch1,2,3(config-if)#spanning-tree bpduguard enable Fa0/1 Fa0/1 Switch3 3- Insignificant Topology Change : Switch1# sh ip int fa0/1 Error-disable mode
  27. 27. STP Topology Change Kind ----------------------------------------------------------------- 1- Direct Topology Change (30 sec) 2- Indirect Topology Change (50 sec) 3- Insignificant Topology Change (0 sec)
  28. 28. SW1 SW2 SW2 ROOT BRIDGE DPDP RP RP DPBLK PC3PC2 30SERVER1PC2 Direct.30PC BLKSW2RP(FWD). Server1 Example 1
  29. 29. SW1 SW2 SW2 ROOT BRIDGE DPDP RP RP DPBLK PC3 PC2 50SERVER1PC3Indirect .50PC BLKSW2DP(FWD)DPSW3RP. Server1 Example 2
  30. 30. SW1 SW2 SW2 ROOT BRIDGE DPDP RP RP DPBLK PC3 PC2 Server1 1- Direct Topology Change (30 sec) 2- Indirect Topology Change (50 sec) IEEE 802.1d  Slow convergence IEEE 802.1w  Fast convergence
  31. 31. IEEE 802.1d -------------------------------- Disable  BLK Block  BLK Root  FWD Designated  FWD IEEE 802.1w -------------------------------- Disable  BLK Block  BLK Root  FWD (*) Alternate  BLK Designated  FWD (*) Backup  BLK PVSTP RPVSTP
  32. 32. Switch(config)#spanning-tree mode {pvst | rapid-pvst | mst} Select pvst to enable PVST+ (the default setting). Select mst to enable MSTP (and RSTP). Select rapid-pvst to enable rapid PVST+.

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