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CCNP Switch 300-115 - STP - Part 1

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 1

  1. 1. High - Level Sw2#configure terminal Sw2(config)#interface fastEthernet 0/1 Sw2(config-if)#shut No access to servers  Solution : link redundancy ×
  2. 2. High - Level PC1 PC2 PC3 PC4 PC5 PC6 SW2 SW1 SW3 1 2 SRC DES MAC1 -> MAC3 MAC1 -> MAC3 MAC1->MAC3 MAC1->MAC3 MAC1->MAC3 MAC1->MAC3 MAC1 -> MAC3 3 4 1 2 3 4 1 2 34 MAC-ADDRESS-TABLE-SW2 -------------------------------------- PORT MAC -------------------------------------- 1 2 MAC1 3 4 MAC1 MAC-ADDRESS-TABLE-SW1 -------------------------------------- PORT MAC -------------------------------------- 1 MAC1 2 3 4 MAC-ADDRESS-TABLE-SW3 -------------------------------------- PORT MAC -------------------------------------- 1 MAC1 2 3 4 Problem 1 (link redundancy) MAC-Address-Table instability MAC ADDRESS FLAPPING
  3. 3. High - Level PC1 PC2 PC3 PC4 PC5 PC6 SW2 SW1 SW3 1 2 SRC DES MAC1 -> MAC3 MAC1 -> MAC3 MAC1->MAC3 MAC1->MAC3 MAC1->MAC3 MAC1->MAC3 MAC1 -> MAC3 3 4 1 2 3 4 1 2 34 Problem 2 (link redundancy) Frame duplicating MAC1 -> MAC3 MAC1->MAC3
  4. 4. High - Level PC1 PC2 PC3 PC4 PC5 PC6 SW2 SW1 SW3 1 2 SRC DES MAC1 -> BROADCAST MAC1 -> BROADCAST MAC1->BROADCAST MAC1->BROADCAST MAC1->BROADCAST MAC1->BROADCAST MAC1->BROADCAST MAC1 -> BROADCAST 3 4 1 2 3 4 1 2 34 Problem 3 , 4 (link redundancy) Broadcast storm and loop MAC1->BROADCAST MAC1->BROADCAST MAC1->BROADCAST MAC1->BROADCAST MAC1->BROADCAST MAC1 -> BROADCASTMAC1->BROADCAST MAC1->BROADCAST MAC1->BROADCAST
  5. 5. High - Level It is not a spanning-tree It is not a spanning-tree It is a spanning-tree It is a spanning-tree
  6. 6. 100 Mbps 100 Mbps 1 Gbps 100 Mbps 100 Mbps 1 Gbps 100 Mbps 1 Gbps 1 Gbps 100 Mbps 1 2 3 High - Level
  7. 7. STEP 1. Elect a Root Bridge  STP Bridge ID = BID = STP Bridge Priority:MAC  Default STP Bridge Priority=32768  Lowest Bridge ID  switch(config)#spanning-tree vlan VLAN_ID PRIORITY  PRIOITY =( 0,65535) ; 0 , 4096 , 8192 , … , 61440 + example : switch(config)#spanning-tree vlan 1 24576  ROOT BRIDGE : SW1 100 Mbps 100 Mbps 1 Gbps MAC SW1 : 1a12.1516.2399 MAC SW2 : a478.1212.2590 MAC SW3 : ca08.1111.a368 BID SW1 : 32768 : 1a12.1516.2399 BID SW2 : 32768 : a478.1212.2590 BID SW3 : 32768 : ca08.1111.a368 Root bridge STP PROCESS- Step 1 Medium - Level
  8. 8. STEP 2. Select a root port (RP) per switch  COST BW COST --------------------------------------- 10 Mbps 100 100 Mbps 19 1G bps 4 10 Gbps 2  Lowest cost to Root Bridge 100 Mbps 100 Mbps 1 Gbps RP (cost 4) RP (cost 19) STP PROCESS- Step 2 Medium - Level
  9. 9. STEP 3. Select Designated ports per link  Lowest cost to root bridge  role (DP and RP) : state (forward)  role (BLK) : state (not forwarding) 100 Mbps 100 Mbps 1 Gbps DP DP DP RP RP BLK STP PROCESS- Step 3 Medium - Level
  10. 10. SW1 : ROOT BRIDGE SW2 SW3 SW4 SW8 SW7 SW6 SW5 100 Mbps 100 Mbps 100 Mbps 100 Mbps 100 Mbps 100 Mbps 100 Mbps10 Mbps MAC1 < MAC2 < MAC3 < MAC4 < MAC5 < MAC6 < MAC7< MAC8 PRIORITY = 32768 19 214 38 195 57 176 119 114 138 95 157 76 133 100 RP RP RP RP RP RPRP DP DP EXAMPLE DP DP DP DPDPDP BLK BW COST ----------------------------------------------- 10 Mbps 100 100 Mbps 19 1G bps 4 10 Gbps 2 Medium - Level
  11. 11. STP Tie-Breakers 1. Lowest cost 2. Lowest sender BID ( BID(SW1) < BID(SW2) ) 3- Lowest sender port ID  Port ID = (STP port priority(default=128)).(port number) 1 Gbps 1 Gbps 1 Gbps 1 Gbps MAC1 < MAC2 < MAC3 < MAC4 PRIORITY = 32768 SW1 : ROOT BRIDGE SW2 SW3 SW4 G0/1 G0/2 G0/1 (4) G0/2 (12) G0/1 (4) G0/2 (12) G0/1 (8) G0/2 (8) RP RP RP ? RP ? DP DP DP DP EXAMPLE : same cost but different sender bridge ID Medium - Level
  12. 12. EXAMPLE : same cost and same sender bridge ID STP Tie-Breakers 1. Lowest cost 2. Lowest sender BID 3- Lowest sender port ID  Port ID = (STP port priority(default=128)).(port number) MAC1 < MAC2 PRIORITY = 32768 SW1 : ROOT BRIDGE SW2 G0/1 G0/2 G0/2 (4) G0/1 (4) 1 Gbps 1 Gbps PORT ID (G0/1) = 128.1 PORT ID (G0/2) = 128.2 DP DP RP ? RP ? Medium - Level
  13. 13. Page 13June 10, 2018 SCENARIO
  14. 14. Switch#show spanning-tree VLAN0001 Spanning tree enabled protocol ieee Root ID Priority 32769 Address 0006.2A31.0BC0 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 0006.2A31.0BC0 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 Switch# Standard BID : STP bridge priority:MAC Extended BID : (STP bridge priority + VLAN-ID):MAC BID (VLAN 1) : (32768+1):MAC BID (VLAN 2) : (32768+2):MAC Medium - Level
  15. 15. Page 15June 10, 2018 SCENARIO
  16. 16. Page 16June 10, 2018 SCENARIO
  17. 17. Low - Level BPDU (Bridge Protocol Data Unit)  Root bridge , bridge ID  Sender bridge, bridge ID  Root path cost  Sender port ID 100 Mbps 100 Mbps 1 Gbps SW1 SW2 SW3 1 21 2 1 2 1 MAC1 < MAC2 < MAC3 Phase 1
  18. 18. Low - Level 100 Mbps 100 Mbps 1 Gbps SW1 SW2 SW3 21 2 1 2 1 BPDU (Bridge Protocol Data Unit)  Root bridge , bridge ID  Sender bridge, bridge ID  Root path cost  Sender port ID Phase 2
  19. 19. Low - Level 100 Mbps 100 Mbps 1 Gbps SW1 SW2 SW3 21 2 1 2 1 BPDU (Bridge Protocol Data Unit)  Root bridge , bridge ID  Sender bridge, bridge ID  Root path cost  Sender port ID Phase 3
  20. 20. Low - Level 100 Mbps 100 Mbps 1 Gbps SW1 SW2 SW3 21 2 1 2 1 ROOT BRIDGE DP DP RP RP DP BLK

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