Problem : Spanning-tree election:
Switch topology
SW1 (f0/16)-----------------(f0/13)--SW3
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(f0/13) (f0/19)
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(f0/13) (f0/19)
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SW2 (f0/19)----------------(f0/16)---SW4
Guys - Can anybody help me :- The problem is that I am not able to find out
the answer why port f0/16 of SW4 is in
blocking stage towards to SW2.
Please not the primary root for vlan 20 is SW1. The cost of all the
links is 19.
SW1#show spanning-tree vlan 20
VLAN0020
Spanning tree enabled protocol ieee
Root ID Priority 24596
Address 001e.be93.8a80
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24596 (priority 24576 sys-id-ext 20)
Address 001e.be93.8a80
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 15
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Fa0/13 Desg FWD 19 128.15 P2p
Fa0/16 Desg FWD 19 128.18 P2p
SW2#show spanning-tree vlan 20
VLAN0020
Spanning tree enabled protocol ieee
Root ID Priority 24596
Address 001e.be93.8a80
Cost 19
Port 15 (FastEthernet0/13)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32788 (priority 32768 sys-id-ext 20)
Address 001e.be93.b080
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 15
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Fa0/13 Root FWD 19 128.15 P2p
Fa0/19 Desg FWD 19 128.21 P2p
SW3#show spanning-tree vlan 20
VLAN0020
Spanning tree enabled protocol ieee
Root ID Priority 24596
Address 001e.be93.8a80
Cost 19
Port 15 (FastEthernet0/13)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32788 (priority 32768 sys-id-ext 20)
Address 001e.be93.9b00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Fa0/13 Root FWD 19 128.15 P2p
Fa0/19 Desg FWD 19 128.21 P2p
SW4#show spanning-tree vlan 20
VLAN0020
Spanning tree enabled protocol ieee
Root ID Priority 24596
Address 001e.be93.8a80
Cost 38
Port 21 (FastEthernet0/19)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32788 (priority 32768 sys-id-ext 20)
Address 001e.be93.a100
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- --------
--------------------------------
Fa0/16 Altn BLK 19 128.18 P2p
Fa0/19 Root FWD 19 128.21 P2p
*Here is the spanning-tree deatils for all 4 switch.*
SW1 :
Port 15 (FastEthernet0/13) of VLAN0020 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.15.
Designated root has priority 24596, address 001e.be93.8a80
Designated bridge has priority 24596, address 001e.be93.8a80
Designated port id is 128.15, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 18082, received 3
Port 18 (FastEthernet0/16) of VLAN0020 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.18.
Designated root has priority 24596, address 001e.be93.8a80
Designated bridge has priority 24596, address 001e.be93.8a80
Designated port id is 128.18, designated path cost 0
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 18089, received 11
SW2 :
Port 15 (FastEthernet0/13) of VLAN0020 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.15.
Designated root has priority 24596, address 001e.be93.8a80
Designated bridge has priority 24596, address 001e.be93.8a80
Designated port id is 128.15, designated path cost 0
Timers: message age 2, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 3, received 18036
Port 21 (FastEthernet0/19) of VLAN0020 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.21.
Designated root has priority 24596, address 001e.be93.8a80
Designated bridge has priority 32788, address 001e.be93.b080
Designated port id is 128.21, designated path cost 19
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 3157, received 14887
SW3 :
Port 15 (FastEthernet0/13) of VLAN0020 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.15.
Designated root has priority 24596, address 001e.be93.8a80
Designated bridge has priority 24596, address 001e.be93.8a80
Designated port id is 128.18, designated path cost 0
Timers: message age 1, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 11, received 18059
Port 21 (FastEthernet0/19) of VLAN0020 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.21.
Designated root has priority 24596, address 001e.be93.8a80
Designated bridge has priority 32788, address 001e.be93.9b00
Designated port id is 128.21, designated path cost 19
Timers: message age 0, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 569, received 2
SW4
Port 18 (FastEthernet0/16) of VLAN0020 is blocking
Port path cost 19, Port priority 128, Port Identifier 128.18.
Designated root has priority 24596, address 001e.be93.8a80
Designated bridge has priority 32788, address 001e.be93.b080
Designated port id is 128.21, designated path cost 19
Timers: message age 2, forward delay 0, hold 0
Number of transitions to forwarding state: 2
Link type is point-to-point by default
BPDU: sent 14887, received 3185
Port 21 (FastEthernet0/19) of VLAN0020 is forwarding
Port path cost 19, Port priority 128, Port Identifier 128.21.
Designated root has priority 24596, address 001e.be93.8a80
Designated bridge has priority 32788, address 001e.be93.9b00
Designated port id is 128.21, designated path cost 19
Timers: message age 2, forward delay 0, hold 0
Number of transitions to forwarding state: 1
Link type is point-to-point by default
BPDU: sent 2, received 581
