Well.... Something has to be blocking, right? :) Look at Cat4. 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
Per your own show command there, the local path cost is the same, the local port priority is the same... Port ID's are different (in case we care) . Designated Root has the same MAC on both ports (this is a good thing!), and Designated port MACs are different. Although Designated Path Cost (received path cost) is the same. So the election process: 1. Total accumulated path cost to the root bridge. This is received cost (designated path cost) + local path cost (Port path cost). Here, this is equal either way. 2. If a tie, look at received bridge-id. F0/19 = 001e.be93.9b00 whereas F0/16 = 001e.be93.b080. Here we have two different values. Lower value is preferred. That would be F0/19. 3. If there were still a tie, we'd get into port cost/port-id information but we had no need to get that far. Spanning tree is doing what it's supposed to! Cheers, Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE-M #153, JNCIS-ER, CISSP, et al. CCSI/JNCI-M/JNCI-ER VP - Technical Training - IPexpert, Inc. IPexpert Sr. Technical Instructor [EMAIL PROTECTED] Telephone: +1.810.326.1444 Fax: +1.810.454.0130 http://www.ipexpert.com _____ From: amit chopra [mailto:[EMAIL PROTECTED] Sent: Friday, March 28, 2008 1:51 PM To: [email protected]; [EMAIL PROTECTED] Subject: Spanning-tree election problem in SW4 Problem : Spanning-tree election: Switch topology SW1 (f0/16)-----------------(f0/13)--SW3 | | (f0/13) (f0/19) | | | | | | | | (f0/13) (f0/19) | | 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
