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Analyze the STP problem
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03-23-2003
09:18 PM
- last edited on
03-25-2019
02:45 PM
by
ciscomoderator
There are three cisco switches in my network, which are connected as following:
3550-12T <--------> 3550-24-EMI
\ /
\ /
\ /
2950T-24
I configured 802.1q trunk between the two 3550 switches, and links between 2950 and 3550 are access layer type. The configuration of each switch is attached at the end. I set 3550-12T as primary root switch for VLAN15, and 3550-24-EMI as secondary root switch for VLAN15, and 2950T-24 is connected to the access ports of 3550 switches( belong to VLAN15). When I checked the spanning tree status of the three switches, I found the port of 3550-24-EMI connecting to 2950T-24 is in the block state, while in 2950T-24, the corresponding port is still in the forwarding state. And I also found the STP instances of the two switches are different. Can anyone help me analyze the problem? And give me some advices. Thanks in advance.
3550-12T:
...
hostname cnccb-sw1
spanning-tree extend system-id
spanning-tree vlan 1 priority 24576
spanning-tree vlan 9 priority 24576
spanning-tree vlan 10 priority 24576
spanning-tree vlan 11 priority 24576
spanning-tree vlan 12 priority 24576
spanning-tree vlan 13 priority 24576
spanning-tree vlan 15 priority 24576
!
interface GigabitEthernet0/1
switchport access vlan 13
switchport mode access
no ip address
!
interface GigabitEthernet0/2
switchport access vlan 13
switchport mode access
no ip address
!
interface GigabitEthernet0/3
switchport mode access
no ip address
!
interface GigabitEthernet0/4
switchport mode access
no ip address
!
interface GigabitEthernet0/5
switchport access vlan 9
switchport mode access
no ip address
!
interface GigabitEthernet0/6
switchport access vlan 10
switchport mode access
no ip address
!
interface GigabitEthernet0/7
switchport access vlan 9
switchport mode access
no ip address
!
interface GigabitEthernet0/8
switchport access vlan 15
switchport mode access
no ip address
!
interface GigabitEthernet0/9
description connected to WS-C2950T-24 (Port GigabitEthernet0/1)
switchport access vlan 15
switchport mode access
no ip address
!
interface GigabitEthernet0/10
description connected to WS-C3550-24-EMI (Port FastEthernet0/24)
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1-12,15-4094
switchport mode trunk
no ip address
!
interface GigabitEthernet0/11
no ip address
!
interface GigabitEthernet0/12
no ip address
!
interface Vlan1
no ip address
shutdown
!
interface Vlan9
ip address 172.31.9.253 255.255.255.0
no ip redirects
no ip route-cache
no ip mroute-cache
standby 9 ip 172.31.9.254
standby 9 priority 200
standby 9 preempt
standby 9 track Vlan9 40
!
interface Vlan10
ip address 172.31.10.253 255.255.255.0
no ip redirects
no ip route-cache
no ip mroute-cache
standby 10 ip 172.31.10.254
standby 10 priority 200
standby 10 preempt
standby 10 track Vlan10 40
!
interface Vlan11
ip address 172.31.11.253 255.255.255.0
no ip redirects
no ip route-cache
no ip mroute-cache
standby 11 ip 172.31.11.254
standby 11 priority 200
standby 11 preempt
standby 11 track Vlan11 40
!
interface Vlan12
ip address 172.31.12.253 255.255.255.0
no ip redirects
no ip route-cache
no ip mroute-cache
standby 12 ip 172.31.12.254
standby 12 priority 200
standby 12 preempt
standby 12 track Vlan12 40
!
interface Vlan13
ip address 172.31.13.254 255.255.255.0
no ip route-cache
no ip mroute-cache
!
interface Vlan15
ip address 172.31.15.253 255.255.255.0
no ip redirects
no ip route-cache
no ip mroute-cache
standby 15 ip 172.31.15.254
standby 15 priority 200
standby 15 preempt
standby 15 track Vlan15 40
!
router ospf 110
log-adjacency-changes
redistribute static subnets
network 172.31.9.0 0.0.0.255 area 0
network 172.31.10.0 0.0.0.255 area 0
network 172.31.11.0 0.0.0.255 area 0
network 172.31.12.0 0.0.0.255 area 0
network 172.31.13.0 0.0.0.255 area 0
network 172.31.15.0 0.0.0.255 area 0
!
...
VTP Configuration:
cnccb-sw1#show vtp status
VTP Version : 2
VTP Operating Mode : Server
VTP Domain Name : Soliton
VTP Pruning Mode : Disabled
VTP V2 Mode : Enabled
VTP Traps Generation : Disabled
3550-24-EMI:
...
hostname cnccb-sw2
spanning-tree extend system-id
spanning-tree vlan 1 priority 28672
spanning-tree vlan 9 priority 28672
spanning-tree vlan 10 priority 28672
spanning-tree vlan 11 priority 28672
spanning-tree vlan 12 priority 28672
spanning-tree vlan 14 priority 24576
spanning-tree vlan 15 priority 28672
!
!
!
interface FastEthernet0/1
switchport access vlan 14
switchport mode access
no ip address
no cdp enable
!
interface FastEthernet0/2
switchport access vlan 14
switchport mode access
no ip address
no cdp enable
!
interface FastEthernet0/3
switchport mode access
no ip address
no cdp enable
!
interface FastEthernet0/4
switchport mode access
no ip address
no cdp enable
!
interface FastEthernet0/5
switchport access vlan 9
switchport mode access
no ip address
no cdp enable
!
interface FastEthernet0/6
switchport access vlan 11
switchport mode access
no ip address
no cdp enable
!
interface FastEthernet0/7
switchport access vlan 9
switchport mode access
no ip address
no cdp enable
!
interface FastEthernet0/8
switchport access vlan 11
switchport mode access
no ip address
no cdp enable
!
interface FastEthernet0/9
description connected to WS-C2950T-24 (Port FastEthernet0/24)
switchport access vlan 15
switchport mode access
no ip address
no cdp enable
!
interface FastEthernet0/10
switchport mode access
no ip address
no cdp enable
!
...
interface FastEthernet0/24
decription connected to WS-C3550-12T (Port GigabitEthernet0/10)
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1-12,15-4094
switchport mode trunk
no ip address
no cdp enable
!
interface GigabitEthernet0/1
no ip address
no cdp enable
!
interface GigabitEthernet0/2
no ip address
no cdp enable
!
interface Vlan1
no ip address
no ip mroute-cache
shutdown
!
interface Vlan9
ip address 172.31.9.252 255.255.255.0
no ip redirects
no ip mroute-cache
ip ospf cost 20
standby 9 ip 172.31.9.254
standby 9 priority 100
standby 9 preempt
!
interface Vlan10
ip address 172.31.10.252 255.255.255.0
no ip redirects
no ip mroute-cache
ip ospf cost 20
standby 10 ip 172.31.10.254
standby 10 priority 100
standby 10 preempt
!
interface Vlan11
ip address 172.31.11.252 255.255.255.0
no ip redirects
no ip mroute-cache
ip ospf cost 20
standby 11 ip 172.31.11.254
standby 11 priority 100
standby 11 preempt
!
interface Vlan12
ip address 172.31.12.252 255.255.255.0
no ip redirects
no ip mroute-cache
ip ospf cost 20
standby 12 ip 172.31.12.254
standby 12 priority 100
standby 12 preempt
!
interface Vlan14
ip address 172.31.14.254 255.255.255.0
no ip mroute-cache
ip ospf cost 20
!
interface Vlan15
ip address 172.31.15.252 255.255.255.0
no ip redirects
no ip mroute-cache
ip ospf cost 20
standby 15 ip 172.31.15.254
standby 15 priority 100
standby 15 preempt
!
router ospf 110
log-adjacency-changes
redistribute static subnets
network 172.31.9.0 0.0.0.255 area 0
network 172.31.10.0 0.0.0.255 area 0
network 172.31.11.0 0.0.0.255 area 0
network 172.31.12.0 0.0.0.255 area 0
network 172.31.14.0 0.0.0.255 area 0
network 172.31.15.0 0.0.0.255 area 0
!
...
cnccb-sw2#show vtp status
VTP Version : 2
VTP Operating Mode : Server
VTP Domain Name : Soliton
VTP Pruning Mode : Disabled
VTP V2 Mode : Enabled
VTP Traps Generation : Disabled
WS-C2950T-24
...
hostname cnccb-sw3
spanning-tree extend system-id
!
interface FastEthernet0/1
switchport mode access
no ip address
storm-control broadcast level 70.00
storm-control multicast level 70.00
storm-control action shutdown
storm-control action trap
!
...(FastEthernet0/2 - 0/23 is configured the same as port 0/1)
!
interface FastEthernet0/24
decription connected to WS-C3550-24-EMI (Port FastEthernet0/9)
switchport mode access
no ip address
!
interface GigabitEthernet0/1
decription connected to WS-C3550-12T(Port GigabitEthernet0/9)
switchport mode access
no ip address
!
interface GigabitEthernet0/2
switchport mode access
no ip address
storm-control broadcast level 70.00
storm-control multicast level 70.00
storm-control action shutdown
storm-control action trap
!
interface Vlan1
ip address 172.31.15.247 255.255.255.0
no ip route-cache
!
ip default-gateway 172.31.15.254
Spanning tree status:
cnccb-sw1 (2550-12T)
VLAN0015
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 000b.5f8c.55c0
Cost 4
Port 9 (GigabitEthernet0/9)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32783 (priority 32768 sys-id-ext 15)
Address 000b.5f79.8380
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Port ID Designated Port ID
Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr
---------------- -------- --------- --- --------- -------------------- --------
Gi0/9 128.9 4 FWD 0 32769 000b.5f8c.55c0 128.25
Gi0/10 128.10 19 FWD 4 32783 000b.5f79.8380 128.10
cnccb-sw2 (3550-24-EMI):
VLAN0015
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 000b.5f8c.55c0
Cost 19
Port 9 (FastEthernet0/9)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32783 (priority 32768 sys-id-ext 15)
Address 000b.5f42.0d00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Port ID Designated Port ID
Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr
---------------- -------- --------- --- --------- -------------------- --------
Fa0/9 128.9 19 FWD 0 32769 000b.5f8c.55c0 128.24
Fa0/24 128.24 19 BLK 4 32783 000b.5f79.8380 128.10
cnccb-sw3 (2950T-24)
cnccb-sw3#show spanning-tree
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address 000b.5f8c.55c0
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 000b.5f8c.55c0
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Port ID Designated Port ID
Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr
---------------- -------- --------- --- --------- -------------------- --------
Fa0/3 128.3 19 FWD 0 32769 000b.5f8c.55c0 128.3
Fa0/4 128.4 19 FWD 0 32769 000b.5f8c.55c0 128.4
Fa0/7 128.7 19 FWD 0 32769 000b.5f8c.55c0 128.7
Fa0/8 128.8 19 FWD 0 32769 000b.5f8c.55c0 128.8
Fa0/9 128.9 19 FWD 0 32769 000b.5f8c.55c0 128.9
Fa0/18 128.18 19 FWD 0 32769 000b.5f8c.55c0 128.18
Fa0/19 128.19 19 FWD 0 32769 000b.5f8c.55c0 128.19
--More--
Interface Port ID Designated Port ID
Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr
---------------- -------- --------- --- --------- -------------------- --------
Fa0/20 128.20 19 FWD 0 32769 000b.5f8c.55c0 128.20
Fa0/21 128.21 19 FWD 0 32769 000b.5f8c.55c0 128.21
Fa0/23 128.23 19 FWD 0 32769 000b.5f8c.55c0 128.23
Fa0/24 128.24 19 FWD 0 32769 000b.5f8c.55c0 128.24
Gi0/1 128.25 4 FWD 0 32769 000b.5f8c.55c0 128.25
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03-23-2003 09:20 PM
Sorry the diagram is:
3550-12T <--------> 3550-24-EMI
\ /
\ /
\ /
2950T-24
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03-23-2003 10:47 PM
Just some notes. It seems that your objective for the root bridge was not
achieved. Based on the spanning-tree information, the elected root bridge
is the 2950. From the spanning-tree output, all switches are using the
default priority of 32768 and the 2950 became the root bridge because it
has the lowest MAC address. There's an inconsistency with your config and
the output of the show spanning-tree. For example in the 3550-12T, you have
configured a priority of 24576 but the spanning-tree shows 32783.
You might want to try the following config:
[3550-12T or (cnccb-sw1)]
no spanning-tree vlan 15 priority 24576
spanning-tree vlan 15 root primary
[3550-24 or (cnccb-sw2)]
no spanning-tree vlan 15 priority 28672
spanning-tree vlan 15 root secondary
HTH.
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03-24-2003 07:16 AM
Thank you very much!
Sorry, i pasted the early command output. The output corresponding with the configuration is as following:
cnccb-sw1:
VLAN0015
Spanning tree enabled protocol ieee
Root ID Priority 24591
Address 000b.5f79.8380
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 24591 (priority 24576 sys-id-ext 15)
Address 000b.5f79.8380
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 15
Interface Port ID Designated Port ID
Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr
---------------- -------- --------- --- --------- -------------------- --------
Gi0/9 128.9 4 FWD 0 24591 000b.5f79.8380 128.9
Gi0/10 128.10 19 FWD 0 24591 000b.5f79.8380 128.10
cnccb-sw2:
VLAN0015
Spanning tree enabled protocol ieee
Root ID Priority 24591
Address 000b.5f79.8380
Cost 19
Port 24 (FastEthernet0/24)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 28687 (priority 28672 sys-id-ext 15)
Address 000b.5f42.0d00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Port ID Designated Port ID
Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr
---------------- -------- --------- --- --------- -------------------- --------
Fa0/9 128.9 19 BLK 4 32769 000b.5f8c.55c0 128.24
Fa0/24 128.24 19 FWD 0 24591 000b.5f79.8380 128.10
cnccb-sw3:
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 24591
Address 000b.5f79.8380
Cost 4
Port 25 (GigabitEthernet0/1)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address 000b.5f8c.55c0
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
Interface Port ID Designated Port ID
Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr
---------------- -------- --------- --- --------- -------------------- --------
Fa0/3 128.3 19 FWD 4 32769 000b.5f8c.55c0 128.3
Fa0/4 128.4 19 FWD 4 32769 000b.5f8c.55c0 128.4
Fa0/7 128.7 19 FWD 4 32769 000b.5f8c.55c0 128.7
Fa0/8 128.8 19 FWD 4 32769 000b.5f8c.55c0 128.8
Fa0/9 128.9 19 FWD 4 32769 000b.5f8c.55c0 128.9
Fa0/18 128.18 19 FWD 4 32769 000b.5f8c.55c0 128.18
--More--
Interface Port ID Designated Port ID
Name Prio.Nbr Cost Sts Cost Bridge ID Prio.Nbr
---------------- -------- --------- --- --------- -------------------- --------
Fa0/19 128.19 19 FWD 4 32769 000b.5f8c.55c0 128.19
Fa0/20 128.20 19 FWD 4 32769 000b.5f8c.55c0 128.20
Fa0/21 128.21 19 FWD 4 32769 000b.5f8c.55c0 128.21
Fa0/23 128.23 19 FWD 4 32769 000b.5f8c.55c0 128.23
Fa0/24 128.24 19 FWD 4 32769 000b.5f8c.55c0 128.24
Gi0/1 128.25 4 FWD 0 24591 000b.5f79.8380 128.9
I noted in cnccb-sw3, there runs a different spanning-tree instance with itself as the root switch. How can i place them in one spanning-tree instance without changing the ports connecting 2950 to 3550 switches to trunk ports?
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03-24-2003 06:06 PM
Just to make it clear, when you mentioned "I noted in cnccb-sw3, there runs a different
spanning-tree instance with itself as the root switch.", are you talking about ports
Fa0/3-4,7-9,... which are in forwarding state? The "FWD" status for ports connected to
hosts or servers is normal. From the STP output, cnccb-sw3 is running VLAN 1 only.
I think the problem is with the 2950's configuration. In your post you have the ff:
!
interface FastEthernet0/24
decription connected to WS-C3550-24-EMI (Port FastEthernet0/9)
switchport mode access
no ip address
!
interface GigabitEthernet0/1
decription connected to WS-C3550-12T(Port GigabitEthernet0/9)
switchport mode access
no ip address
!
The above configuration uses VLAN 1 the default VLAN.
You have to assign Fa0/24 and Gi0/1 to VLAN 15 also:
!
interface FastEthernet0/24
switchport access vlan 15
!
interface GigabitEthernet0/1
switchport access vlan 15
!
You should alo check the status of trunks ports and the allowed VLANs on those trunks.
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03-24-2003 07:00 PM
I mean in the show spanning-tree command output in 2950, there says "this bridge is the root" for vlan 1, so I think the STP instance runs in 2950 is different from STP instance runs in 3550 switches. Because if all the three switches run one STP instance, there should have only one root switch for vlan 1.
If I set the f0/24 and g0/1 to vlan 15, i have to set all other ports in 2950 to vlan 15. I am not sure this will combine the two STP instances. I will test it.
Thanks very much.
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