Mutiple spanning-tree root bridges

We've started installing some new 3650 switches (replacing 3560's at the access layer) running XE 03.03.05SE. We've run into some problems as a result of "ip device tracking" being on by default, but in the process of debugging I've found that three separate switches all believe they are the spanning-tree root bridge for the same VLANs. The new switches are by default in rapid-pvst mode; the distribution switches are set to rapid-pvst as well. All 3650's are dual-homed.
SW1#sh span vlan 999
VLAN0999
Spanning tree enabled protocol rstp
Root ID    Priority    33767
             Address     78da.6e6f.6d00
             This bridge is the root
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority    33767 (priority 32768 sys-id-ext 999)
             Address     78da.6e6f.6d00
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300 sec
Interface           Role Sts Cost      Prio.Nbr Type
Gi1/1/4             Desg FWD 4         128.52   P2p
Gi2/1/4             Desg FWD 4         128.116 P2p
SW2#sh span vlan 999
VLAN0999
Spanning tree enabled protocol rstp
Root ID    Priority    33767
             Address     f40f.1b84.9680
             This bridge is the root
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority    33767 (priority 32768 sys-id-ext 999)
             Address     f40f.1b84.9680
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300 sec
Interface           Role Sts Cost      Prio.Nbr Type
Gi1/1/3             Desg FWD 4         128.51   P2p
Gi1/1/4             Desg FWD 4         128.52   P2p
SW3#sh span vlan 999
VLAN0999
Spanning tree enabled protocol rstp
Root ID    Priority    33767
             Address     78da.6e6f.7180
             This bridge is the root
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority    33767 (priority 32768 sys-id-ext 999)
             Address     78da.6e6f.7180
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300 sec
Interface           Role Sts Cost      Prio.Nbr Type
Gi1/1/3             Desg FWD 4         128.51   P2p
Gi2/1/4             Desg FWD 4         128.116 P2p
Switch 1 seems to behave as if it is the real root, but this still does not make much sense to me. Does anyone have an explanation? It's been a long time since my switching class, and I very seldom have to deal with spanning-tree issues.

Hi,
Having more than one root switch for a VLAN is definitely a sign of some foul play. A contiguous VLAN can never have more than one root switch. Multiple root switches would occur if, for example, the trunks interconnecting the switches had this VLAN excluded from the list of allowed VLANs, or if they were interconnected by access ports (in a different VLAN) rather than trunks. Another possibility could be an inappropriately constructed MAC ACL or VLAN ACL inadvertently block BPDUs. In any case, this may be a source of serious trouble.
Without further information about your network, it is difficult to suggest anything more specific. Would it be possible to post a diagram explaining your network topology? Also, would it be possible to post the show span root and show span bridge outputs from every switch in your network?
Thank you!
Best regards,
Peter

Similar Messages

Moving spanning tree root bridge

Hello everybody,
I have a lot of vlans trunkated to one link(trunk). If I move root bridge for 1 vlan, do i have impact(recalculating) to all vlans in this trunk or only for this one.
Thanks!

do i have impact(recalculating) to all vlans in this trunk or only for this one??????

Spanning tree root ports in back to back VPC

Ok so I have a question about back to back VPC configuration.
I have a back to back VPC from core to agg layer so that I have 2 logical switches in my path.
However I am seeing an issue on the agg layer. Traffic is traversing the VPC peerlink instead of being sent up to the core which is where the spanning-tree root is configured.
Po1 is my uplink from the agg
Po4 is my vpc peerlink on the Agg
Po1              Root FWD 200       128.4096 (vPC) P2p
Po2              Desg FWD 200       128.4097 (vPC) P2p
Po4              Root FWD 330       128.4099 (vPC peer-link) Network P2p
Eth2/6           Altn BLK 2000      128.262 P2p

a little more info.
Po1 is my uplink to the core
Po4 is my agg vpc peer.
I see 2 paths to root on one swith. it is choosing Po4 (vpc peerlink) instead of Po1 (uplink to core)
MST0000
Spanning tree enabled protocol mstp
Root ID    Priority    4096
             Address     0023.04ee.be01
             Cost        0
             Port        4099 (port-channel4)
             Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority    8192   (priority 8192 sys-id-ext 0)
             Address     547f.eea6.d2c1
             Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Interface        Role Sts Cost      Prio.Nbr Type
Po1              Root FWD 200       128.4096 (vPC) P2p
Po2              Desg FWD 200       128.4097 (vPC) P2p
Po4              Root FWD 330       128.4099 (vPC peer-link) Network P2p
MST0000
Spanning tree enabled protocol mstp
Root ID    Priority    4096
             Address     0023.04ee.be01
             Cost        0
             Port        4096 (port-channel1)
             Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority    8192   (priority 8192 sys-id-ext 0)
             Address     547f.eea6.ce41
             Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Interface        Role Sts Cost      Prio.Nbr Type
Po1              Root FWD 200       128.4096 (vPC) P2p
Po2              Desg FWD 200       128.4097 (vPC) P2p
Po3              Desg FWD 200       128.4098 (vPC) P2p
Po4              Desg FWD 330       128.4099 (vPC peer-link) Network P2p

Change of spanning-tree root

Hi,
Would appreciate some advise on the following:
The network has already been configured with spanning-tree root primary as well as secondary.
Reassigning another switch to be the spanning-tree root primary/secondary, will it cause a downtime in the network? If yes, how long?
Thanks,
Christina

I'm assuming PVST (not rapid-PVST nor MST, that should behave better)
It is very hard to give an exact estimate of a downtime. First, it's not going to be a global downtime. You can basically compare the topology with your current root bridge and the one with your new root bridge. The ports that need to block in the new topology will block quickly, in a matter of few seconds. However, the ports that were blocked in the old topology and that need to be forwarding in the new topology will take a little bit more than 30 seconds to become forwarding (15 second listening + 15 second learning phases). The topology change mechanism will age out stale CAM entries in 15 seconds. If you add a little margin for BPDU propagation, I would estimate that you are looking at a connectivity loss of about a minute, in part of your network.
The more blocked ports need to move from the old to the new topology, the most connectivity loss you will experience. Some feature like uplinfast are able to switchover quickly between their uplinks in case of root ID changing and will reduce the downtime dramatically. It's mainly the core bridges that will take time to unblock their port.
Note that you can expect better convergence time when a better root is introduced in the network (you are lowering the numerical value of the secondary root priority so that it takes over the primary) than when the primary root is downgraded into secondary (you increase the numerical value of the primary root so that it becomes worse than the secondary).
Regards,
Francois

VLAN spanning-tree root and VLAN L3 SVI

I have a traditional core/access switches connected, Catalyst 4506 with 802.1Q uplink trunks to two core 6504-E switches. Spanning-tree roots for VLAN's were on core switch with the active HSRP/SVI. Shutdown HSRP/SVI on the cores and moved the SVI to the L3 access switches, but we left the spanning-tree root on the cores... Is this causing the clients/ports in the VLAN on the access switches to do a double/triple hop over the uplink for ingress/egress? Gig1/1 is the trunkport/uplink to the core, wanted to move L3 functions to the access switch to reduce spanning VLANs across the core network.
Current configuration : 253 bytes
interface Vlan196
description Tower I - 8th Floor VLAN
ip address 10.200.196.1 255.255.255.0
ip access-group 115 in
ip helper-address 164.103.160.150
ip helper-address 172.20.135.201
no ip redirects
no ip unreachables
ip pim sparse-mode
end
I0504506A8#sh spann
I0504506A8#sh spanning-tree vlan 196
VLAN0196
Spanning tree enabled protocol ieee
Root ID    Priority    196
             Address     6400.f1ee.c140
             Cost        4
             Port        1 (GigabitEthernet1/1)
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority    49348 (priority 49152 sys-id-ext 196)
             Address     0015.f960.9ac0
             Hello Time   2 sec Max Age 20 sec Forward Delay 15 sec
             Aging Time 300
Interface        Role Sts Cost      Prio.Nbr Type
Gi1/1            Root FWD 4         128.1    P2p
Gi1/2            Altn BLK 4         128.2    P2p

Hi Tojackson, I guess this depends on how stuff is interconnecting. It's obvious gi1/1 is forwarding and gi1/2 is blocking. So from the furthest access switch, what path must it take to reach gi1/1? That is the number of hops involved for normal traffic.
Now, if you're concerned about a specific VLAN and you need gi1/2 forwarding to reduce travel time for other traffic, you may employ RPVST to have that specific VLAN and cost to go to gi1/2.
In some part of the network I support we have a pair of Cisco 7606 which feeds in to a 4507R and off the 4507R we have a ring of 2955 with even 10-12 L2 switches on the ring. The consequence of multiple layer 2 hops is not of much concern and our spanning tree stops with the 4507 since we're not concerned about broadcast storm on the routed interfaces on the 7600.
-Tom
Please mark answered for helpful posts

Spanning-tree Root changes

Hi All,
I presently have a switched VLAN network (one 6500, several 4912G and 2948Gs) with a 2948G access-layer switch as spanning-tree root.I am planning to change the Spanning tree root to the core 6500 switch running PVST+.All switches are running trunking between them.I have read through the basic STP documents and would like to know any precautions to be aware of before doing it.Any first hand experience will be of great help.
Thanx,
Praful

Praful,
Wise decision to change your root switch, I'd just suggest doing it during your slower periods of time, just-in-case.
It really is a quick change, just expect network connectivity to "pause" for up to 50 seconds while spanning tree stablizes.
Provided you have a good handle on how your network is wired, and you're currently running PVST+ across your network, the actual outage should only be 2-3 seconds. I know I've had to tweak our vlans from time to time and I've never seen it take any longer than 2-3 seconds.
HTH
Steve

Identifying spanning-tree root switch

Looking at a network with a 6509 at the core running in pvst mode. I think the 6509 is the root switch but need to confirm this.
Show spanning-tree gives a bridge id and a root id. My understanding is that the root id should be the MAC address of the root switch.
However I can't find the MAC address given as the root id in the 6509s mac address table, nor in the access switches mac address tables.
I'm sure I'm missing something here - any ideas?

Hi,
in the output of "show spanning-tree" you should look for a line "This bridge is the root". The output will give you the root id and the bridge id of the switch, where you execute the command.
The output looks like this:
Router# show spanning-tree vlan 200
VLAN0200
Spanning tree enabled protocol ieee
Root ID Priority 32768
Address 00d0.00b8.14c8
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Bridge ID Priority 32768
Address 00d0.00b8.14c8
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300
------------- snip -----------
The MAC used for creating the bridge id is not used for forwarding BPDUs and thus does not show up in the CAM table afaik.
To find the root in a switch network, follow the root ports for a given spanning tree instance.
Hope this helps! Please rate all posts.
Regards, Martin

Sg-300 - 3750 stack with SPANNING-TREE root problem.

Morning. I think ive configured a few hundred switches, maybe a thousand in my time, but never have a faced such horribleness that is the SG-300. After this week, I think ill refuse to touch them.
Got 2 voice vlans and running a few vrf's on a 3750 stack. but this discussion is about layer 2.
2 x 3750 stacked
1 x voice switch sg-300 company A voice vlan 18 - Po1 up to 3750 distributed etherchannel Po1 (LACP active both sides) 2 ports in channel
1 x voice switch sg-300 company B voice vlan 19 - Po1 up to 3750 distributed etherchannel Po2 (LACP active both sides) 2 ports in channel
Allowed vlans on both sides (command on Port-channel) are data A, Voice A, Mgt A to switch A
Allowed vlans on both sides (command on Port-channel) are data B, Voice B, Mgt B to switch B
It seems that these switches are limited to one voice vlan....
and that spanning tree BPDU's are ignored (or not recevied- havnt released the shark yet). let me explain.
originally when using "smart port" the switch with the lowest mac address, whatever Voice vlan was configured would take over the other switche's voice vlan, argh what a nightmare.
I gave up on the GUI as its far to complcated and have Almost got this working.
I am now using auto voice vlan, but have disabled smart macro. I hope that disabling smart macro stop other switches from learning the switch with the lowest mac address's voice vlan. So far so good - in the LAB. No where was it documented in the cli guide how do disable this stupid feature.
DHCP is working from scope on core, can mange the switches etc etc, access vlan voice vlan all good (after a monster battle).
Now I have an issue with spanning tree.
spanning tree priority for vlans 1-4094 on the 3750 is 4096.
spanning tree priority for vlans 1-4094 on the SG-300's is 6xxxx.
ALL switches think that they are the root. (well the "logical" 3 of them) The 3750's for all vlans, and the SG-300 for the one instance as it doesnt support per vlan. (I am not interested in trying MST here..this is not a datacentre)
On the 3750's Ive tried ieee, pvst, rpvst, while matching the non per-vlan equivalent on the SG series.
What is the difference between a General port and Trunk Port on a SG-300 specific to spanning tree, native vlans (when you can just configure an untagged vlan anyway!!) and what is the relevance to the way the bpdu's are carried?
And why the need for a PVID, when you can tell a port what is tagged and what isnt.
Does the trunk need Vlan1 to be explicitly allowed, and untagged? Does the Po trunk need to be a general port with PVID configured? in vlan 1?
I need to sort this, as cannot put an access switch into production that thinks it is the root of the tree. I wish I had a 2960.... a 3500XL..anything
Does anyone have CLI commands that can help here?

F.Y.I for catylyst heroes - here is the equivalent config for SG-300 - Vlan1 is required on the allowed list on the catylyst side (3xxx/4xxx/6xxx)
In this example:
VLANS - Voice on 188, data on 57, management on 56.
conf t
hostname XXX-VOICE-SWXX
no passwords complexity enable
username xxxx priv 15 password XXXXX
enable password xxxxxx
ip ssh server
ip telnet server
crypto key generate rsa
macro auto disabled
voice vlan state auto-enabled !(otherwise one switch controls your voice vlan….)
vlan 56,57,188
voice vlan id 188
int vlan 56
ip address 10.230.56.12 255.255.255.0
int vlan1
no ip add dhcp
ip default-gateway 10.230.56.1
interface range GE1 - 2
switchport mode trunk
channel-group 1 mode auto
int range fa1 - 24
switchport mode trunk
switchport trunk allowed vlan add 188
switchport trunk native vlan 57
qos advanced
qos advanced ports-trusted
exit
int Po1
switchport trunk allowed vlan add 56,57,188
switchport trunk native vlan 1
do sh interfaces switchport po1
!CATYLYST SIDE
!Must Explicitly allow VLan1, this is not normal for catalysts - or spanning tree will not work ! Even though it’s the native vlan on both sides.
interface Port-channel1
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 1,56,57,189
switchport mode trunk

Spanning tree guard root

                  Hi,
We have 45xx switch & we enabled spanning tree root guard on ports connected with access switch via fiber uplink
& we enable spanning tree loop guard on access switch side
One of my core switch port connected to Juniper Netscreen Firewall
Whether I need to enable spanning tree guard root on the same port on core switch side ? or not
In case of yes, any config changes required on JUniper Netscreen box
Br/Subhojit

Hi, Pls find the output
Port 130 (GigabitEthernet3/2) of VLAN0054 is designated forwarding
   Port path cost 4, Port priority 128, Port Identifier 128.130.
   Designated root has priority 8246, address 001b.d474.8a40
   Designated bridge has priority 16438, address 001b.0cee.0440
   Designated port id is 128.130, designated path cost 3
   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 filter is enabled
   Root guard is enabled on the port
   BPDU: sent 5847158, received 0
Present the bold config enabled on the port
Br/Subhojit

Two root bridge in same network

Dear Team,
As I checked, there are two root bridge in the same LAN.
We have 6500 which is manually configured as root bridge and this is showing root for all the vlans in the network. Once switch connected to 6500 through 4500 is showing root for the vlans that not assigned to any of the port. Please help to clear it.
Setup
Cisco 6500 -- Cisco 4500 -- Cisco3560 -- Cisco 3560
Cisco 6500
CORE_SW#show spanning-tree root detail
VLAN0001
Root ID Priority 24577
Address 0025.84d9.ac80
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
VLAN0002
Root ID Priority 24578
Address 0025.84d9.ac80
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Cisco 3560 Second
Access#show spanning-tree root de
VLAN0001
Root ID Priority 24577
Address 0025.84d9.ac80
Cost 16
Port 28 (GigabitEthernet0/4)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
VLAN0002
Root ID Priority 32770
Address 000a.b8ff.be00
This bridge is the root
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Here, I have not assigned any port in vlan 2 and this is showing root bridge for vlan 2. In which cases such thing can happen?
Thank You,
Abhisar.

By default, Cisco switches run one spanning tree instance per VLAN and negotiate the topology with other connected switches. If your 3560 believes it is the root for VLAN 2 and there are no ports using VLAN 2, it will consider itself the to be the root because it hasn't been able to negotiate a topology for this VLAN with any other devices. This is normal. Once ports are connected to VLAN 2 and the 3560 can talk to the other switches, the spanning tree will be renegotiated and should behave as you expect.
If you want to have a single spanning tree topology for all VLANs and avoid this behaviour, consider moving to a single-instance MSTP configuration.

SF 300 Serires switch not participating in spanning tree?

I just purchased an SF300-24 managed switch and I am running it in layer3 mode. I am testing it out right now and have it connected to two 2950 switches. The SF300 is connected to each 2950 with a four port etherchannel running LACP. When looking at spanning tree all three switches are configured the same when it comes to hello, forward, max age and all three are in RSTP mode. I adjusted the priorities so that the SF300 would be the root but that is not happening.
I only have one VLAN as of right now set up and connectivity between the three switches is fine. The only problem seems to be that the two 2950 switches are the only two switches involved in the determination of the root bridge. Additionally it was the same way before I configured the etherchannel and had the switches connected over single trunk lines.
I would appreciate if someone can expain to me why this is?
Thanks in advance.

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Thanks for your help but know I still cannot get the three devices to talk MST either,it is getting frustrating. If i add a redundant link and directly connect the two 2950's they immediately talk and configure MST. But when I remove that link no info is passed and both 2950's think they are the root even though the SF 300 priority is 0 on all three MST instances. On the SF300 I have the following settings:
Spanning tree: enabled
STP Operation Mode: Multiple STP
BPDU Handling: Flooding
Path Cost: Long
Region name: test
Revision: 1
Max Hops: 20
Max-age: 20
Hello Time: 2
Forward Delay: 15
MST instance 1 Vlan 100
Bridge Priority 0
Designated Root Bridge: Self
Root port: 0
Root path cost: 0
MST instance 2 Vlan 2-5
Bridge Priority 0
Designated Root Bridge: Self
Root port: 0
Root path cost: 0
MST instance 0 all vlans not in instance 1 and 2
Bridge Priority 0
Designated Root Bridge: Self
Root port: 0
Root path cost: 0
For MST interface Settings (both LAGs/instances are thesame)
Int Priority: 128
Path Cost: 20000
Port State: Boundary
Mode: RSTP
Type: Boundary
Designated port ID: 128
Designated Cost: 0
Remain Hops: 20
Forward Transitions: 1
The 2950 switches: (The only difference on the other switch is that the priority is 8192, and the MACs of course)
MST00 is executing the mstp compatible Spanning Treeprotocol
Bridge Identifierhas priority 4096, sysid 0, address 000b.460e.e040
Configured hello time 2, max age 20, forward delay 15
Current root haspriority 0, address 6c50.4dcb.334b
Root port is 65 (Port-channel1), cost of root path is 50000
Topology change flag not set, detected flag not set
Number of topology changes 7 last change occurred 00:18:54 ago
          from Port-channel1
Times: hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0
Port 65 (Port-channel1) of MST00 is root forwarding
   Port path cost 50000, Port priority 128, Port Identifier 128.65.
   Designated roothas priority 0, address 6c50.4dcb.334b
   Designatedbridge has priority 0, address 6c50.4dcb.334b
   Designated port id is 128.1000, designated path cost 0
   Timers: message age 4, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type ispoint-to-point by default, Boundary RSTP
   BPDU: sent 571,received 568
MST01 is executingthe mstp compatible Spanning Tree protocol
Bridge Identifierhas priority 4096, sysid 1, address 000b.460e.e040
Configured hello time 2, max age 20, forward delay 15
We are the root of the spanning tree
Topology change flag not set, detected flag not set
Number of topology changes 9 last change occurred 00:18:55 ago
          from Port-channel1
Times: hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0
Port 65 (Port-channel1) of MST01 is boundary forwarding
   Port path cost 50000, Port priority 128, Port Identifier 128.65.
   Designated root has priority 4097, address 000b.460e.e040
   Designated bridge has priority 4097, address 000b.460e.e040
   Designated port id is 128.65, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type ispoint-to-point by default, Boundary RSTP
   BPDU: sent 598,received 0
MST02 is executingthe mstp compatible Spanning Tree protocol
Bridge Identifierhas priority 4096, sysid 2, address 000b.460e.e040
Configured hello time 2, max age 20, forward delay 15
We are the root of the spanning tree
Topology change flag not set, detected flag not set
Number of topology changes 9 last change occurred 00:19:50 ago
          from Port-channel1
Times: hold 1, topology change 35, notification 2
          hello 2, max age 20, forward delay 15
Timers: hello 0, topology change 0, notification 0
Port 65 (Port-channel1) of MST02 is boundary forwarding
   Port path cost 50000, Port priority 128, Port Identifier 128.65.
   Designated root has priority 4098, address 000b.460e.e040
   Designated bridge has priority 4098, address 000b.460e.e040
   Designated port id is 128.65, designated path cost 0
   Timers: message age 0, forward delay 0, hold 0
   Number of transitions to forwarding state: 1
   Link type ispoint-to-point by default, Boundary RSTP
   BPDU: sent 611,received 0
I notice that on MST01 and 02 they are not receiving BPDU’s,but I am not sure why or if that is the problem. It appears that the SF 300 is not sending BPDU packets for MST01 and 02, but is sending them for MST00. I also attached a capture. I captured the VLAN info for VLAN 100 which is in MST1. on the SF300, it appears that the SF 300 is recieving STP traffic but not generating any.

Spanning tree in VPC

Hi All,
I have a topology like two vpc peer connected to down catalyst switch 3750 with VPC 51. My left switch is primary in VPC and other is secondary.
So acc. to Theory only primary switch would generate BPDU not secondary switch. But if down catalyst or Secondary switch will be root switch in Spanning tree.
Will primary switch still generate the BPDU's?

Hi Garg,
In VPC environment , In simple term regardless of the Spanning-tree root, VPC primay always generate BPDU and seconday device only rely that bpdu and never generate itself.
For vPC ports only the vPC primary switch runs the STP topology for those vPC ports. In other words, Spanning Tree Protocol for vPCs is controlled by the vPC primary peer device, and only this device generates then sends out Bridge Protocol Data Units (BPDUs) on Spanning Tree Protocol designated ports. This happens irrespectively of where the designated Spanning Tree Protocol root is located. STP on the secondary vPC switch must be enabled but it doesn’t dictate vPC member port state. vPC secondary peer device proxies any received Spanning Tree Protocol BPDU messages from access switches toward the primary vPC peer device . Both vPC member ports on both peer devices always share the same STP port state (FWD state in a steady network).
HTH
Regards,
VS.Suresh.
*Plz rate the usefull posts *

What is the command to check the changes in the spanning-tree topology?

What is the command to check the changes in the spanning-tree topology?

Hi,
Few commands which would help are:
1- Show spanning-tree detail
2-show spanning-tree detail | in ieee|from|occur|is exec >> This will give from were the changes occuring- Ex:
C6K1#show spanning-tree detail | in ieee|from|occur|is exec
VLAN0001 is executing the rstp compatible Spanning Tree protocol
Number of topology changes 9536 last change occurred 00:00:29 ago
from GigabitEthernet4/6
3- show spanning-tree active *& show spanning-tree root >> Will give you the root information.
4- show spanning-tree inconsistentports >> If there are any port which are inconsistent state due to STP features.
STP running MST:
===============
show spanning-tree mst configuration >> Need to check and match the same outputs with the other switches running in the same MST domain/region.
show spanning-tree mst detail
show spanning-tree mst <name of the region>
Debug on STP:
============
debug spanning-tree events/bpdu >> would be good but to be run with more cautious.
HTH
Inayath
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Debug spanning-tree bpdu brought the network down

I'm troubleshooting a pair of Dell Power-Connect switches in a Dell blade chassis connected to a pair of Cisco 4900M switches. I have my 4900M switches set as spanning-tree root and backup root. The Dell switches are connected via LACP trunks to the 4900M's. Dell switch 1 to 4900 #1 and Dell switch 2 to 4900M #2. Both of the Dell switches are reporting as root switches.
I was trying to troubleshoot this yesterday and ran 'debug spanning-tree bpdu' on the primary 4900M. There was a masive amount of BPDU events scrolling by. This debug command actually took the network down. The primary 4900M was non-responsive and the secondary unit had it's CPU go to 100%. The fix was to power cycle the primary 4900M.
Why did this command take my network down?
--Patrick

Typically, the device prioritizes console output ahead of other functions. The debug spanning-tree bpdu generates a lot of output. That is what jumped the CPU to 100% and ultimately caused the device to crash.
You should be very careful with debug commands and log to the internal buffer, instead of the console.
See: http://www.cisco.com/c/en/us/support/docs/dial-access/integrated-services-digital-networks-isdn-channel-associated-signaling-cas/10374-debug.html.

Spanning tree question

I want to change the spanning tree root on several vlans on my network. My question is, will this cause STP to recalculate for the entire network, which can cause the network to slow down or will it only affect the vlans that I am changing? I want to make sure I am not going to impact anything on the network.

When executed properly, this will only affect the vlans that you wish to change. Use the folllowing command to change spanning tree prio on a vlan:
spanning-tree vlan xx priority 4096 (or a multiple of 4096 for less priority)
Be aware that there is always a risk of unexpected disruptions when you do this. The vlans that you change may still carry user traffic altough there are no users on it. If your topology and traffic flow are not exactly as you assume they are, more vlans may be affected. It is therefore not advisable to alter this setting during peak-hours.
Regards,
Leo

Mutiple spanning-tree root bridges

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