VLAN-STP

Answered Question
Aug 3rd, 2010

Hi,

I white the command on Switch 1 is Primary root bridgeVLAN 10 and Secondary root bridge 1001.

But now problem is both VLAN is show "This bridge is the root" but not showing the primary or secondary.

I know I have to concentrate on BID and RID value so escape this, how I can see which primary and secondary by another method.

!

spanning-tree vlan 1001 priority 28672
spanning-tree vlan 10 priority 4096

!

SW1#sh spanning-tree

VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     000a.4152.b880
             Cost        19
             Port        48 (FastEthernet0/48)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
             Address     000a.f41a.5180
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/48           Root FWD 19        128.48   P2p


VLAN0010
  Spanning tree enabled protocol ieee
  Root ID    Priority    4106
             Address     000a.f41a.5180
            This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    4106   (priority 4096 sys-id-ext 10)
             Address     000a.f41a.5180
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/48           Desg FWD 19        128.48   P2p


VLAN1001
  Spanning tree enabled protocol ieee
  Root ID    Priority    29673
             Address     000a.f41a.5180
             This bridge is the root
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

  Bridge ID  Priority    29673  (priority 28672 sys-id-ext 1001)
             Address     000a.f41a.5180
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
             Aging Time 300

Interface        Role Sts Cost      Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
Fa0/48           Desg FWD 19        128.48   P2p

I have this problem too.
0 votes
Correct Answer by krahmani323 about 6 years 4 months ago

Sorry just 'show spanning-tree root' you should get something like this ===>

Switch#sh spanning-tree root

                                         Root    Hello Max Fwd
Vlan                   Root ID          Cost    Time  Age Dly  Root Port
---------------- -------------------- --------- ----- --- ---  ------------
VLAN0001          4097 000e.8338.0100         0    2   20  15
VLAN0019          4115 000e.8338.0100         0    2   20  15
VLAN0020          4116 000e.8338.0100         0    2   20  15
VLAN0021          4117 000e.8338.0100         0    2   20  15
VLAN0022          4118 000e.8338.0100         0    2   20  15
VLAN0023          4119 000e.8338.0100         0    2   20  15
VLAN0254         33022 0008.21b2.b300        23    2   20  15  Gi0/12
VLAN0994         33762 0008.21b2.b300        23    2   20  15  Gi0/12

Regards.

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abhi-adte Tue, 08/03/2010 - 06:32

lets consider I am using only one switch

!

spanning-tree vlan 1001 priority 28672
spanning-tree vlan 10 priority 4096

!

krahmani323 Tue, 08/03/2010 - 06:59

Hello Abhinay,

From a Cisco switch If you want to have a summarized view of who is root for each vlan => show spanning-tree root will give a clear view of the Root bridge ID per vlan.

About secondary root, there is no way to query or listen to the network to find another potential secondary root simply because there are no advertisements or elections of secondary root bridges (only for the root).

==> Indeed in the BPDU configuration message content there is a "Root Bridge ID" field (which is exchanged and known by every switch participating in the STP instances) which identifies who is the root for each vlan, but there is no 'secondary root bridge ID' or any relative field.

As you may know for the command :  " spanning-tree vlan vlan-id root {primary | secondary} [diameter diameter] " is a macro command that executes several other commands.

=> This command logic applies when the configuration command is executed; it does not dynamically change the priority if another switch later advertises a better priority.

Hope it helps.

Kind regards.

Karim

abhi-adte Tue, 08/03/2010 - 08:34

SW1#sh spanning-tree vlan 1 root ?
  address       Mac address of the root bridge
  cost          Path cost from this bridge to the root
  detail        Detailed of the status and configuration
  forward-time  Forward delay interval for the spanning tree topology
  hello-time    Hello time for the spanning tree topology
  id            Spanning tree root bridge identifier
  max-age       Max age for the spanning tree topology
  port          Root port
  priority      Bridge priority of the root bridge
  |             Output modifiers
 

after SW1#sh spanning-tree vlan 1 root no command support.

Correct Answer
krahmani323 Tue, 08/03/2010 - 08:38

Sorry just 'show spanning-tree root' you should get something like this ===>

Switch#sh spanning-tree root

                                         Root    Hello Max Fwd
Vlan                   Root ID          Cost    Time  Age Dly  Root Port
---------------- -------------------- --------- ----- --- ---  ------------
VLAN0001          4097 000e.8338.0100         0    2   20  15
VLAN0019          4115 000e.8338.0100         0    2   20  15
VLAN0020          4116 000e.8338.0100         0    2   20  15
VLAN0021          4117 000e.8338.0100         0    2   20  15
VLAN0022          4118 000e.8338.0100         0    2   20  15
VLAN0023          4119 000e.8338.0100         0    2   20  15
VLAN0254         33022 0008.21b2.b300        23    2   20  15  Gi0/12
VLAN0994         33762 0008.21b2.b300        23    2   20  15  Gi0/12

Regards.

abhi-adte Tue, 08/03/2010 - 10:53

heyyy Thanks...

I didn't get exact answer but it's ok coz root bridge cost is always 0 and others are different depend on topology.

then we can trace how many 0 cost of vlan and in between we can see which is primary and secondary.

Thanks once...

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