spanning-tree root given me bad values

[Rowlands Price]

Dear Support,

I have a big network with many switches, sometimes my network is unaccessible. to get the netwoek back, i reload all switches

I have many 4506 and others 3560 and so

There are many vlans on the switch. here is the stp config on central switch

spanning-tree mode pvst
spanning-tree extend system-id
spanning-tree uplinkfast
spanning-tree vlan 1-10,13-25,29-57,59-600 priority 8192
spanning-tree vlan 11-12,26,28,58 priority 16384
spanning-tree vlan 2,8 forward-time 10
spanning-tree vlan 2,8 max-age 14

The problem is in all the network, when a execute the sh spa root, i have very high cost of the root port

Rimac#sh spanning-tree root

Root Hello Max Fwd
Vlan Root ID Cost Time Age Dly Root Port
---------------- -------------------- --------- ----- --- --- ------------
VLAN0001 8193 000c.ce76.c6c0 6010 2 20 15 Gi0/2
VLAN0002 8194 000c.ce76.c6c0 3010 2 14 10 Gi0/2
VLAN0003 8195 000c.ce76.c6c0 3010 2 20 15 Gi0/2
VLAN0004 8196 000c.ce76.c6c0 3010 2 20 15 Gi0/2
VLAN0005 8197 000c.ce76.c6c0 3010 2 20 15 Gi0/2
VLAN0006 8198 000c.ce76.c6c0 3010 2 20 15 Gi0/2

are theses values correct?

Thanks for your quick support

[AFROJ AHMAD · Accepted solution]

Hi ,

I believe that adjusting the "path cost" will enable you to control which port is blocked on the switch.

The command is:
switch(config-if)# spanning-tree cost <cost>


If a loop occurs, spanning tree uses the path cost when selecting an interface to place
into the forwarding state. A lower path cost represents higher-speed transmission.
For cost, the range is 1 to 200000000; the default value is derived from the media speed
of the interface.

Thanks-

Afroz

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[Rowlands Price]

Hi Afroz

Thanks for your response.

I don't know where to adjust the path cost because it's appears on all the switchs of my network.

there are about 50 switchs on the network, and on each network, there are  hight,

below is the "sh spa root" for a switch, vlan 82 is  very high

switch23#sh spanning-tree root
Root Hello Max Fwd
Vlan Root ID Cost Time Age Dly Root Port
---------------- -------------------- --------- ----- --- --- ------------
VLAN0081 8273 000c.ce76.c6c0 6025 2 20 15 Gi0/1
VLAN0082 8238 000c.ce76.c6c0 12075 2 20 15 Gi0/1
VLAN0083 8275 000c.ce76.c6c0 6025 2 20 15 Gi0/1
VLAN0084 8276 000c.ce76.c6c0 6025 2 20 15 Gi0/1
VLAN0085 8277 000c.ce76.c6c0 6025 2 20 15 Gi0/1

[AFROJ AHMAD]

Hi ,

I understand it is not easy to track it but you need to see which all devices has to be in forwarding state when there is a chance of loop.

Thanks-

Afroz

[Rowlands Price]

Hi 

where start tracking exactly and what?

Will track each port of every switches?

see attached a piece of the network.

[Rowlands Price]

Hi All,

i understand why i have very high value from the sh spanning-tree root/

It's because of this command: spanning-tree uplinkfast

the spanning-tree uplinkfast change the switches STP defaut values to another new values,

it's change the switch priority from 32768 to 49152 and change all ports cost value to 3000.

This is why i have these values.