Stoping STP

[tarun_cisco]

Hi,

can somoen please explain how can i stop STP processs between two switches ?

[ameya_oke]

Hi Tarun,

You can stop spanning tree by issuing below command.

no spanning-tree vlan

Note: This is not advisable.

https://supportforums.cisco.com/thread/2046805

Please rate if helpful.

Ameya

[Joseph W. Doherty]

Disclaimer

The  Author of this posting offers the information contained within this  posting without consideration and with the reader's understanding that  there's no implied or expressed suitability or fitness for any purpose.  Information provided is for informational purposes only and should not  be construed as rendering professional advice of any kind. Usage of this  posting's information is solely at reader's own risk.

Liability Disclaimer

In  no event shall Author be liable for any damages whatsoever (including,  without limitation, damages for loss of use, data or profit) arising out  of the use or inability to use the posting's information even if Author  has been advised of the possibility of such damage.

Posting

As Ameya notes, this isn't really advisable; curious why you want to stop STP.

[Somasundaram Jayaraman]

Hi,

If you are sure about your network topology, ie. there is no redundant paths which leads to loops then you can disable spanning tree.

++ By default, spanning tree runs on every port. Kindly note that the spanning tree feature cannot be turned off in switches on a per-port basis.

++ you can turn off STP on a per-VLAN basis, or globally on the switch. Extreme care should be taken whenever you disable spanning tree because      this creates Layer 2 loops within the network.

++ Use the no spanning-tree vlan command in order to disable STP on a per virtual LAN (VLAN) basis.

++ Also  ensure that all switches and bridges in the VLAN have spanning tree  disabled. You cannot disable spanning tree on some switches and bridges  in a VLAN and leave it enabled on other switches and bridges in the  VLAN. If you do this, you can have unexpected results because switches  and bridges with spanning tree enabled have incomplete information in  regards to the physical topology of the network.

Please refer the below link for more details

http://www.cisco.com/en/US/customer/tech/tk389/tk621/technologies_configuration_example09186a008009467c.shtml

Hope this answers your question.

Cheers

Somu

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[tarun_cisco]

Thanks everyone.

How about putting the ports in port fast mode.

Say I have as simple as 2 switches with backup link and if I put ports in portfast mode then still STP process will occur?

Sent from Cisco Technical Support iPhone App

[Somasundaram Jayaraman]

Hi,

Port-fast is configured only on access ports. It should not be configured on a trunk link where the two switches getting connected.

SW2(config)#int f0/6

SW2(config-if)#

spann portfast

%Warning: portfast should only be enabled on ports connected to  a single host. Connecting hubs, concentrators,  switches, bridges, etc…  to this interface  when portfast is enabled, can cause temporary  bridging loops.

Use with CAUTION

If you are sure that enabling port-fast will not cause any loops you can use that.

Here’s what happens with the ‘trunk’ option enabled:

SW2(config)#int fa0/6
SW2(config-if)#spann portfast trunk
%Warning: portfast should only be enabled on ports connected to  a single host. Connecting hubs, concentrators,  switches, bridges, etc…  to this interface  when portfast is enabled, can cause temporary  bridging loops.
Use with CAUTION

SW2#sh spanning-tree int f0/6 portfast
VLAN0001         enabled
VLAN0005         enabled
VLAN0007         enabled
VLAN0008         enabled
VLAN0009         enabled
VLAN0010         enabled
VLAN0022         enabled
VLAN0043         enabled
VLAN0058         enabled
VLAN0067         enabled
VLAN0079         enabled
VLAN0146         enabled

Hope this helps.

Cheers

Somu

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[ameya_oke]

Hi Tarun,

It is a wrong notion that portfast stops STP.

Yes it is true that portfast directly takes a switchport in forwarding state but underlying theory is that just the STP states are bypassed.

Now consider there are 3 swithces A,B and C.

Each is connected to one another back to back.

Now even though you configure all uplinks as portfast STP will work.

Reason is that portfast do not stop BPDU transmission.

Now with back to back connectivity in A,B and C we have a Layer 2 loop and thus one port will transition in blocking state.

Only way by which you can ensure STP doesnt work is via no spanning-tree vlan abc cmd.

Please rate the helpful posts.

Ameya

[cadet alain]

Hi,

Yes it is true that portfast directly takes a switchport in forwarding  state but underlying theory is that just the STP states are bypassed

And no TCNs are issued when the port goes up or down.

Regards.

Alain.

[Joseph W. Doherty]

Disclaimer

The    Author of this posting offers the information contained within this    posting without consideration and with the reader's understanding that    there's no implied or expressed suitability or fitness for any  purpose.   Information provided is for informational purposes only and  should not   be construed as rendering professional advice of any kind.  Usage of  this  posting's information is solely at reader's own risk.

Liability Disclaimer

In    no event shall Author be liable for any damages whatsoever  (including,   without limitation, damages for loss of use, data or  profit) arising  out  of the use or inability to use the posting's  information even if  Author  has been advised of the possibility of such  damage.

Posting

And no TCNs are issued when the port goes up or down.

Unsure that's true if a portfast port is "seeing" BPDUs.

There was another recent posting where Peter Paluch noted change in behavior of portfast ports when they see a BPDU, see: https://supportforums.cisco.com/message/3219909#3219909

Peter didn't address whether portfast behavior change impacts TCN too.