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New Member

Question: Why no spanning-tree vlan 1? on the switch

Good afternoon,

Would you please help me with the questions below on the Cisco 2950 Switch?

1-I wonder why command "no spanning-tree vlan 1"?  What is the situation we should use this?

2-What does it mean?

3-Is this by default?

Thank you very much.

7 REPLIES
Bronze

Re: Question: Why no spanning-tree vlan 1? on the switch

I wouldn't recommend using this.  Basically it turns spanning tree of within the vlan.  Some people use it if they "shut" the vlan down.  Shutting vlan 1 is something you should do.  Turning spanning tree off on a shutdown vlan isn't an issue, but if someone accidentally "no shut"s it could cause a loop.

New Member

Re: Question: Why no spanning-tree vlan 1? on the switch

Hi danrya,

Thank you for your help.  I just want to confirm if I understand your suggestion correct. So your suggestion is to turn on spanning tree for VLAN 1 right?

What is the default for Spanning tree for VLAN1?

Thanks again,

New Member

Re: Question: Why no spanning-tree vlan 1? on the switch

Hi,

From my understanding, generally while configuring the switch, many of us Shut down VLAN 1. and it is done when we change our Native vlan, and then disables the default one. In such senario, we can get no spanning-tree vlan 1, to avoid VLAN 1 STP instance on the switch. This will prevent any accidental STP instance for VLAN 1.

By default for VLAN 1, STP work normally selecting root bridge on either based on priority or MAC address for VLAN 1. Default all switch runs PVST, so if we have default priority on all our bridges, then priority would be, 32769 ( 32768 + 1). then the selection will be based on MAC address of the bridge. This selection process you can override with either changing priority of any of your bridge or by applying command to make it root brigde.

Regards,

Hardik...

New Member

Hello. In conclusion, is

Hello.

 

In conclusion, is recommend to use "no spanning tre vlan 1" or no?

 

Please Replay.

 

Best Regards

Cisco Employee

Hi,In conclusion, is

Hi,

In conclusion, is recommend to use "no spanning tre vlan 1" or no?

Never, ever! Doing this - deactivating STP in VLAN1 - is crying out loud for trouble.

On Cisco Catalyst switches, VLAN 1 itself cannot be deleted, shutdown or suspended. danrya was not correct in stating that VLAN 1 can be shutdown or suspended. On current Catalyst platforms, most certainly, it cannot. Even if all ports are moved to a different VLAN, the native VLAN on trunks is changed to a different value and VLAN 1 remains completely unused from the administrator's point of view, many Cisco protocols (CDP, VTP, DTP, ...) are still carried in VLAN 1 so the VLAN 1 is continuously operating. If STP was deactivated in VLAN 1 and the switched network had redundancy in it, VLAN 1 would remain unprotected against switching loops. It would be only a matter of time till a broadcast, multicast or an unknown destnation unicast was introduced into VLAN 1 and had the network go down.

So, my recommendation is: Never turn off STP, neither in VLAN 1, nor in any other VLAN. STP is there to protect you, and even if you think you do not need that protection, the real life may prove you otherwise (everyone - you, or your fellow administrators, or your users - make mistakes and it's so easy to loop two ports with a seemingly disconnected patch cable). It's always better to be safe than sorry.

Best regards,
Peter

Super Bronze

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Posting

As Peter has already noted, it's generally not a good idea to shut down STP.  However, if you're running STP, you might want to convert to the rapid-STP.  (NB: I recall, older 2950 IOS images don't support it, but the last IOS images for that series do.)

Never think about it, unless

Never think about it, unless you want to invite some trauma :)

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