Can't set command "spanning-tree mode rapid-pvst" on catalyst 2950

Posted on 2006-07-02
Last Modified: 2012-08-13
Hi Guys

I have a catalyst 2950 switch set up, when i telnet into it and try to set the command "spanning-tree mode rapid-pvst" i lose connection to the switch.

ie (commands i enter):

config t
spanning-tree mode rapid-pvst

Any ideas why???
Question by:jamewang
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Accepted Solution

jfrady earned 168 total points
ID: 17028573
Does your connection come back?  My suspicion is that what you are seeing is a spanning tree converge.  Traffic is being blocked until a new root bridge is elected and the tree calculated.

Expert Comment

ID: 17028612

The command reference says...

Caution: Changing spanning-tree modes can disrupt traffic because all spanning-tree instances are stopped for the previous mode and restarted in the new mode.

spanning-tree mode:

Command specifics are always described in the command references for your catalyst switch and ios version. The main link is


Author Comment

ID: 17028742

So currently i have the following option set on the interface fa0/24 which is the interface i use to telnet into the switch:

 spanning-tree portfast
 spanning-tree bpdufilter enable

Is there a conflicting command somewhere

Assisted Solution

conrad_ray earned 166 total points
ID: 17029796

Portfast and BPDUfilter are considered best practice configs on end user switchports where we do not expect a switch to be connected - only end user PCs/devices. So this config is not conflicting with what we are discussing here.

The reason your connection gets disrupted when you change the STP mode is, as mentioned earlier, due to all STP instances being stopped for the previous mode (say PVST+), and getting restarted for the new mode (rapid-pvst+), hence reconverging.


Assisted Solution

skaap2k earned 166 total points
ID: 17029984
it's just like conrad_ray says, the topology is busy converging, ports are in LISTENING/LEARNING mode... This should take around 20-30seconds before they'll go into FORWARDING mode, at which point, you should be able to reconnect to the switch,

if you cant, perhaps you have a bridge-loop on your network and that port may be blocked, doing a sh spanning-tree blockedports might help you figure that out too. (using a console cable!)

Kind Regards,

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