Can anyone tell me a valid reason why disabling spanning-tree should be considered. Everything I have read cautions against it. Just wondering if there is something I missing.
Here is an example of some of the configs I am running into on switches in the network that I am new to. No one else can tell me why this was done.
spanning-tree mode pvst
no spanning-tree optimize bpdu transmission
spanning-tree extend system-id
no spanning-tree vlan 33,64,66-67,120,152-156,176,180,184,197,202,225,402,671
no spanning-tree vlan 701,703-705,777,997,999-1000
there are no good enough reasons to disable STP on a Vlan.
However, depending on the switch platforms some of them with PVST have some scalability limits:
you can find some C2950 or other that can run only 64 instances of STP.
The same devices usually have also a limit on how many vlans they can learn from VTP but the two limits can be different.
In a device like this vlans created /learned after having reached the limit are automatically in STP off and you see lines as the ones you have placed in your post.
So I would suggest you to explore this network by noticing also switch model, IOS version, number of vlans defined in the campus.
use sh vlan
sh spanning-tree summary
If instead these are C6500 or C4500 what you see is a human choice that can be discussed
Hope to help