an our custumer as an old C2900XL switch, with IOS 12.0(5.2)XU installed on it. The switch is in VTP client mode.
I noticed that on this switch the STP has been disabled for some VLANs (don't ask me why, it was configured before my company started to manage it), with the command "no spanning-tree vlan X".
I tried to re-enable the spanning tree for all the VLANs in various mode but the STP still remains disabled:
- with the command "spanning-tree vlan X"
- trying to copy a new startup configuration file without the lines "no spanning-tree" and rebooting the switch, but it doesn't worked. I still see those lines in the running config.
- trying to re-enable the STP from the vlan database configuration mode, but I didn't find a command to do that.
- putting the switch in VTP server mode an issuing the command "spanning-tree vlan X", still the same
Do you have any suggestion?
a switch like that has a limitation in the maximum number of STP instances that is probably 64.
Another limit applies to vlans created and propagated by VTP and probably is 128.
So if the vlans in your network are in a number between 64 and 128 the switch is able to participate in VTP but vlans exceeding the limit on STP instances will have STP disabled.
If the vlan number becomes higher then the VTP limit the switch reverts to VTP transparent mode I've seen this during tests on 2950.
Hope to help