If you have 3 spare (lab) switches just hook them up in the classic triangle where there are all hooked togther with a single patch, this is a classic redundancy setup that people use , with it is a built in loop that STP will prevent the loop on , somewhere within that setup you will see a blocked port thus eliminating the loop.
If you use the "spanning-tree bpdufilter enable" interface command on the trunk ports connecting the 2950 switches you will effectively disable spanning-tree on those ports.
As result of this, your switches will not be protected against the loop. Just put any broadcast frame into an access port and you will see the trunk ports blinking continuously, indicating the looped traffic.
If you issue the "show spanning-tree" command, you will not see blocked ports.
Probably you will have a difficulty of access to the console port as well, but you can break the loop by disconnecting a trunk cable.
Now if you issue the "spanning-tree bpdufilter disable" on the trunk ports, you will see that the spanning-tree algorithm works again and you will have one or more blocked ports.
I'm working on a project that includes basic router configurations. I configurated everything including: line console 0, line vty 0 15 and secret passwords. There are 3 routers in the network and every LAN is going t...