I have 7 switches (3750 catalyst) connected (stackwise) I just added an extra switch (3750) but with a cat 6 cross cable. I connected the cable from port 24 of the first switch in stack to the newly placed switch port 24. When I plugged in the cable spanning-tree began to run on the switch in the stack. I have rapid-pvst enabled on all switches, so all my servers attached to switch 1 in stack lost connection. Is it normal that this switch went in spanning-tree status? and why?
Each switch starts out being the root until they hear the BPDUs of other switches, then they figure out who comes out on top. During this time, spanning tree ports move through different modes where it is only listening to BPDU packets. Where I'm foggy is whether any competing BPDU from another switch is enough to trigger a convergence to the tree. Inidividual ports in portfast mode may still pass data (i'm not certain), but BPDU-partiicipating ports defintiely get affected. During the first two port states of STP convergence All other traffic is dropped. It can take 15-45 seconds for a network to converge and agree upon who is the bridge root and elimiante all duplicate paths to the root. With multiple vlan and PVST each VLAN runs a separate instance of spanning tree, and can establish a ifferent root and spanning tree configuration. Large spanning tree domains are a PITA. I just reconfigured a 75-switch campus-wide vlan configuration to elimiante spanning tree problems.