Spanning Tree question for the Gurus

mikeybinec

So I made this little network below to goof around with RSTP. The switches on each end also had one port configured for
vlan 10 (where the hosts plug into).. The weird thing was, that the two end switches showed up as the root bridge for Vlan 10.
So on the left switch, I did a sp vlan 10 root pri. On the right switch I did a sp root sec. The left switch showed the Priority for vlan 10 as 24586 which is correct (32778-4096-4096).. Right switch was configged as sp vlan 10 root sec and the number was
28682 (32778-4096) THEY STILL BOTH SAID THEY WERE THE ROOT FOR VLAN 10

Please tell me this was just a PT flaw, 'cuz I dont recall seeing in any of my books about networks having two root bridges for the same vlan

Thanks all

verbhertz

PT gets all wonky with STP and etherchannels. At least it did in my brief experience testing it. I had to 'copy run start' all my switched and reload them to have STP elect the correct root bridges.

theodoxa

It is also possible...if for some reason the correct Root Bridge's BPDUs were not reaching the other switch. It would (assuming it has the best BPDU otherwise) then see itself as the root bridge.

james43026

Sounds like a PT issue, I suggest saving, closing and reloading the PT file. The swich on the far left hand side is definitely acting as the root bridge, as it is the only switch with all ports in the forwarding state according to the pic provided.