It should look something like this.
sh spanning-tree root
Root Hello Max Fwd
Vlan Root ID Cost Time Age Dly Root Port
---------------- -------------------- --------- ----- --- --- ------------
VLAN0001 0 0007.yyyy.xxxx 0 2 20 15
VLAN0003 32768 0006.aaaa.bbbb 3012 2 20 15 Gi7/14
VLAN0005 0 0007.yyyyxxxx 0 2 20 15
VLAN0006 0 0007.yyyy.xxxx 0 2 20 15
In the example here VLAN1, 5 and 6 are all on the switch I am connected to for their spanning-tree root.
You can also see that VLAN 3's root has a different MAC address and is "known" down port Gi7/14.
A Sh cdp nei detail gigabit 7/14 detail ( gigabit 7/14 because my port above is gi7/14 so substitute your own ) will bring you to the device that is the root of that SP for that VLAN. If it's a link off a link you may have to do this once or twice more to get there - you will know when you are there as the port will be blank.
when on that switch do a sh cdp nei which will return something like... ( Anonymised by me)
Device ID Local Intrfce Holdtme Capability Platform Port ID
Router Gig 0/1 154 R S I WS-C6509 Gig 3/1
roof Fas 0/40 125 T AIR-BR350 fec0
switch Gig 0/2 125 S I WS-C3560- Gig 0/2
Switch2 Fas 0/11 152 T S WS-C3548- Fas 0/4
Take note of your switch name ( the bit before the # ) and if it appears under DeviceID then you have a loop. Local Intrfce and PortID will tell you the 2 ports that are looped.
