I have several locations with managed network switches - for example, one being a stack of 3com 4500's. On occasion we have an issue where a user somewhere in the building decides to plug in their own consumer grade switch, which is fine until they accidentally create a loop back by plugging a cable from one port to the other!
This ends up causing all kinds of havoc on the network, basically effectively taking it down in most cases.
Is there a way I can prevent this (and hopefully detect it if it happens)?
I believe that's what Spanning Tree Protocol (STP) is for, correct?
I see the device has a configuration screen for "MSTP", and by port and device I can configure it. Here is an example port MSTP status currently:
----[Port22(Ethernet1/0/22)][FORWARDING]---- Port Protocol :enabled Port Role :CIST Designated Port Port Priority :128 Port Cost(Dot1T) :Config=auto / Active=200000 Desg. Bridge/Port :32768.0022-5782-5900 / 128.22 Port Edged :Config=enabled / Active=enabled Point-to-point :Config=auto / Active=true Transmit Limit :10 packets/hello-time Protection Type :None MSTP BPDU format :Config=auto / Active=legacy Port Config Digest Snooping :disabled Rapid Fwd State :Rapid Forwarding Num of Vlans Mapped :2 PortTimes :Hello 2s MaxAge 20s FwDly 15s MsgAge 0s RemHop 20 BPDU Sent :426 TCN: 0, Config: 0, RST: 0, MST: 426 BPDU Received :0 TCN: 0, Config: 0, RST: 0, MST: 0
And the device status:
-------[CIST Global Info][Mode MSTP]------- CIST Bridge :32768.0022-5782-5900 Bridge Times :Hello 2s MaxAge 20s FwDly 15s MaxHop 20 CIST Root/ERPC :32768.0022-5782-5900 / 0 CIST RegRoot/IRPC :32768.0022-5782-5900 / 0 CIST RootPortId :0.0 BPDU-Protection :disabled TC-Protection :enabled / Threshold=6 Bridge Config Digest Snooping :disabled TC or TCN received :0 Time since last TC :0 days 16h:52m:12s
Device ports status:
MSTID Port Role STP State Protection 0 Ethernet1/0/2 DESI FORWARDING NONE 0 Ethernet1/0/3 DESI FORWARDING NONE 0 Ethernet1/0/4 DESI FORWARDING NONE 0 Ethernet1/0/5 DESI FORWARDING NONE ... etc ...