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New Member

strange network disconnection issue

I am currently have an issue on a catalyst express 500 switch (POE) whereby the link to the rest of the network (link into 3560 switch) disconnects whenever i unplug or plug anything in to the ce500. the voice and data (dont ask why!!) are on the same vlan so essentially the switch doesnt need to be doing anything clever. all it needs to do is what a dumb switch would do. anyone have ideas as to why this would happen!?

Cisco Employee

Re: strange network disconnection issue


How exactly does it "disconnect"? Does it go down, or does the LED go amber for, say, 30 seconds and then comes back? What exactly do you do to make the link work again? And also, what kind of STP do you run in your network?

Best regards,


New Member

Re: strange network disconnection issue

Hi Peter,

thanks for replying.

when i plug the catalyst express switch into the 3560 and set up coresponding 802.1q ports, its doesnt work. if i set one port to access and the other to trunk and turn STP off on the VLAN on the catalyst express switch, it allows pings through, but then as soon as something unplugged or plugged in, the link to the other switch drops.

STP issue? STP mode on the other switches in the network is mst.

loopguard default.

the only way i can re-gain the connection is to enable then disable the port that links to the other switch. but then again whenever something disconnects or connects it drops again.

many thanks,


Hall of Fame Super Silver

Re: strange network disconnection issue

Hello Jack,

CE 500 does not support VTP, you need to create vlans manually like in a VTP transparent switch, so they are not plug and play as everyone could think.

Hope to help


New Member

Re: strange network disconnection issue

Hi Guiseppe,

The thing is, the CE500 doesnt really need to know about the vlans. it is plugged into an access port and doesnt work unless i set up the CE500 port as a trunk and turned the STP off on the vlan (native).

it would work its just its clever enough to know that its plugged into another switch (CDP i guess) so wont let me set up an access port on the CE500 and shuts the port down if i try and do this. BPDU guard??

i would just like to know why it disconnects when something is plugged in or unplugged?!!

many thanks,