when we put cat-6 cable from PoE to switch. switch shows heavy traffic. all lights blink fastely. there is no other connection on switch. we have removed all cables. only one cable from mikrotik PoE to swith is there. who is generating traffice???

Are you trying to power the MikroTik from a poe port on a switch? What routerboard do you have?

this smells to a loop?

My first thought was a loop but he said there are no other connections to the switch....?

routerboard is 411. connection is
radio ethernet port to Poe port & poe port to switch ethernet port. there is no other cable to switch. still light blink. help me..

Are you saying you have a power injector and from it you have one cable going from the PoE out to the rb411 PoE in? Then another cable from the PoE LAN port to the switch?
You say there are no other cables connected to the switch or the rb411 correct?

Can you give more detail about what switch you have and if there really is anything else connect to it or the rb411.

What your saying doesn't make much sense.. you could have a bad cable or faulty power injector. As mentioned in another post it sounds like you have a loop in the network but... who knows. Take a picture, draw something up, whatever it takes to get your point across better.

Check you cable and termination, poorly terminated or incorrectly terminated connections can cause this.