 Now let us start from physical layer and see what troubleshooting means in physical and data link layer. Physical layer constitutes of all the tangible things that you can see like switches, LED lights, connectors etc. And you have to do some basic checks like the switches are turned on, connectors are connected in right places etc. There are some devices like toner tracers, LAN connectors, connection checkers and multiplexers available which you can use to see if the connections are working correctly or not.