Suppose your internet ( May be LAN/WAN / Wireless ) is broken suddenly, Which Factor you will check at that moment?

check the physical layer first

- power (AC or DC, UPS, led lights on Network Devices).

- cables (UTP, STP, Fiber, coaxial) if wire.

- Network devices ports

- Network device OS if it's manageable Devices.

Initial checks are,

1. check the LAN port of our LapTop/Desktop, if LED's are blinking at the LAN port.

2. Check LAN Cable and IO Port.

3. Check power and led status at switch if internet is routed via switch.

4. in case of wireless, check power at wireless modem/RF PoE device.

check the light is coming or gone

second test that connection from the SP is established or lost

I will First check cable connection.

If lan check lan connection both side,

if Wireless check wireless connectivity or restart wireless,

if fiber check with OTDR.

At first we need to check our network adapter and IP configurations then check physical connectivity once our gateway is pinged there is no issue for internal network.

Check Power either coming or not

Check cable it is ok or damage

Check natwork Device

It is always a good practice to investigate from lowest layer to the higest while troubleshooting network problems (i.e. Physical layer to Application layer).

First check for Power Supply and Cable Connection of your netwrok devices (PCs, swithes, routers, wireless controllers or access points)

Next try to ping your default gateway (From your PC using command promt. If you're not aware of your default gateway IP, use command ipconfig on the command promt to check). If you are able to ping your gateway, it indicates that your LAN connection is working and the problem could be with WAN (Internet/ISP) or the website you are trying to reach.

Try reaching a different website, if you are still unable to reach, then it could be WAN (ISP) issue or your proxy server is not working.

Change your proxy and try again. If the problem still perstits, then it is definately an ISP issue.

For wireless, troubleshhoting steps are slightly differnt. follow the intial steps as mentioned above. In case of Wireless (Wifi), check your network signal strength, try getting closer to the wifi device (Modem, Controller or Access point) to improve the strength. If the problem still exists evn after following all of the above steps, then contact your ISP to get a fix from their end.

Sometimes, if it doesnt fix the issue after performing all the steps, turn off your Modem, Router, Wireless Controller for 15-20 seconds and turn it back on. restarting the devices can sometimes fix the issue.

- Wifi Coverage

- Router

- Switches

- Network Cabling

- Network Interface Cards

i may check below step:

1. Check power to equipment

2. check cable/Ports. you may check using LAN Tester for Wired connection. 

3. check network devices on my equipment such as laptop.

I would start with a trace-route to decide if the issue is internal (LAN) or external (ISP)? then zoom in accordingly