How To Troubleshoot Interface and Cable Issues?

Pre-requisites: Types of Collisions

Collision refers to the scenario in which two stations transmit frames at the same time. In that case, both frames may be dropped or retransmitted. You can check whether a device is connected to a device just by watching the LED associated with the interface. A green light indicates that the interface is connected to another device while orange and red tell that there is a problem.

Case 1:

You can also check the connection or not connected state of a switch interface using the command

show interface <interface>

These are the possible combination that can happen with interface and line protocol:

1. Up & UP
2. UP & Down
3. Down & Down

We have already seen case 1, and it means that everything is working as intended.

Case 2:

The reason that this could be happening:

1. The opposite site device interface is in shutdown mode.

Case 3:

Reasons:

1. The cable is not connected.
2. The cable is faulty.
3. Another end is not connected properly.

Checking Errors and Collisions:

You can check errors and collisions using the same command:

show interface <interface>

Type	Explanation
Collisions	The number of times a collision occurred before the interface transmitted a frame to the media successfully.
Giants	Frames received exceed the maximum frame size.(1518 bytes)
Runts	Frames received that are smaller than the least maximum frame size.(64 bytes)
Late-Collisions	the collision that occurs after 512 bits of the frame have been transmitted.
ignored	The number of received packets is ignored by the interface because of the interface.
Input errors	This includes runts, giants, no buffer, CRC, frame, overrun, and ignored counts.