Frame Check Sequence Failure
Question
A frame that enters a switch fails the Frame Check Sequence. Which two interface counters are incremented? (Choose two.)
Answers
Explanations
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A. B. C. D. E.AD
Whenever the physical transmission has problems, the receiving device might receive a frame whose bits have changed values. These frames do not pass the error detection logic as implemented in the FCS field in the Ethernet trailer. The receiving device discards the frame and counts it as some kind of input error.
Cisco switches list this error as a CRC error. Cyclic redundancy check (CRC) is a term related to how the FCS math detects an error.
The input errors includes runts, giants, no buffer, CRC, frame, overrun, and ignored counts.
The output below show the interface counters with the show interface s0/0/0 command:
When a frame enters a switch, it undergoes a Frame Check Sequence (FCS) check to ensure that it was transmitted without errors. The FCS check calculates a cyclic redundancy check (CRC) value on the data in the frame and appends it to the end of the frame. The receiving switch then recalculates the CRC and compares it to the CRC value in the frame. If the values do not match, the frame is considered to have failed the FCS check and is discarded.
When a frame fails the FCS check, two interface counters are incremented: input errors and CRC errors.
The input errors counter is incremented when a frame is received on an interface but is discarded due to errors, such as FCS errors. This counter is a good indicator of the overall health of an interface, as a high number of input errors can indicate problems with cabling, NICs, or other hardware issues.
The CRC errors counter is specifically incremented when a frame fails the FCS check due to a CRC error. This counter is a useful tool for identifying issues with the physical layer of the network, such as issues with cabling or network interface cards (NICs).
Therefore, the correct answers to this question are D. CRC and A. input errors. The giants and runts counters are incremented when frames exceed the maximum or minimum allowed frame size, respectively. These errors are not related to FCS checks and are not incremented when a frame fails the FCS check.