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Cisco 2960S CRC

tim20110612
Level 1
Level 1

Hello,

Does the CRC in Cisco equipment refer to bytes or bits? Thank you very much!

Cisco-2960S#show interfaces tenGigabitEthernet 1/0/1
TenGigabitEthernet1/0/1 is up, line protocol is up (connected)
Hardware is Ten Gigabit Ethernet, address is f4ea.67c3.4733 (bia f4ea.67c3.4733)
MTU 1500 bytes, BW 10000000 Kbit, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ARPA, loopback not set
Keepalive not set
Full-duplex, 10Gb/s, link type is auto, media type is SFP-10GBase-LR
input flow-control is off, output flow-control is unsupported
ARP type: ARPA, ARP Timeout 04:00:00
Last input 6w3d, output 00:00:01, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
5 minute input rate 84000 bits/sec, 28 packets/sec
5 minute output rate 377000 bits/sec, 42 packets/sec
5677611107 packets input, 4615005164223 bytes, 0 no buffer
Received 9511218 broadcasts (8134244 multicasts)
0 runts, 0 giants, 0 throttles
1 input errors, 1 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 8134244 multicast, 0 pause input
0 input packets with dribble condition detected
4631164422 packets output, 2738446223272 bytes, 0 underruns
0 output errors, 0 collisions, 1 interface resets
0 babbles, 0 late collision, 0 deferred
0 lost carrier, 0 no carrier, 0 PAUSE output
0 output buffer failures, 0 output buffers swapped out

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已接受的解答

Jens Albrecht
Level 7
Level 7

Hello @tim20110612,

in fact the CRC count refers to the number of Ethernet frames received with a failed CRC check—not individual bits or bytes.

So your example showing '1 CRC' in the output means one frame with a CRC failure was detected.

HTH!

在原帖中查看解决方案

Hello @tim20110612,

you are welcome!

In case you are interested, the reason is fairly simple. CRC calculates a checksum over the entire incoming frame. If the checksum does not match there is no way to know whether just a single bit or multiple bits were changed. You only know that 'something' is different.

Hence you can only count the number of frames that failed the check.

HTH!

在原帖中查看解决方案

8 条回复8

Jens Albrecht
Level 7
Level 7

Hello @tim20110612,

in fact the CRC count refers to the number of Ethernet frames received with a failed CRC check—not individual bits or bytes.

So your example showing '1 CRC' in the output means one frame with a CRC failure was detected.

HTH!

Thanks Jens!

Hello @tim20110612,

you are welcome!

In case you are interested, the reason is fairly simple. CRC calculates a checksum over the entire incoming frame. If the checksum does not match there is no way to know whether just a single bit or multiple bits were changed. You only know that 'something' is different.

Hence you can only count the number of frames that failed the check.

HTH!

Hello Jens, Your answer is very detailed. Thank you.

balaji.bandi
Hall of Fame
Hall of Fame

Try clear the counters again and observe - see is that CRC errors appears again before going in to deep investigation.

 

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Thanks Balaji

Thanks

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