CRC Errors

[rhltechie]

hi All,

I am seeing a very high rate of input errors and crc errors on one of my fast interfaces used for metro e. can this cause a significant slow down in performance? i read online that this could be caused from a duplex mismatch. should I check with my provider to make sure i am set to 100 full on their side as well?

TIA,

R

[sundar.palaniappan · Accepted solution]

Hi,

Indeed, high number of CRCs can cause significant slow down in performance. Any packet that failed the CRC check causes the router to increment the CRC packet counter. When a packet is corrupted the upper layer protocol(s) or application would request retransmission of the packet and that would mean extra wait time for the user.

CRC are typically caused by noise on the line or duplex mismatch. Bandwidth constraints can also cause CRC errors sometimes. Try hardcoding the duplex and in the event that doesn't help physical layer troubleshooting is needed.

Hope that helps!!

Regards,

Sundar

[izreeljames]

@sundar.palaniappan thank you for this breakdown of which you described beautifully.

Perhaps a bit meticulous, but I would like to add greater clarity regarding your following comment :

"When a packet is corrupted the upper layer protocol(s) or application would request retransmission of the packet and that would mean extra wait time for the user."

My reason for commenting is to only add more value with the precision of identifying that  the one of the upper layers: the application layer would have the next lower level: the transport layer, perform the work of error detection and request retransmission. 

"Iron sharpens iron and one man sharpens another" - Proverbs

Best regards,

[Roberto Salazar]

You're right, most of the time CRC is caused by duplex mismatch. When operating at full-duplex, FCS, cyclic redundancy checks (CRC), alignment errors, and runt counters should be minimal. If the link is operating at full-duplex, the collision counter is not active. If the FCS, CRC, alignment, or runt counters are incrementing, check for a duplex mismatch. Duplex mismatch is a situation in which the switch is operating at full-duplex and the connected device is operating at half-duplex, or the other way around. The result of a duplex mismatch is extremely slow performance, intermittent connectivity, and loss of connection. Other possible causes of data link errors at full-duplex are bad cables, a faulty switch port, or NIC software or hardware issues.

http://www.cisco.com/warp/customer/473/46.html

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