Output errors on N5k 10G interfaces

[pille1234]

Good evening gentlemen,

today I witnessed a cisco n5k that stopped playing fair. For a yet unkown reason several interfaces started to show output errors all begining within the same second. While i instantly thought this would be a wiring issue I began to ask myself what an output error actually means. Can anybody help me with that question? Google usually brings up output drops, not regular output errors. So what is it and how can a 10G fiber interface even detect that there is a problem without receiving what it was sending?

I'd appreciate your input on that matter

bye

Pille

[nkarpysh · Accepted solution]

Hi Pille,

Output errors can be caused by many things. N5k is cut-through so it is starting to send packet before it get it's all from the sender. So you may need to check if you see any input errors on the other interfaces (on N5k or FEX)accompanying the output ones. It can also be related to jumbo frame coming trough with Jumbo option not set up.

For jumbo you can refer to:

http://www.cisco.com/en/US/docs/switches/datacenter/nexus5000/sw/qos/421_n2_1/Cisco_Nexus_5000_Series_NX-OS_Quality_of_Service_Configuration_Guide_Rel_421_N2_1_chapter3.html#con_1150612

To check it in more details can you please share following logs:

• show run int ex/y
  
• show interface counters error
  
• show hardware internal carmel port ethX/Y
  
• sh hard int gatos port eX/Y
  
• sh hard int gatos counters interrupt  | egrep -i crc|drop|stomp
  

Thanks,

Nik

[pille1234]

Thanks Nik,

your suggestion about the input errors on another interface were spot on. We had fcs inbound errors on one of the n5k vpc peer link interfaces, that's probably why so many different interfaces were struck by outgoing errors at the same time. A change of the affected sfp solved our problem

Once again thanks Nik for your help.

Regards

Pille