Nexus 5K high ping time

[neteng2323]

I am setting up 2 Nexus 5548s that are going to be the Layer 3 distribution switch for a building. They are in a VPC Peerlink.   I currently have 2 layer 3 links back to a 7K.  They are connected via single mode fiber between buildings.  I am currently getting high response times when pinging from 5k-->7K and 7K--->5K on both 5Ks. Average times are 6-9ms.  It starts at 2ms and jumps to 9 pretty quickly. I have tested fiber, changed SFP's etc and get the same results. I have another layer 3 connection (in production) from 7K to the same closet as the 5K's and get 0-1ms, which is what I was expecting.  

I've read a little bit about 5548s having CoPP control plane policing but I don't think I'm sending enough ICMP for it to be dropping packets and affecting my ping tests.  

[Rajeshkumar Gatti]

If the ping through the box is at a lower latency then what you are dealing with is how the CPU is handling the ICMP packets. CoPP will police the flows so you will typically see drops if CoPP rate limit is hit. If the latency is higher that means that either the 5k or the 7k is allocating CPU cycles for more priority tasks which causes responses for ICMP to be delayed.

I would run an ethanalyzer on the 5k and the 7k to see what type of traffic is hitting the CPU. Also I would check the processes utilization on these switches to rule out any high CPU.

For 7k ( There is a section for ethanalyzer)

http://www.cisco.com/c/en/us/support/docs/interfaces-modules/nexus-7000-series-supervisor-1-module/116137-trouble-nexus7000-highcpu-00.html

Nexus 5k : Ethanalyzer

http://www.cisco.com/c/en/us/support/docs/switches/nexus-5000-series-switches/116201-technote-ethanalyzer-00.html

Note: Typically if you are not seeing any issues and just concerned about this behavior then go ahead with the ethanalyzer option and checking the CPU.

If you are dealing with packet loss for traffic through the switch and other unexplained issues then see if you can engage TAC. Troubleshooting latency in packet response when switch CPU is involved can be a red herring from experience and doesn't usually lead to solving the main problem.

-Raj

P.S: Rate threads that helps as it saves time for your peers with similar issues.