We are using this switch as L3 and planning to run some ACL to stop bad traffic. I never run ACL on switches so wondering is there any performance impact or how bad it will be? if anyone has any experience or supporting data?

More details, we have lots of UDP traffic pretty much streaming so just wanted to mention because small packet size also impact CPU.

Does nexus platform use Hardware base ACL or software base ACL?

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    Apr 1, 2018 at 19:26

1 Answer 1


That 3K and 9K platforms don't really have a notion of software switching. If it can't be programmed in the forwarding ASIC then it's not forwarded. There are a couple of minor exceptions but for standard unicast/multicast forwarding it's going to either go in hardware or not at all.

This, incidentally, is why the number of ACL's supported on these platforms is so limited (on the 3K in particular).

Also - packet size/volume/bandwidth doesn't really have an effect on CPU on these platforms but there is some PPS limit on the ASIC complex. I don't recall the specifics of the 3064 in particular but it should be at least in the close vicinity of line rate.

That said, instead of tracking CPU (...as would be the case on an older IOS box) you may want to pay close attention to buffer utilization...especially if you're running a speed mismatch on the box (i.e. 1G <-> 10G).

  • This is a great answer. It's exactly, as mentioned, very important to keep an eye on the buffers.
    – user36472
    Jan 6, 2018 at 11:05
  • How to check buffer size utilization on Nexus? We have all device running on 10g nic speed.
    – Satish
    Jan 6, 2018 at 15:11
  • The documentation is freely available: cisco.com/c/en/us/td/docs/switches/datacenter/nexus3000/sw/qos/…
    – rnxrx
    Jan 6, 2018 at 17:38
  • @rnxrx I read that link and its useful but is there any command to see realtime buffer usage because i found none
    – Satish
    May 27, 2018 at 18:54
  • nevermind found this command show hardware internal buffer info pkt-stats detail cisco.com/c/en/us/products/collateral/switches/…
    – Satish
    May 27, 2018 at 19:03

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