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Background:

We are observing a high interface load (spikes up to 1G) on a WAN (dedicated link) uplink port of a Cisco switch. How can we find the IP of the client that is causing this high load?

I have done some research before asking: I have looked at NetFlow manual, but could not find any examples of matches relevant to my problem. Also, we don't have a network monitoring host to send the traffic to. I have also come across IP Accounting, but it is deprecated for our switch.

This is a new install.

Our hardware is Cisco Nexus 5672UP, 7.3(0)N1(1)

Could someone please suggest a set of commands (potentially involving NetFlow in cached mode) to get from an interface name to a table of IP addresses with their transient bandwidth usages?

  • What is the switch model and IOS version? You should look at the Network Engineering Question Checklist for guidance. – Ron Maupin May 29 '18 at 14:06
  • You should be able to monitor excessive usage on your firewall. – Zac67 May 29 '18 at 14:53
  • @RonMaupin Thank you, I have updated the question – Tony Sepia May 29 '18 at 15:28
  • @Zac67, thank you, but on that segment of network there isn't a firewall – Tony Sepia May 29 '18 at 15:29
  • OK. You now have me confused. You claim it is Cisco IOS, but it is really a Nexus switch that does not use IOS, it uses NX-OS. Those are very different things. – Ron Maupin May 29 '18 at 15:30
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Netflow is supported on the 5600's but NXOS doesn't provide the same local information that IOS does (ex: no show ip cache flow equivalent).

You'll need to collect the Netflow on an external host and run something like a top-talkers query. There are a ton of commercial and open source tools for Netflow analysis but bear in mind that the 5600 only supports sampled Netflow. This isn't a big deal for your use case and most modern Netflow analyzers support sampling.

  • Thank you! I have accepted the answer. Any chance of you providing a set of commands (like the question mentions), so that I can see an example of how to configure matches for this particular problem? I don't want to make them too broad, but instead see a good example for configuring them to relay the minimum required metrics. – Tony Sepia May 30 '18 at 9:31
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There might be some other solutions to your problem. Netflow is one way. Another keyword could be "ip accounting" but you have also to read the manuals. For a quick look and if you have the possibillity to configure a monitor/span port, you can use an ordinary laptop with wireshark to get the information needed.

  • Thank you, that is a good piece of advice. I was hoping to find a sequence of NetFlow configuration commands (for local cache, not sending to monitoring server). Something that would keep only the essnetial bits of information that we need to get the answer – Tony Sepia May 29 '18 at 15:31

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