Troubleshooting the most common “things are slow” complaint is one of the most difficult calls I get since there are many scenarios and variables to consider.
Root causes range from the malicious (like DDOS or viruses) to the unintentional (like equipment misconfigurations), and everything in between.
I found the most effective approach is trying to eliminate the possible root causes that are easy to prove or disprove. For example, starting up your protocol analyzer of choice connected to any port on the client VLAN could identify layer 2 loops, devices sending out a lot of broadcast multicast packets and misconfigured load balancing.
In this example, when I got the call and performed this check, I got lucky and there it was a layer 2 loop. Many analysts skip this check because they rely on Spanning Tree or Rapid Spanning Tree to prevent this from happening.
In the video below I walk you through how I figured this out and what the issue was.
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