Common Wireshark Mistakes: Tips for Effective Packet Analysis

Packet analysis with Wireshark isn’t just challenging - it’s a real test of patience and attention to detail. The microscopic binary-level details can be overwhelming, and over time, I’ve realized that some of the biggest hurdles come from mistakes we make as analysts. Here, I’ll share five lessons I’ve learned from experience to help you avoid these common pitfalls.

Mistake 1: Capturing too large PCAP files

Early in my journey, I made this mistake repeatedly. I’d set Wireshark to capture traffic and walk away, only to return hours later to a massive file that my system could barely handle. One time, I ended up with over a terabyte of traffic - a nightmare to sift through.

Lesson learned: Break your captures into manageable pieces using a ring buffer. This trick has saved me countless hours. Configure Wireshark to create 500 MB files and limit the number of files:

-t ring-buffer -b filesize:500 -b files:100        

Now, when an issue arises, I can zero in on the relevant time frame without wading through endless data.

Mistake 2: Allowing too much noise

I’ll never forget the first time I captured traffic on a noisy machine. The browser had dozens of tabs open, Spotify was playing, and emails were syncing. When I opened the PCAP, it was a mess. I spent hours filtering out irrelevant traffic instead of solving the actual problem.

Lesson learned: Before capturing, close everything non-essential on the machine under test. Shut down browsers, streaming services, and email clients. This way, your PCAP will be cleaner, and you’ll save yourself a lot of frustration.

Mistake 3: Chasing false alarms

False alarms have wasted more of my time than I’d like to admit. Whether it’s duplicate packets, oversized frames, or misleading TCP windows, I’ve gone down these rabbit holes too many times.

Duplicate packets

Once, I thought my network was falling apart because every packet seemed to have a retransmission. Turns out, I was capturing duplicates from a span port setup. Matching IP identification numbers clued me in.

Oversized packets

Another time, I was puzzled by 14,000-byte packets. I spent hours troubleshooting “jumbos” before realizing they were a result of segmentation offloading. The NIC had segmented the packets after the capture point.

Small TCP windows

Small TCP window sizes had me convinced there was a throughput issue. In reality, I’d missed the TCP handshake, so Wireshark couldn’t apply the window scaling factor.

Lesson learned: Pause and verify before diving into troubleshooting. Understand your capture environment and double-check anomalies before assuming they’re issues.

Mistake 4: Capturing traffic in the wrong location

Capturing in the wrong spot has burned me more than once. I’d set up my device, thinking I was in the right place, only to realize later that I’d missed critical traffic.

Lesson learned: Use taps or properly configure span ports to ensure you’re capturing the right data. Double-check your setup to avoid wasting time on incomplete captures.

Mistake 5: Failing to duplicate the problem

Intermittent issues are the bane of packet analysis. I’ve spent hours waiting for a problem to happen again, only to walk away and miss it.

Lesson learned: Set up ongoing packet captures with a ring buffer. This ensures you’re always ready when the issue occurs. Once, I captured an intermittent problem that had been plaguing a client for weeks, simply by having a capture running in the background.

Bonus Tip: use filters effectively

One of my early mistakes was not using filters. I’d stare at endless lines of traffic, trying to find what I needed. Learning to filter changed everything. For example, to filter HTTP traffic:

http        

Or to capture traffic only from a specific IP:

host 192.168.1.1        

Lesson learned: mastering filters makes your life infinitely easier. Focus on what matters and let Wireshark do the heavy lifting.

Packet analysis isn’t just about mastering Wireshark - it’s about working smarter. By avoiding these mistakes and adopting these lessons, you can streamline your workflow and focus on solving the real issues. As to me - every mistake is a chance to learn and improve.