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[Video] VLAN Analysis with Wireshark 2.0

May 16, 2017

Learn VLAN Analysis with Wireshark 2.0

When I teach Wireshark classes, I commonly get asked, “What do I do when I get back to my desk?”, “What if I can’t span a port, or don’t have a TAP?”

I typically show my attendees dozens of “Baselines” that would only take a few minutes to complete.

Here’s an example of one of my favorite baselines; Start a capture and analyze whatever you see. No taps, span or mirror ports.

All the packets you see will be there for a reason from certain devices based on their current configuration. I won’t kid you, the first time you go through this it might take a bit of time, but when you get the hang of it you will be able to identify how devices are configured and how to tune them.

Getting Started with VLAN Analysis

In this video I show you some tips and tricks to get you started and create filters for captures of IPv4, IPv6, STP, SSDP, CDP, as well as how to define end points.


Let me know if you find this helpful and I will make more videos covering other protocols and scenarios.

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Heartbeats Packets Inside the Bypass TAP

If the inline security tool goes off-line, the TAP will bypass the tool and automatically keep the link flowing. The Bypass TAP does this by sending heartbeat packets to the inline security tool. As long as the inline security tool is on-line, the heartbeat packets will be returned to the TAP, and the link traffic will continue to flow through the inline security tool.

If the heartbeat packets are not returned to the TAP (indicating that the inline security tool has gone off-line), the TAP will automatically 'bypass' the inline security tool and keep the link traffic flowing. The TAP also removes the heartbeat packets before sending the network traffic back onto the critical link.

While the TAP is in bypass mode, it continues to send heartbeat packets out to the inline security tool so that once the tool is back on-line, it will begin returning the heartbeat packets back to the TAP indicating that the tool is ready to go back to work. The TAP will then direct the network traffic back through the inline security tool along with the heartbeat packets placing the tool back inline.

Some of you may have noticed a flaw in the logic behind this solution!  You say, “What if the TAP should fail because it is also in-line? Then the link will also fail!” The TAP would now be considered a point of failure. That is a good catch – but in our blog on Bypass vs. Failsafe, I explained that if a TAP were to fail or lose power, it must provide failsafe protection to the link it is attached to. So our network TAP will go into Failsafe mode keeping the link flowing.

Glossary

  1. Single point of failure: a risk to an IT network if one part of the system brings down a larger part of the entire system.

  2. Heartbeat packet: a soft detection technology that monitors the health of inline appliances. Read the heartbeat packet blog here.

  3. Critical link: the connection between two or more network devices or appliances that if the connection fails then the network is disrupted.

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