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TAP Into Technology

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[video] Observing The Impact Multiple Default Gateways With Wireshark

Posted by Tony Fortunato | 2/16/17 8:00 AM

I was speaking with a client the other day and they were asking me how Microsoft behaves if a device has two default gateways.

One thing I have to say about my job and clients, I always get interesting scenarios and questions to figure out.

He mentioned that they did some research online for a few hours and found many articles contradicted one another. They became frustrated and thought they would ask me. I searched around as well and understood their point.

I asked if they simply tried it in their lab, capture some packets while rebooting one of the routers to see what happens. I figure that it would take more time to setup the lab, than capturing and reviewing the packets.

In this video, I show you how I tested their question, how I used Wireshark and what I found out.

As I went through this example, I realized that I can go through the process of playing with metric settings but then remembered the client wanted to know how it behaved with default settings.  I also wondered if I left the test computer alone for a longer period, if it would eventually go back to the first router.  All things that I can go back and observe. That’s the nice thing of having a methodology, its easy to go back and try your ‘what if scenarios.’

I always recommend you start by documenting and understanding default behavior. Then you can confirm if any tuning parameters help.


Want more? Download the Network TAPs 101 - The Networking User Guide, where we discuss the connectivity strategy of the various TAP modes, as well as environmental considerations such as passive or active, and media conversion.

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Topics: Network TAPs, Network Visibility/Monitoring, Wireshark

Written by Tony Fortunato

Tony Fortunato is a Senior Network Performance Specialist with experience in design, implementation and troubleshooting networks since 1989. Tony will teach or troubleshoot on your live network as part of his customized onsite training service for your staff.