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Network Flooding, Really?


Flooding is one of those networking topics that people always assume someone else will have.


Some of the common myths that involve flooding are; huge multipath networks, complicated load balancing configurations, and of course, x-file type problems.


Flooding can happen with the simplest devices or configurations. Let’s start with my simple but brief definition of flooding. When you see a lot of other device unicast addresses on your switch port, that’s flooding. Seeing the occasional flooded packet, isn’t that unusual, but if you see hundreds of unicast packets per second (that aren’t yours), you should investigate.


In my experience, any device that has 2 ports or more can cause or contribute to flooding. The most common example of flooding is when you have a host with 2 ethernet cards and a virtual ip/mac address. When the host communicates with you, it uses a real mac address, but when you talk back, you use a virtual mac address that the switch might not be aware of resulting in those return packets going to all switch ports.


Lately, I’ve seen cameras that have ethernet and WIFI connectivity to cause flooding, and not sure why. In this video, I will show you an example of this exact problem. the key troubleshooting tip is to start with interrogating your switch bridge forwarding table and compare it with the client or router arp table entries.


Tip when working with devices that support Ethernet and WIFI; in most cases, you use the WIFI for the initial configuration, then move the device to an Ethernet port. In these cases, I would recommend you clear the WIFI configuration details after you are certain the host is working properly with the wired connection.


Tony Fortunato

Sr Network Performance Specialist

The Technology Firm

Getting things to work better - bit by bit-


 

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