Monday, August 12, 2019

How much Layer 2 traffic is there on an average subnet?

Many years ago I worked for an ISP where we learned a lot more MAC addresses than you'd expect from a non-insignifigant number of our commercial customers. In the office we'd chuckle amongst ourselves that these companies clearly didn't know routing from switching.

I know in some odd cases you might need to have a subnet stretch across a private line, but we saw some extreme cases. There were internet circuits where we were learning two thousand MACs from a school district. There were private VPLS networks with hundreds of MACs. Etc.

I always wondered how much money these companies were probably wasting each month by needing a larger bandwidth pipe for all that L2 traffic. At $1k/mo even a 10% reduction could save a company $1,200 a year.

This question has been bugging me for years. I really need to set up Wireshark to do a test on my own subnet at work but I keep forgetting to. Maybe the responses from this post will remind me to. Even then, I'm not sure the traffic on our subnet will be average compared to other companies.

What's your experience with these things been?



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