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I'm managing an office network of about 20 computers, which all share a common ethernet switch (unmanaged), which is then connected to the ISP's cable modem/router combo.

Every now and then someone will run some scripts that spawn many threads that do heavy uploads and downloads, which seems to overwhelm the entire network, increasing latency for everyone to the point that the network is unusable.

What kind of switch or router should I be using, or what should my network setup be in order to avoid the situation where a single misbehaving machine can bring down our entire network?

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  • Does this only affect communication across the modem? Or is LAN traffic between machines slowed down as well?
    – rfc2460
    Feb 16, 2019 at 22:47
  • Only across the modem. Latency between machines within the network is fine.
    – user2468842
    Feb 18, 2019 at 1:05

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You don't say what model switch you are using but my guess is that it is a low-cost unmanaged switch. In the conditions you are describing one of two things can be happening when one of your systems goes highly active:

  1. You are saturating an link -- most likely the uplink to the internet but not necessarily -- and some packets from all systems aren't getting through.
  2. Packets are getting dropped because buffer space inside the switch is becoming exhausted. This is much less likely but needs to be considered if the first reason doesn't pan out.

Consider what happens if you have two servers connected to one switch with Gigabit Ethernet and the uplink you have to your ISP is 100Mbit. (or less). If each server may be trying to upload at 60Mbit/second at the same time something has to give. Ideally your switch will sense a buffer usage threshold being exceeded and start sending PAUSE frames back to the servers. Done right this kind of flow control is very effective. If you have a more complex network than what I described here it can make things worse.

You can get managed switches that give you the capability to manage buffers and bandwidth. You just have to pay more and learn to use them. Cisco, Dell, Delta, SMC, and Accton all have similar models in that range.

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  • Yes, it is a low-cost unmanaged switch.
    – user2468842
    Feb 18, 2019 at 1:08
  • This answer is incorrect in multiple ways. The reason for increased latency is that you have networking equipment with too much available memory for buffering packets. Most likely it's the modem. This problem is also known as buffer bloat. And using PAUSE frames is a terrible approach in this scenario as it would effectively slow the LAN down to match the internet speed. Then those servers become slow even for client on the LAN. A much better solution would be to have less memory in the modem such that packets are dropped sooner.
    – rfc2460
    Mar 8, 2019 at 23:08

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