Whole network lags when one PC downloads anything

[brett1324]

I have multiple PC's on my network connected through LAN. Lets say PC1, PC2, and PC3.

When PC1 and PC2 download or stream anything, it is not noticed over the network by anyone else. No performance lost. When PC3 trys to download anything larger than 1gb, the other two PC's connections drastically drop to snails speed. QOS has been enabled to stop any one device taking all the bandwidth. Whats even weirder is PC3 also downloads everything at about 1/4th the speed as any other PC.

Any ideas what could be causing these issues?

 

[anotherdrew]

A dirty little secret. QoS is for upload traffic ... it has little effect on download traffic (generally speaking ... there are exceptions).

On to your problem. I'm not surprised that the download speed is lower. I except that what is happening is a lot of errors that required the retransmitting of data. This is most likely due to a faulty cable, but it could also be a faulty port or Ethernet adapter. Another possibility is a virus or something that is uploading data when you download (less likely, but a virus scan is easy). The other possibility is a weird configuration or driver issue, but start with the simple stuff.

 

[failboat]

standard networking is fifo. first come first serve. fq_codel is round robin and it keeps your latency minimal on small flows.
sharing download bandwidth can be tricky because there are many factors. tuning can get very complicated. fq_codel out of box is pretty nice though.

what's your internet speed and is the quality pretty consistent @ 90% of your bandwidth, no huge dips downwards or upwards on dslreports test? What QoS are you running now on what router? describe the traffic shaping you would like, does latency matter?
Not many implementations can run over 100Mbs. EdgeRouter X is $50 and is a great option for <100Mbs. <10Mbs are even harder to fine tune.

https://www.bufferbloat.net/projects/codel/wiki/
http://burntchrome.blogspot.com/2014/05/fixing-bufferbloat-on-comcasts-blast.html
https://www.youtube.com/watch?v=o-g2P3R84dw