consider the following setup:
A host on local Lan with 10GB networking, connected to a managed layer2 10GBE switch, which is connected using a 1GB link to a router. The Router is conneced to the internet using a 1G/1G symmetric fiber.
Now, I do a speed test or a test using iperf3 to measure the upload to a host in the internet. I get a result of about 50Mbit/s (upstream speed).
I set the link speed of the PCs network card to 1GB. Again do the speed test, I geht about 900Mbit/s upstream speed.
Any other host in the lan which is connected using a 1G connection will have speedtest results which match the advertised speed of the internet.
I recheck the problem using a different physical PC, using a network card of a different manufacturer. No change.
I do all the tweaks I know (disabling VMQ, large send file offload, RSC etc. etc.). No change
As a side note: I get full speed test results in the internal lan, regardless if I test 10GB to 10GB or 10GB to 1GB or 1GB to 10GB hosts. Also full speed in the internal lan If I run tests at the same time on multiple hosts.
Now, finally I change the internal lan link to the Router from 1GB to 10GB. Problem is gone. 900Mbit/s upload speed from any host.
Even If I kinda have solved this problem, I am thinking about reasons why this happens. Shouldnt the 10GB/1GB switch I use or finally the switch of the Router do their work using buffers and handshake to make this problem impossible to appear?
The speed of the internet is of course slower the the lan speed, but this is normal.
Who is to blame for this problem?
Me? because this is common knowledge? I searched and found a few topics but none of these seemed to have a real answer.
The switch? or the switch of the router? Or this is just a firmware problem of one of the involved devices?