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iMacPro - Losing packets to Switch CSS326-24G-2S+

Posted: Fri Jun 26, 2020 9:13 am
by phuketmymac
I have an issue with an iMac Pro losing network packets to the switch on a 10GbE small network.
The config is as follow:

1) iMacPro 10GbE port -> Cat6a cable (cable matters 10m) -> Mikrotik S+RJ10 -> Mikrotik Switch CSS326-24G-2S+

2) Mikrotik Switch CSS326-24G-2S+ -> Cisco type SFP+ connector (possibly fake one) -> SFP+ cable 3m -> HP 560SFP+ Intel X520 -> HP Proliant ML350p (FreeNAS Server)

The problem happens between the iMacPro and the Switch only.
Pings are being dropped from the iMac and so the connection is dropping in the Finder and Final Cut Pro, ONLY when we push the network by doing some work in Final Cut Pro.
At first, connection works fine, we can access the Server using the Finder, mount the shares, ping the Server, etc...
Once we load Final Cut Pro and do some modifications which involved loading big files from the Server then we start to see FCPX freeze and dropped pings.
If I ping the Server or the switch from the Wi-Fi using another Mac, I have no issues but I will get dropped packets to the iMacPro.
So it's confirmed to be only between the iMacPro and the Swtich.

The iMac Pro was on macOS Mojave (10.14) at the time of the installation.
Everything was working fine back then, no lag when using the 10GbE interface while scrolling through 4K previews in FCPX.
One day, he did have to move place and moved the equipment as well.
Apparently, since then the problem started to happen.
So I thought cable, damaged equipment or possibly a macOS software update which broke something.

We did try another cable Cat6 (not 6a though), same thing.
We did replace the switch with another one (same model), same thing.
We did try another port on the switch (in gigabit only), same thing.
We did try an Ethernet adapter to USB-C in Gigabit only, same thing.

Ethernet speed is set to automatic in the preferences and will sometimes remain in 10GbE while getting dropped packets or will drop to Gigabit.
We also saw the Ethernet link dropped to 100Mb/s once.

I would say that the remaining part is the iMac itself but since we've tried an ethernet adapter, I am confused now.
I have ordered a Cat7 cable which should arrive soon but I am wondering if the setup as it is with the Mikrotik SFP+ is powerful enough to support the 10GbE with the iMac if the switch with the Ethernet adapter is a wrong choice.

Any hint would be appreciated.