Proxmox fluctuation in Network Speed via Iperf

[Gilgamesh]

I got an issue since a while that the network connection speed drops on my Proxmox. (I check it with Iperf3)
I have an 2.5 Gbit connection but sometimes the speed drops to 1 Gbit or sometimes even 100 Mbit. The clue is. I get this resolved 99% of the time when I change the MTU in the GUI from e.g. 6000 to 6001 or 5999. And apply configuration. Until let's say few hours later or a day later its slow again and I need to fix again.

Did anyone experience something like that? Or heard of this Problem before.

 

[aaron]

I would use iperf instead of iperf3 because the latter is always single threaded, while the former will be multithreaded when the -P parameter is used to run multiple parallel connections.

On the other hand, that behaviour does sound fishy. Did you see what ethtool {nic} shows? Maybe it negotiated to a slower bandwidth? That could be due to broken or bad cables for example. Changing the network settings could cause the NIC to be taken down and up again, upon which it renegotiates the speed.

 

[Gilgamesh]

Thank you for your answer. I tried ethool now and took a screenshot. I take another one when the speed drops again and will compare results and probably post it here.

 

[Gilgamesh]

I would use iperf instead of iperf3 because the latter is always single threaded, while the former will be multithreaded when the -P parameter is used to run multiple parallel connections.

On the other hand, that behaviour does sound fishy. Did you see what ethtool {nic} shows? Maybe it negotiated to a slower bandwidth? That could be due to broken or bad cables for example. Changing the network settings could cause the NIC to be taken down and up again, upon which it renegotiates the speed.

See attached normal speed 2.5 Gbit and one from today when the speed was down to 100 Mbit. Link partner seems to communicate different speed for what reason ever. I changed a few cables already for different ones a few days ago.

 

[aaron]

So, for whatever reason, the "Speed" gets negotiated down to 100 Mbit/s. If you tried a few cables, it might be that they are not of good enough quality, CAT 5 instead of CAT 6? And/or too long?

 

[_gabriel]

iirc, there is a report with Realtek nic + vlan + mtu.
I don't remember the topic.

 

[Gilgamesh]

So, for whatever reason, the "Speed" gets negotiated down to 100 Mbit/s. If you tried a few cables, it might be that they are not of good enough quality, CAT 5 instead of CAT 6? And/or too long?

Cables are CAT6 or higher. Was actually running good the last 4 days without Problems. It can be long. The server is in my Garage. But than again, was running good for 4 days straight. I added just recently next to the 2x 2.5 Gb RJ45 PCIe Card one 10Gb SFP+ PCIe Card. I gonna try to switch over to that as main NIC. Still need to find out how to do that. Because my knowledge is limited and I´m afraid that I don't reach the server later.

I have it running as Linux Bridge at the Moment for only my TrueNAS VM and just checked the speed with iperf and it's good. 2.13 Gbits/sec (switch is only connected to 2.5 Gb at the moment that's why not faster).

 

[Gilgamesh]

Problem still the same. Even on a different network adapter. But now I even don't get it resolved by changing MTU settings. Reboot of Proxmox required. I getting crazy with this and for me it doesn't make sense.

 

[Gilgamesh]

I would use iperf instead of iperf3 because the latter is always single threaded, while the former will be multithreaded when the -P parameter is used to run multiple parallel connections.

On the other hand, that behaviour does sound fishy. Did you see what ethtool {nic} shows? Maybe it negotiated to a slower bandwidth? That could be due to broken or bad cables for example. Changing the network settings could cause the NIC to be taken down and up again, upon which it renegotiates the speed.

I managed to find one bad cable and since I changed it I have stable speeds. Thank you. Problem seemed to be solved.