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I'm trying to flow data via UDP on two ports of a Netgear GS110TP switch, running the latest available firmware (5.4.2.9). However, I'm experiencing a small amount of packet loss, something like 0.2%. This is impacting my application, which needs high reliability UDP data transfer.

I have two Linux machines connected directly to the switch. These two machines are completely different from a hardware and software perspective. If I remove the Netgear switch and replace it with a dumb 100Mbit hub, I see no packet loss between the two machines. Sadly, I need to use the Netgear switch, so I need to figure out what is going wrong with it.

I'm using iperf in the following manner to check for packet loss:

Machine #1 is running iperf -u -s

Machine #2 is running iperf -c [machine #1 ip] -u -r -b 20M -t 10

I would expect that, given the tiny amount of data compared to the available bandwidth that all the packets would flow successfully. Even at 5Mbit, I still see a small amount of loss. I've also tried forcing the port speeds to 100Mbit to see if that helps, which it does not.

Checking the switch logs, I see the counts for

  • Total Packets Received with MAC Errors
  • Rx FCS Errors
  • Alignment Errors

... are all non-zero. The "MAC Errors" in particular seems to correlate relatively well with the results of iperf.

I'm a bit unfamiliar with this switch's configuration (and "high-end" switching in general) so I imagine I have something misconfigured somewhere.

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up vote 2 down vote accepted

Rx FCS errors are checksum errors for the frames received. They tend to occur due to faulty cabling, electro-magnetic interference or faulty interfaces. Alignment errors are basically in the same failure class indicating incomplete bytes received. You might want to change cabling runs, swap switch ports and / or replace the interfaces on your hosts to rule out the possible causes.

Re: "high-end" switching: The GS110 is the "smart managed" line of a cheapo network equipment re-labeler. It is as low-end as it gets in a professional environment. Personally, I would swap it out with no questions asked. Especially since in your case the inherent need to connect two Linux machines via a PoE switch is not apparent.

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I'd be willing to bet EMI is to blame - we are using the PoE features, and I've seen EMI issues with other interfaces (ie, audio) as a result of the PoE usage. –  jldeon Oct 14 '13 at 19:09
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