I have experienced an issue that I believe lies with the GRO implementation in IGB 2.1.1.
The problem I see is that when GRO is enabled, TCP connections through the router are limited to approximately 300-500 kbps. If I disable GRO, I can get the full expected throughput. Regardless of offload settings, UDP connections are able to utilize the full expected bandwidth. I initially suspected that a firewall, or trafficshaping, issue was causing this problem, but ruled those out. Later, dumps of traffic turned up the fact that the machine believed it was receiving oversized (~2000 byte) packets, which led us to investigate the offload settings. The router device in question is based on the Intel 5520 Chipset, and is running kernel 2.6.29.6 (from kernel.org). I am using the igb 2.1.1 driver from intel.com. The card in question is an Intel Gigabit ET Quad Port, though I also see the issue on a LOM 82576 based NIC in the same box. Please let me know if there are any other details or information that might be of use in tracking this down. Thanks, Scott Silverman
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