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Date: Mon, 03 Mar 2014 16:29:09 -0800 From: Rick Jones <rick.jones2@...com> To: netdev@...r.kernel.org Subject: TCP being hoodwinked into spurious retransmissions by lack of timestamps? I've been looking at some packet traces of an application looking to upload a Large Quantity (tm) of data to a server across the Big Bad Internet (tm). They've been Linux senders, and the destination while supporting SACK and window scaling does not support TCP timestamps. (TCP timestamp support was requested of the supplier of said server many many months ago now.) This destination system has been issuing RSTs at seemingly random points in the middle of a large fraction of the attempted transfers. In looking at the traces, they all seem to be variations on the theme of what is shown by: ftp://netperf.org/retrans_question/for_netdev.png which is a passing of ftp://netperf.org/retrans_question/for_netdev.pcap through tcptrace -nG and zoomed-in to the end. I've seen this with a 3.2.0 kernel as the sender, have reports of it happening with whatever is in Fedora Core 20, and the traces above are from a 3.11.0 kernel as the sender. The large quantity of (likely) unnecessary retransmissions shouldn't be triggering a RST by the receiver, but the failures consistently show that and I was wondering if the (spurious) retransmissions were perhaps "encouraged" (so to speak) by the lack of TCP Timestamps. happy benchmarking, rick jones -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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