From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rick Jones Subject: Re: A SACK block to the left of the ACK? (with ptr to raw trace) Date: Fri, 09 May 2014 11:25:11 -0700 Message-ID: <536D1D87.3060706@hp.com> References: <536D11A0.6050400@hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Netdev To: John Heffner Return-path: Received: from g4t3425.houston.hp.com ([15.201.208.53]:38178 "EHLO g4t3425.houston.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756553AbaEISZM (ORCPT ); Fri, 9 May 2014 14:25:12 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: On 05/09/2014 11:21 AM, John Heffner wrote: > I didn't actually look at the trace, but offhand this sounds like > D-SACK. (http://www.ietf.org/rfc/rfc2883.txt) Thanks for the gentle tap with the clue-bat :) rick > -John > > > On Fri, May 9, 2014 at 1:34 PM, Rick Jones wrote: >> Hi - >> >> As part of looking at a customer issue, I've been running some netperf >> TCP_RR between a pair of instances running 3.2.0 with whatever stuff >> Canonical have backported into their -60 version. While looking at packet >> traces I've seen the following odd SACK: >> >> 08:14:40.329583 IP 15.126.222.122.48130 > 10.0.0.3.12345: Flags [.], ack >> 63734, win 457, options [nop,nop,TS val 14282026 ecr 14255813,nop,nop,sack 1 >> {63716:63717}], length 0 >> >> I don't think that this "to the left of the ACK" SACK block actually caused >> anything heinous to happen but it does look odd and so I thought I might >> mention it to see if anyone else has seen it or if perhaps it is a known >> issue fixed in a later kernel. The full tcpdump from one side is up at: >> >> ftp://ftp.netperf.org/rr_16.pcap.gz >> >> The netperf running was: >> >> ubuntu@zpet-netperf-east-1-vm01:~$ netperf -l 60 -H zPet_NetPerf-East-2-vm01 >> -t TCP_RR -- -b 16 -D -P ,12345 >> >> So TCP_NODELAY was set (-D), and there were upwards of 17 segments in flight >> at any one time (-b 16 - 16 added to the default of one). >> >> The trace was taken at zPet_NetPerf-East-2-vm01. As you might have guessed >> there is NAT involved - in both directions actually. The node(s) on which >> this NAT is happening are running a 3.5.0-44 kernel. >> >> Here is one being sent from the side where the trace was being taken: >> >> 08:15:01.137718 IP 10.0.0.3.12345 > 15.126.222.122.48130: Flags [.], ack >> 218871, win 453, options [nop,nop,TS val 14261016 ecr 14287228,nop,nop,sack >> 1 {218854:218855}], length 0 >> >> Which I suppose rules-out some odd NAT bug as the source of the "to the left >> of the ACK" SACKs since that was captured pre-NAT. >> >> happy benchmarking, >> >> rick jones >> -- >> To unsubscribe from this list: send the line "unsubscribe netdev" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >