From: Rick Jones <rick.jones2@hp•com>
To: netdev@vger•kernel.org
Subject: A SACK block to the left of the ACK? (with ptr to raw trace)
Date: Fri, 09 May 2014 10:34:24 -0700 [thread overview]
Message-ID: <536D11A0.6050400@hp.com> (raw)
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
next reply other threads:[~2014-05-09 17:34 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-09 17:34 Rick Jones [this message]
2014-05-09 18:21 ` A SACK block to the left of the ACK? (with ptr to raw trace) John Heffner
2014-05-09 18:25 ` Rick Jones
2014-05-09 19:18 ` David Miller
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