Date: Wed, 6 Dec 2006 18:45:19 -0500 From: Bill Moran <wmoran@collaborativefusion.com> To: freebsd@sopwith.solgatos.com Cc: freebsd-questions@freebsd.org Subject: Re: TCP parameters and interpreting tcpdump output Message-ID: <20061206184519.f3ceefb5.wmoran@collaborativefusion.com> In-Reply-To: <200612062246.WAA17265@sopwith.solgatos.com> References: <200612062246.WAA17265@sopwith.solgatos.com>
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Dieter <freebsd@sopwith.solgatos.com> wrote: > > I found a couple more things that don't look right. > > 000017 IP bsd.63743 > src.65001: . ack 52 win 65535 > 000107 IP bsd.63743 > src.65001: . ack 52 win 65535 > 000012 IP bsd.63743 > src.65001: F 52:52(0) ack 52 win 65535 > 000005 IP bsd.63743 > src.65001: F 52:52(0) ack 52 win 65535 > 000172 IP src.65001 > bsd.63743: . ack 53 win 4096 > 000004 IP src.65001 > bsd.63743: F 52:52(0) ack 53 win 4096 > 000003 IP src.65001 > bsd.63743: . ack 53 win 4096 > 000016 IP bsd.63743 > src.65001: . ack 52 win 65535 > 000011 IP bsd.63743 > src.65001: . ack 53 win 112 <------ why does the window suddenly shrink? > 002366 IP src.rfe > bsd.12340: P 1:1317(1316) ack 1 win 4096 > 099554 IP bsd.12340 > src.rfe: . ack 1317 win 65535 <------ why does it take 99.5 millisec to ack? > > The ack time is normally 12 or 13 microseconds, which seems to be okay. > But 99.5 milliseconds is *way* too slow, data will be lost. > > Is TCP sitting around waiting for a second packet, so that > it can be "efficient" and ack two packets at once? sysctl -d net.inet.tcp.delayed_ack net.inet.tcp.delayed_ack: Delay ACK to try and piggyback it onto a data packet That sysctl will turn it off for all network connections on the system. You can also set it on a per-socket basis using setsockopt and the TCP_NODELAY option. Some google searches on TCP_NODELAY will provide interesting technical details. -Bill
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