Actually, with 10.4.8, SACK is there and enabled by default.
sysctl net.inet.tcp
You should see:
net.inet.tcp.sack: 1 net.inet.tcp.sack_maxholes: 128 net.inet.tcp.sack_globalmaxholes: 65536 net.inet.tcp.sack_globalholes: 0
-josh
On Oct 12, 2006, at 4:05 AM, Paolo Barbato wrote: Heiko,
I've recently faced a similar :-( problem with two Linux box. Problem arise with network stack, TCP Selective Acknowledgement Options SACK. High bandwidth links and large packets can emphasize bad behavior, and completely bocks specific protocols (for me was SMTP).
Try to turn off it on Solaris side, it's on by default.
Regards, Paolo.
At 12:37 +0200 12-10-2006, Heiko wrote: Hello,
I have a strange problem with TCP-communications, which is not directly related to developing software. I hope you forgive me, and can help me solve the issue, or point out OS parameters to workaround the problem (or even tune the OS' TCP-Stack to work properly :-) ).
Short description: The Mac is a OS X.4 client with 100MBit network connection (172.27.2.127), and the Sun is Solaris 10 AFP-Server (Ethershare) with a 1000MBit network connection (172.27.1.40). The problem only occurs while reading data from the Sun.
The Mac acknoledges data packets from the Sun very lazily, meaning the Sun sends up to 6 packets, the Mac ack's just one. This way the retransmission queue of the sun fills up with unacknoledged packets, forcing the Sun to throttle down.
Some packets later, the Sun only sends new packets if prior packets are acknoledged.
Now the Mac sends acks for more then one packet at a time (good thing), but delays the send about 500microseconds...this gets worse, until the delay is about 200ms (milliseconds!). As you can imagine, the throughput is near zero.
The whole description with TCP-dumps is available here:
http://www.wurst-wasser.net/Wurst-Wasser.net/Wiki-Uploads/BerlinTCPPerformanceProblem.pdf (10MB, good quality, better viewed in Preview than in Safari)
Has anyone heard of such a problem before?
It would be great if someone could point out possible causes, workarounds or even solutions.
Thank you!
-
Heiko
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