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What does changing the number of packets sent during the initial congestion window to 10 have on LAN connections?


ip route change default via GATEWAY dev INTERFACE initcwnd 10 initrwnd 10

Is this advisable / inadvisable for high speed (1gbit) LAN connections?

Does this even have any affect for high speed LAN based connections?

What I mean by LAN connections is LAN Box <-> LAN Box. Communication that never sees 'the internet'.


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Since this is an optimization for high bandwidth, high latency connections, not much. – Michael Hampton Mar 22 '13 at 8:34

IW10 would always speed-up TCP connections during their slow-start phase (initially) but whether that would be noticeable in the context of how much data will be transmitted overall is another question.

IW10 is especially useful for short-lived TCP connections such as those opened by web browsers to load a web page. There may be much smaller benefits for long-lived connections transmitting a lot of data (such as transferring a big file using HTTP or FTP) although IW10, in comparison to IW3, would also help faster recovery in case of packet losses.

In your case the bandwidth is not a factor to consider. It's the latency that's important. Do a ping and check your round-trip time for the link, it would probably be 1ms or less. If so - there won't be any noticeable benefit unless you have many packet losses.

In general it depends on what you would use those TCP connections for. If you are trying to achieve some form of "real-time" communication between the two hosts and you will be sending more than a couple kilobytes of data (even though the connection enjoys high bandwidth and low latency) - a couple of milliseconds may count.

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IW10 can also increase retransmit rates due to it's more "bursty" behaviour. Google measured that increase being around 0.5%. – SaveTheRbtz Jul 24 '15 at 9:46

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