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Re: Why is my gigabit ethernet so slow?



gson%gson.org@localhost (Andreas Gustafsson) writes:

> Steven Bellovin wrote:
>> > I wonder if it would make sense for the kernel to keep a list of
>> > networks to disable SACK on, or look at TTL values to determine that.
>> 
>> In theory, one should never have to disable it explicitly; its use
>> is negotiated.  But there's no particular harm to using if if both
>> sides support it; it's just that it's not likely to help much.
>
> In my experience, on NetBSD, SACK does cause harm, by breaking
> TCP Fast Retransmit.  See the discussion on tech-net in 2008:
>
>   http://mail-index.netbsd.org/tech-net/2008/01/28/msg000168.html

So probably our SACK implementation should get fixed, unless this is
really intrinsic in the spec (which seems hard to believe).

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