Cap on network speed in CURRENT?

Brooks Davis brooks at
Tue Jun 1 17:03:06 PDT 2004

On Tue, Jun 01, 2004 at 03:38:18PM -0700, Luke wrote:
> I've got a 100Mbps LAN with ethernet cards that should be capable of using 
> it, yet the highest transfer rates I seem to be able to get out of my 
> FreeBSD box are 260KB/s receiving and 341KB/s sending with around 200KB/s 
> being more normal.
> I realize that there are hundreds of factors that could be influencing 
> this, but I came across this recent article that made me wonder if this is 
> some kind of hardcoded limit:
> Is this article saying that my network speed is limited by a small 
> static TCP buffer size?  If so, is there some way that I can increase that 
> buffer size to improve performance?  The primary function of this machine 
> is to move large amounts of data across my network, so I'm willing to 
> experiment with increasing the buffer size if it's not too difficult.

On a LAN, buffer size has minimal effect except at very high speeds.
Without tuning, two 5.x boxes with gigabit interfaces connected to a
Cisco 6513 switch (one 5/10/04 and one 2/20/04) reached 187Mbps in
iperf.  You're problems symptoms sound like duplex mismatch or bad
hardware to me.

-- Brooks

Any statement of the form "X is the one, true Y" is FALSE.
PGP fingerprint 655D 519C 26A7 82E7 2529  9BF0 5D8E 8BE9 F238 1AD4
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