This is a well known issues called "Long Fat Pipe Network". There's many university papers about it and many tricks to get around it on software-based boxes. Adjusting your TCP window size was the best start, if it's set properlu. The basic formula is provided in this forum post : http://forums.whirlpool.net.au/archive/116165 Good luck ! 2011/6/28 Eugen Leitl <eugen@leitl.org>:
----- Forwarded message from William Salt <williamejsalt@googlemail.com> -----
From: William Salt <williamejsalt@googlemail.com> Date: Tue, 28 Jun 2011 08:03:25 +0100 To: support@pfsense.com Subject: [pfSense Support] Strange TCP connection behavior 2.0 RC2 (+3) Reply-To: support@pfsense.com
Hi All, For the last couple of months i have been pulling my hair out trying to solve this problem. We have a 1Gbps transatlantic link from the UK to the US, which has successfully passed the RFC2544 test.
At either end, we have a media converter, and a supermicro server with an intel quad port NIC running pfsense 2 (RC2 at one end RC3 at the other) and the IGB driver on the quad port.
We can pass 1gbps either way with UDP. However we are experiencing very strange issues with tcp connections.
With window scaling enabled, and a max socket buffer set to 16MB, we see no difference. Even disabling window scaling and setting the window to 16MB makes no difference.
Each TCP connection starts very slowly, and will max out at around 190mbps, taking nearly 2 minutes to climb to this speed before *plateauing*.
We have to initiate many (5+) connections to saturate the link with tcp connections with iperf.
Real world tests transferring files, max out at 100mbps, using multiple connections.
I have followed guides like this: http://www.psc.edu/networking/projects/tcptune/#FreeBSD
With no luck, and have tweaked, disabled, and enabled nearly every relevant sysctl parameter with no luck.
Can anyone shed some light on this?
I am now doubting the IGB driver, and am looking to swap out the cards as a last ditch effort. However, we have tried different hardware (L3 switches, media convertes + laptops etc), and the symptoms still persist... The only constant is freebsd 8.1 - pfsense (or 8.2 for our production systems). I have tried the freebsd net mailinglist, but im hoping you lot can help me!
Cheers in advance Will
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