1gbit LFN WAN link - odd tcp behavior

[Scheffenegger, Richard]

What is the effective latency under load, and the packet loss
probability?

Just to add some more detail.

Richard Scheffenegger


> -----Original Message-----
> From: William Salt [mailto:williamejsalt at googlemail.com]
> Sent: Montag, 27. Juni 2011 12:15
> To: freebsd-net at freebsd.org
> Subject: 1gbit LFN WAN link - odd tcp behavior
> 
> 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 (freebsd 8.1) with the NIC
> running on
> the yandex IGB driver.
> 
> 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.
> 
> 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 (or 8.2 for production systems).
> 
> 
> Cheers in advance
> Will
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