TCP and WAN issue

Leo Bicknell bicknell at
Wed Mar 28 01:44:05 UTC 2007

In a message written on Tue, Mar 27, 2007 at 02:41:13PM -0700, Philip Lavine wrote:
> This is the exact issue. I can only get between 5-7 Mbps. So the
> question is really what incremental performance gain do WAN
> accelerators/optimizers offer? Can registry/OS tweaks really make
> a significant difference because so far with all the "speed
> enhancements" I have deployed to the registry based on the some of
> the aforementioned sites I have seen no improvement.

In short, yes.

Working for an ISP with colos on both coasts I helped customers on
numerous occasions "tune" their operating system.  A plain jane
desktop from choose your favorite vendor today will do ~300-~500Mbps/sec
of FTP with only minor tuning assuming you have good disks (e.g.
not a laptop).  Most servers can be easily tuned to chew a full

TCP Window Scale, Selective Acknowledgement, and a "TCP Send" and
"TCP Receive" buffers that are big enough to handle your bandwidth*delay
product (*2 for a good margin) are all that's required.  Jumbo
frames are not, and in fact make little difference.  All of the TCP
limits are 100% the same with Jumbo frames, and most NIC's generate
roughly the same number of Interrupts with Jumbo frames enabled.
You're saving a little bit of IP processing overhead on the end
hosts, but I doubt you'll measure it.

Wan optimizers are extremely complex points of failure that generally
mess with the protocol in ways that are extremely dangerous, they
should only be used if you don't have direct access to the end boxes
to fix them.

Google can turn up 50 write ups on how to tune your settings better than
I could ever write here.

       Leo Bicknell - bicknell at - CCIE 3440
        PGP keys at
Read TMBG List - tmbg-list-request at,
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