Jumbo frames

Jim Shankland nanog at shankland.org
Tue Mar 27 23:28:27 UTC 2007

<michael.dillon at bt.com> writes:

> [...]
> if there are several factors that will contribute to solving the
> problem, I think that you get better results if you attack all of them
> in parallel.

Well, I guess; except that "only buy IP network access from a service
provider who supports jumbo MTUs end-to-end through their network"
may be a much bigger task than tuning your TCP stack.

Jumbo frames seem to help a lot when trying to max out a 10 GbE link,
which is what the Internet land speed record guys have been doing.
At 45 Mb/s, I'd be very surprised if it bought you more than 2-4%
in additional throughput.  It's worth a shot, I suppose, if the
network infrastructure supports it.

On a coast-to-coast DS-3, a TCP stack that's correctly tuned for a
high bandwidth-delay product environment, on the other hand, is
likely to outperform an untuned stack by a factor of 10 or so
in bulk transport over a single TCP session.  (Though, as somebody
pointed out, tuning may have to occur all the way up the application
stack; there are, e.g., ssh patches out there for high-BDP environments.)

So I guess, sure, try anything you can; but I know what I'd try
first :-).

Jim Shankland

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