MTU problem DSL/CABLE Router - Firwall upgrade

Archived from groups: comp.security.firewalls (More info?)

This is a Good advice for other newbies like me trying to tweak a new
Broadband Router/Firewall

I noticed a Major Bandwith performance decrease right after I upgraded my
good old Linksys BEFR41 to a Netgear FR114P.

It took me couple days to find out it was only a bad MTU setting.

Make sure you set the router/firewall MTU to its optimal value.

I found a good article which explain out to do it.

http://www.dslreports.com/faq/5793

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Archived from groups: comp.security.firewalls (More info?)

On 28-Aug-2005, Volker Birk <bumens@dingens.org> wrote:

> Optimal? You mean, small enough, because some providers have such
> problems.

Optimal means not too small and not too large. The default MTU at 1500 in
the Netgear was too large.
Optimal value in my case is 1456 according to the test describe in the link
above.

"Setting your computer's MTU value too low would make downloading less
efficient because a greater percentage of the packet is taken up by the
packet header which contains a variety of information about the packet,
source, and destination. However, setting the MTU too high can also decrease
efficiency. Other computers on the Internet might not be able to handle MTU
values of a certain size. If you set your computer's MTU value too high,
some computers along the delivery path would be required to break these
packets into smaller pieces before accepting them and passing them to the
next computer. This "Stop. Break. Go." processing of packets can
dramatically slow down data transfers."

Archived from groups: comp.security.firewalls (More info?)

Ok... we are playing on words now

For my setup, 1456 is the largest MTU I can set without having fragmented
packets.

Also, I started to notice decreased performance under 1400.

According to what I've read, the optimal value is the largest MTU that
doesn't cause packet fragmentation.
So is it really a compromize?

Cheers,
C++.