Re: anybody tried this?

Brian Godette (bgodette@idcomm.com)
Thu, 25 Jun 1998 10:48:29 -0600


At 11:58 PM 6/24/98 -0400, Danny Morris wrote:
>Hiya,
> Far be it for me to say anything to contradict Jason, but from my
>understanding, it has alot to do with the max trans. rate that your IP
>handles. MaxMTU lets you change and test different packet (it is made for
>ppl that dont understand all of this stuff, like me :-) sizes and shows
>weather or not they where fragmented when you ping a server. The standard is
>MTU=576, here anyway, when I tried higher it would fragment the packets

Having an MTU of 576 on ISP equipment would be *really* odd unless they're
connected to the net thru an old unix box using slip connections.... The
smallest max (almost always the default as well) MTU size you'll see on any
hardware that's likely to be used is 1500 (10bT ethernet), just about every
other LAN/WAN transport medium has a larger max MTU size than ethernet. If
you're getting "Packet needs to be fragmented but DF set." from a 'ping -f
-l 1472 some.local.isp.system.com' under 95/98/NT it's because you still
have the MTU size set below 1500 for the PPP interface.

>which, correct me here Jason, could just slow down your transfer rate. I
>downloaded a file today at 6.2 kbps, not bad for a dial up conn. As for the
>cameras (CU), Im not sure this would help, but it seems like it would.
Streak ?

6.2k on what file, how big, and at what connect rate? Without all three
it's meaningless, I've personally shoved a few meg of html (object listing
out of Squid's cachemgr.cgi) at 80Kbytes/sec down a 26400 link thanks to
inband packet compression, which just demonstrates the importance of using
zip/gzip'd files for transfer rate tests.

In anycase setting the MTU size to smaller than 1500 will have the opposite
effect that's desired where CU is concerned. If your objective is to make
things like telnet/real-time ICQ chat window/MUDs/MOOs be more responsive
while downloading some big honkin' file (such as WP ECU 3.1.1) then setting
it smaller will do that. Of course changes to MTU sizes will at a minimum
require reconnecting to your ISP and possibly even rebooting before that.