MTU keeps changing...How to I lock it?

Capitalizt · Post by **Capitalizt** » Tue Sep 21, 2004 10:54 pm

I'm on dialup and would like to lock my MTU at 1450. When I run MTU tests, the MTU gets fragmented at anything over 1450.

The MTU is set at 1450 in the TCP Optimizer program, yet when I do the TCP Analyzer scan, I get a result of 1500.

I tried going into the registry manually under TCP/Parameters and added an MTU value of 1450. I also turned PMTU discovery OFF in hopes that it would use the 1450 value, but it just won't stick!

Advice?

mccoffee · Post by **mccoffee** » Wed Sep 22, 2004 9:37 am

What windows version you have??

Capitalizt · Post by **Capitalizt** » Wed Sep 22, 2004 3:07 pm

Windows XP Home SP2
standard Conextant 56k dialup

mccoffee · Post by **mccoffee** » Wed Sep 22, 2004 3:42 pm

take a tcpip analyzer let me see your settings

Capitalizt · Post by **Capitalizt** » Wed Sep 22, 2004 4:29 pm

here ya go

Browser/OS = Mozilla/5.0 (Windows; U; Windows NT 5.1; rv:1.7.3) Gecko/20040913 Firefox/0.10
Notes: Read the Analyzer FAQ if the above is not your IP address.
TCP options string = 020405b401010402
MTU = 1500
MTU is fully optimized for broadband.
MSS = 1460
Maximum useful data in each packet = 1460, which equals MSS.
Default Receive Window (RWIN) = 8760
RWIN Scaling (RFC1323) = 0 bits
Unscaled Receive Window = 8760

RWIN is a multiple of MSS
Other values for RWIN that might work well with your current MTU/MSS:
513920 (MSS x 44 * scale factor of 8)
256960 (MSS x 44 * scale factor of 4)
128480 (MSS x 44 * scale factor of 2)
64240 (MSS x 44)
bandwidth * delay product (Note this is not a speed test):

Your RcvWindow limits you to: 350.4 kbps (43.8 KBytes/s) @ 200ms
Your RcvWindow limits you to: 140.16 kbps (17.52 KBytes/s) @ 500ms
Consider increasing your RWIN value to optimize TCP/IP for broadband.
MTU Discovery (RFC1191) = OFF
Time to live left = 116 hops

TTL value is ok.
Timestamps (RFC1323) = OFF
Selective Acknowledgements (RFC2018) = ON
IP type of service field (RFC1349) = 10000000

Precedence (priority) = 000 (routine)
Delay = 0 (normal delay)
Throughput = 0 (normal throughput)
Reliability = 0 (normal reliability)
Cost = 0 (normal cost)

I'm also trying to set the default receive window to 8460, which would be a multiple of 1410 X 6 rather than 1460 X 6 (8760).

It resets every time I take the analyzer, even though the cablenut and TCP Optimizer settings show otherwise...

MadDoctor · Post by **MadDoctor** » Wed Sep 22, 2004 6:02 pm

Have you used other tweaking tools in the past? One of those "other tools" still might be installed and is over-riding the settings of cablenut and/or the TCP Optimizer. A little more history of what you've done to that PC would be nice.

Capitalizt · Post by **Capitalizt** » Wed Sep 22, 2004 6:20 pm

nope, did a fresh install about a week ago...I do have AOL installed on my PC by default, but I have never used it. Could deleting the AOL registry entries possibly help?

MadDoctor · Post by **MadDoctor** » Wed Sep 22, 2004 10:49 pm

https://www.speedguide.net/forums/ ... hlight=AOL

chpalmer · Post by **chpalmer** » Wed Sep 22, 2004 11:10 pm

The AOL install program is there by default but doesnt install unless you double click.

So if you got rid of AOL before the format, then theres help for you.

Also - Your winmodem can be a resource hog "Conextant 56k dialup"

Had one, it was!