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3. My readings are inaccurate, how do I fix that?

The Analyzer reports the values that actually get to servers on the Internet, while tweaking programs like the Optimizer only change settings on your computer. There are a few possibilities to account for the differences:

First, make absolutely sure that the IP address displayed at the top of the Analyzer results page is yours. If it is not, then you are measuring the parameters of the connection between and the host that owns the displayed IP. That might be a web proxy, or a NAT device of some sort. Web proxy servers save your ISP's bandwidth, however they often have a negative impact on your Web experience. With Proxy enabled, you might experience problems accessing some Secure pages, as well as decreased performance.

To disable the Proxy server in Internet Explorer, go into Tools > Internet Options > Connections > LAN settings. In there, disable proxy, uncheck "Automatic settings" and try again.

If the IP address displayed by the Analyzer is yours, then the readings are most likely accurate. Complaining about them is equivalent to telling the manufacturer of your mirror that it is not reflecting your face accurately, because according to the description of your latest makeup kit, you should look much more attractive after applying it (my apologies to the male users, I couldn't come up with a more "manly" example :-) ).

There are still some routers and cable/dsl modems in use that modify the maximum packet size (MTU) regardless of Registry settings. If the Analyzer reports a smaller MTU and you're behind a router, you might want to try updating its firmware, or looking through its management interface for an MTU value.

It is also possible for some PPPoE, Proxy, or Firewall software on your computer might be changing some of the settings as well.

Note: The Analyzer does not look at Registry settings, it takes the values directly from the header information in TCP/IP packets, the same information your end advertises to other servers on the internet.

Note: Some ISPs automatically enable Proxy, regardless of your browser settings (if you have their custom software installed). As a workaround, you might have to uninstall such custom software and configure your connection manually.

Note: Don't forget to reboot after making changes to the Windows Registry, for those changes to take effect.

Note: In Windows 9x, if you have a number larger than 65535 for RWIN in the Registry, and the Analyzer always reads the RWIN value as 65535, you might need to install the MS Vtcp.386 Fix.

  User Reviews/Comments:
by Terry - 2006-02-01 20:39
Thanks for all this detailed information! Just one question: I've set my RWIN to be a multiple of my MSS*44, but after making that change the Analyzer says my RWIN is ~1kb greater than I set it to be. I'm behind a home gateway, so could that padding be NAT that the router tacks on? I can lower my comp setting to compensate for the padding, but I'm not sure which is more important: having the right ratio at my router or at my computer. Does the router acknowledge packet receipt, too? Thanks for your help.
by Philip - 2006-02-01 22:04
RWIN is not likely to be modified by a router. Make sure the Analyzer recognizes your right IP address, rather than a proxy server.
by casmgraph - 2006-06-05 22:41
server got os, ip, and other tidbits wrong, it got the browser rite even wit hide ip platinum, neway im running xp pro, is there even winnt 2000 5.1 or i halucinating on my monitor. server needs update or someone wormed my box
by gcnetspeed - 2006-08-27 19:07
Can anyone help the TCP Analyzer got my IP wrong but the TCP/IP Optimizer software has it correct
by TwinBit - 2006-10-15 20:30

registry entries shows: MTU 1492, tcp analyzer says MTU 1480! RWIN 1045440 is correct! (same value is in the registry) i'm not behind a router or firewall. (at test-time) the max. value via "ping -f -l" is 1452. Provider says: "1492 is the correct value"! so whats wrong?
by Rulatir - 2006-11-07 22:53
Linux user here. The test sees my RWIN as ridiculously small, 5888 bytes. Yes, bytes! Says it limits me to 29KB/s @ 200ms but I tend to have latencies of that order of magnitude and get full download speed ca 128KB/s. Something must be wrong with the RWIN detection.
by Philip - 2006-11-09 19:16
Rulatir, that's what your machine advertises as RWIN at the moment. Linux acts a bit differently, it opens the RWIN value as needed, rather than advertising what it is set at.
by davidows - 2007-11-24 09:39
I would give a 5 star rating for use with any version of Windows except Vista. This Analyzer and the TCP Optimizer are a waste of time for Windows Vista users. Rather than burying it in a FAQ that Vista is not fully supported, when the analyzer detects "Windows NT 6.0", why not eliminate the following red text warning in the Analyzer?

"RWIN is not fully optimized (even though it is a comparatively large number). The unscaled RWIN value is lower than it should be. Also, RWIN being close to and above 65535 does not justify the header overhead of enabling TCP 1323 Options. You might want to use one of the recommended RWIN values below."

Better yet, why not replace it with the following:

Unless you have disabled "TCP/IP Auto-Tuning" in Windows Vista, it is unnecessary to use TCP Analyzer or TCP Optimizer. Readings in the Analyzer will not be correct. Changes in the Optimizer will have no effect. For more information, refer to the Tweaking FAQ: "How to disable Windows Vista TCP/IP auto-tunning ?"
and this Microsoft TechNet article:
by mikel0230 - 2008-01-01 01:27
im just a new user. my tcp/ip analyzer shows wrong ip address.i want to speed up my smart bro connection. i've done all the process but it has no change and maybe because of my tcp/ip analyzer it wont read my ip address.please help me
by summerfairy - 2008-08-08 07:48
I have already disable the proxy settings in my browser (its now direct connection to internet) but the analyzer still cant get my IP address right.

How can i fix this? please help.
by Philip - 2008-08-08 11:17
Please post in our forums if you need help with the Analyzer not showing your correct IP address:
by anonymous - 2009-08-22 07:40
At your website I am getting MTU as 1420

My DLink GLB-502C adsl router GUI shows MTU as 1460

mturoute.exe( displays MTU as 1460 when I use it on my XP behind DLink router and any host including your website.

If anyone could tell me what is my actual MTU? TCP Analyzer Results
Tested on: 08.22.2009 07:39
IP address:
Client OS: Windows XP

TCP options string: 0204056401010402
MSS: 1380
MTU: 1420
TCP Window: 65535 (NOT multiple of MSS)
RWIN Scaling: 0 bits
Unscaled RWIN : 65535
Recommended RWINs: 63480, 126960, 253920, 507840, 1015680
BDP limit (200ms): 2621kbps (328KBytes/s)
BDP limit (500ms): 1049kbps (131KBytes/s)
MTU Discovery: ON
TTL: 104
Timestamps: OFF
IP ToS: 00100000 (32)
Precedence: 001 (priority)
Delay: 0 (normal delay)
Throughput: 0 (normal throughput)
Reliability: 0 (normal reliability)
Cost: 0 (normal cost)
Check bit: 0 (correct)
DiffServ: CS1 001000 (8) - class 1 (RFC 2474). Similar forwarding behavior to the ToS Precedence field.
by zary - 2009-10-06 18:41
Guys,I play online games,my latency is usually really low

it's a WIFI connection,I disabled the Windows Zero configuration,but I still get lag whenever there's a lot of action around,so I decided to change my TCP window size(RWIN)

but whatever I set my RWIN number to,I can't seem to get any changes in the analyzer(note: it shows a different IP than my router, most prolly an NAT device involved???)I'm not using any proxy...and I'm positive my firewall ain't doing it...

what should I do?!?
by zary - 2009-10-06 18:44
OS-XP anyway

I posted some stuff in that link!
by radiolondra - 2021-04-29 01:59
I'm using the latest version (2021) and it seems ther's no different version for 32/64 bits.
On 64bits PCs, TCPOptimizer reads/writes the HKLM/Software/Wow6432Node registry tree.
This cause the read of wrong or inexistent registry keys and values, and incorrectly showing defaults. And can create a mess writing new values.
This happens, for example, for "NetworkThrottlingIndex" and "SystemResponsiveness" (HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Multimedia\SystemProfile), inexistent in Wow6432Node, and for other keys too.
by Philip - 2021-04-29 08:55
Please use our forums for questions and reporting issues.

This FAQ is about the Analyzer, not the Optimizer software. Still, the Optimizer reads settings using PowerShell cmdlets mostly, if it is reading in the 64-bit hive that's something Microsoft should fix, but we'd still check. The Optimizer doesn't write to WOW6432Node , you can see where it writes when you hit the "Apply changes" button. Again, please use the forums for further issues with it, thanks.
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