Cant set MTU to 1492!!!

[crazyjw1971]

I've been trying to set this damn MTU to 1492, but every site I go to reports back 1400. WTF? Ive uninstalled and reinstalled my NIC card, Ive reinstalled RASPPPoE, I've applied patches, etc. What now?

Please help...

[EvilAjax]

What Operating System are you running and are you using a router?

[crazyjw1971]

Windows 2000 Pro. No router.

I went into Regedit and the current value for MTU is 1492, but when I use Speedguide's TCP/IP analyzer or DSLReports' Tweak tester, they report back an MTU value of 1400!

WTF?

[crazyjw1971]

TCP options string = 02040550010303000101080a000000000000000001010402

MTU = 1400
MTU is not fully optimized for broadband. Consider increasing your MTU to 1500 for better throughput.

MSS = 1360
Maximum useful data in each packet = 1348, which is less than MSS because of Timestamps, or other TCP/IP options used.
MSS is not fully optimized for broadband (although it might work well for slower connections). Consider increasing your MTU value.

Default Receive Window (RWIN) = 17424
RWIN Scaling (RFC1323) = 0 bits
Unscaled Receive Window = 17424
For optimum performance, consider changing RWIN to a multiple of MSS.
Other values for RWIN that might work well with your current MTU/MSS:
522240 (MSS x 48 * scale factor of 8)
261120 (MSS x 48 * scale factor of 4)
130560 (MSS x 48 * scale factor of 2)
65280 (MSS x 48)

bandwidth * delay product:
Your RcvWindow limits you to: 696.96 kbps (87.12 KBytes/s) @ 200ms
Your RcvWindow limits you to: 278.784 kbps (34.848 KBytes/s) @ 500ms
Consider increasing your RWIN value to optimize TCP/IP for broadband.

MTU Discovery (RFC1191) = OFF

Time to live left = 58 hops
TTL value is ok.

Timestamps (RFC1323) = ON
Note: Timestamps add 12 bytes to the TCP header of each packet, reducing the space available for useful data.

Selective Acknowledgements (RFC2018) = ON

IP type of service field (RFC1349)= 00000000

____________________________________________________

I keep trying to change MTU and this is what I keep seeing.

DAMMIT!

[EvilAjax]

I see your problem.

EnablePMTUDiscovery

When set to 1 (True), TCP attempts to discover MTU automatically over the path to a remote host. Setting this parameter to 0 causes MTU to default to 576 which reduces overall performance over high speed connections. Note that this setting is different than our Windows 9x recommendation.

HKLM\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\
EnablePMTUDiscovery="1" (DWORD - boolean, valid settings are 0-->False and 1-->True. Many connections perform better with this entry at 1, however, if you prefer to set your upstream to send fixed 1500 packets, you might want to use 0 instead). When set at 1, establishing connections and initial transfer speed might slow down a bit, however you will get better throughput if somewhere in the path large packets need to be fragmented.

Let me know if this works.

[EvilAjax]

MTU Discovery (RFC1191) = OFF
That's what gave it away. Read the above post and you should be fixed.

[TheMyth]

And if turning on MTU Discovery doesn't work (like in my case when i used win2k), this will: (i'm assuming your still using RASPPPOE).

search for 'RMSPPPOE' in regedit (sorry if thats not the exact spelling, I'm using winXP now, and don't have raspppoe installed anymore.) Open that, and find the dword in there that has to to with MTU override. Change that number to what you want the MTU to be and reboot. That should do it.

Also don't go poking around in the protocol properties after changing it this way, or you could reset it and have to do that over again.

[crazyjw1971]

After reading EVILAJAX's and THE MYTH's post, I made the changes they recommended. This is the result...

_____________________________________________

TCP options string = 02040550010303020101080a000000000000000001010402

MTU = 1400
MTU is not fully optimized for broadband. Consider increasing your MTU to 1500 for better throughput.

MSS = 1360
Maximum useful data in each packet = 1348, which is less than MSS because of Timestamps, or other TCP/IP options used.
MSS is not fully optimized for broadband (although it might work well for slower connections). Consider increasing your MTU value.

Default Receive Window (RWIN) = 261628
RWIN Scaling (RFC1323) = 2 bits
Unscaled Receive Window = 65407
For optimum performance, consider changing RWIN to a multiple of MSS.
Other values for RWIN that might work well with your current MTU/MSS:
522240 (MSS x 48 * scale factor of 8)
261120 (MSS x 48 * scale factor of 4)
130560 (MSS x 48 * scale factor of 2)
65280 (MSS x 48)

bandwidth * delay product:
Your RcvWindow limits you to: 10465.12 kbps (1308.14 KBytes/s) @ 200ms
Your RcvWindow limits you to: 4186.048 kbps (523.256 KBytes/s) @ 500ms

MTU Discovery (RFC1191) = ON

Time to live left = 58 hops
TTL value is ok.

Timestamps (RFC1323) = ON
Note: Timestamps add 12 bytes to the TCP header of each packet, reducing the space available for useful data.

Selective Acknowledgements (RFC2018) = ON

IP type of service field (RFC1349)= 00000000


___________________________________


Now, this may have something to do with it...

A buddy of mine installed AOL 6.0 on my machine so that he could access some things in his email (couldnt get to it with aol.com). I think thats what messed everything up. Is there a way to undo the evil that was done do my PC? I'll hunt through the registry to see what I cant find.

I appreciate the help.

Any more suggestions?

[crazyjw1971]

I've tried and tried and I can't find out what the hell is wrong.

Can anybody help?

[EvilAjax]

I'm stumped :confused:

[crazyjw1971]

I formatted. I'll never let anyone install AOL 6.0 on my PC again!


Heres the new results...


TCP options string = 020405ac01010402

MTU = 1492
MTU seems to be optimized for PPPoE... If you are not on a PPPoE connection, consider increasing your MTU to 1500 for optimal throughput.

MSS = 1452
Maximum useful data in each packet = 1452, which is equal to MSS.
MSS is optimized for PPPoE. If you are not on a PPPoE connection, consider increasing your MTU value.

Default Receive Window (RWIN) = 17424
RWIN Scaling (RFC1323) = 0 bits
Unscaled Receive Window = 17424
RWIN is a multiple of MSS
Other values for RWIN that might work well with your current MTU/MSS:
511104 (MSS x 44 * scale factor of 8)
255552 (MSS x 44 * scale factor of 4)
127776 (MSS x 44 * scale factor of 2)
63888 (MSS x 44)

bandwidth * delay product:
Your RcvWindow limits you to: 696.96 kbps (87.12 KBytes/s) @ 200ms
Your RcvWindow limits you to: 278.784 kbps (34.848 KBytes/s) @ 500ms
Consider increasing your RWIN value to optimize TCP/IP for broadband.

MTU Discovery (RFC1191) = ON

Time to live left = 122 hops
TTL value is ok.

Timestamps (RFC1323) = OFF

Selective Acknowledgements (RFC2018) = ON

IP type of service field (RFC1349)= 00000000
_________________________________________



HAPPY, HAPPY, JOY, JOY!

:D :D :D:nod: :nod:

[crazyjw1971]

These are the DSLReports test results...



Your Tweakable Settings:
Receive Window (RWIN): 17424
Window Scaling: off
Path MTU Discovery: ON
RFC1323 Window Scaling: OFF
RFC1323 Time Stamping: OFF
Selective Acks: ON
MSS requested: 1452
TTL: 131
(less any hops behind firewall)
TTL remaining: 114


RWIN is in range
Looking good


Example 146000 byte download
Actual data bytes sent: 146000
Actual data packets: 101
Max packet sent (MTU): 1492
Max packet recd (MTU): 1492
Retransmitted data packets: 0
sacks you sent: 0
pushed data pkts: 15
data transmit time: 2.077 secs
our max idletime: 131.2 ms
transfer rate: 52680 bytes/sec
transfer rate: 421 kbits/sec
This is not a speed test!
transfer efficiency: 100%


Good data stream (no rexmits)


ICMP (ping) check
Minimum ping: 31 ms
Maximum ping: 56 ms
Ping stability:
32 32 32 35 34 56 34 32 31 32

Looking good


YEE HAW!!!

LOL, for now at least...

COME ON OCTOBER 31st!!!