How do I adjust MTU size?

[snowboy]

Hi,

I've read the tweak help on adjusting MTU size (I'm trying to lower to see if it helps with a online game problem), and have put an entry in the relevant sections of the reg (System, services, tcpip, parameters, intereface, interface) . DWORD entry Value 576 and turned off enablePMTUdicovery. Running Win2k, with DSL connection.

I have two interfaces mentioned, done it on each. Yet whenever I run the tweak program it still registers as being 1400.

My output from the tweak is :

TCP options string = 020405500103030201010402

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 = 1360, which is equal to MSS.
MSS is not fully optimized for broadband (although it might work well for slower connections). Consider increasing your MTU value.

Default Receive Window (RWIN) = 256960
RWIN Scaling (RFC1323) = 2 bits
Unscaled Receive Window = 64240
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: 10278.4 kbps (1284.8 KBytes/s) @ 200ms
Your RcvWindow limits you to: 4111.36 kbps (513.92 KBytes/s) @ 500ms

MTU Discovery (RFC1191) = OFF

Time to live left = 47 hops
TTL value is ok.

Timestamps (RFC1323) = OFF

Selective Acknowledgements (RFC2018) = ON

IP type of service field (RFC1349)= 00000000



Please help,

Snow

[xbit]

You don't have a patch installed. Click on the link below to download The win2k ppoe patch.

http://www.speedguide.net/files/sguide_tweak_2k_pppoe.zip

[snowboy]

Hi,

Installed it ok. MTU size still reports the same size and still getting the same problem, tweak report is :

TCP options string = 020405500103030201010402

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 = 1360, which is equal to MSS.
MSS is not fully optimized for broadband (although it might work well for slower connections). Consider increasing your MTU value.

Default Receive Window (RWIN) = 255552
RWIN Scaling (RFC1323) = 2 bits
Unscaled Receive Window = 63888
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: 10222.08 kbps (1277.76 KBytes/s) @ 200ms
Your RcvWindow limits you to: 4088.832 kbps (511.104 KBytes/s) @ 500ms

MTU Discovery (RFC1191) = ON

Time to live left = 47 hops
TTL value is ok.

Timestamps (RFC1323) = OFF

Selective Acknowledgements (RFC2018) = ON

IP type of service field (RFC1349)= 00000000

Thanks,

Snow

[Lobo]

First are you on PPPoE or regular DSL


PPPoE you have to log on with name and password.
PPPoE ( Point-to-Point Protocol over Ethernet ) is a method for building PPP sessions and encapsulating packets, as described in RFC2516. Although it is not a standard, PPPoE is already being used by a number of DSL providers. It requires either routers that have built-in PPPoE support, or PPPoE software to "dial up" and establish the session.

[HalfLifer]

Looks like PPPoE is limiting this...quite odd since it should max at 1492, not 1400.

[Lobo]

I know how to change MTU but first we need to know if it should be 1492 or 1500, PPPoE, do you have to log on to net everytime with name and password, if nothing else call provider and ask them

[snowboy]

OK,

Not sure if it is PPPoE although I do log on with user name password. My router is an alcatlel speed touch home, is there any way of verifying if ti is PPPoE.

Also trying tom optimise for online gaming and from what I read small packets sem better for responsiveness - don't really have noticable throughput problems.

Wondering as well if it is a Win2K related issue, is there something there I can change?

Cheers,

Snow

[Lobo]

First changing MTU to 576 (Dialup MTU) will not help in gaming, go to online gaming foum for help
2. Call your provider to see if you are on PPPoE, very important as the MTU is different than regular DSL
OK in example it says MTU 1454, just look for yours 1400 and change, PPPoE is 1492, Regular dsl is 1500
and if your on regular DSL we have some numbers to change as you installed PPPoE patch, do this:

Go to help page below in signature, middle of 1st page click on DSL, pay attention to MaxFrameSize, after you change, REBOOT or it will not work. Remember this is the only way and you must reboot first, then take analyzer test

[snowboy]

Can't check with the ISP just now (Out of hours),

Adjusted to 1492 although can't find a reg entry for maxframesize.

Tweak still reports MTU as being 1400 (reboted with new settings),

Didn't realise there was a game forum - whouls I continure this post there or keep going with this?

Thanks,

Snow

[Lobo]

Also make sure you have lastest firmware for your router, will affect MTU

[HalfLifer]

MTU affects TCP/IP, and games use UDP, so MTU wont affect it.