cancel
Showing results for 
Search instead for 
Did you mean: 

MTU Question??

N/A

MTU Question??

When you try this tweak thing in DR TCP to get the max out of your connection, do you have to set the MTU just in the DR TCP software or in the router to the same values aswell?.


Thanks
13 REPLIES
zpeterk
Grafter
Posts: 377
Registered: 14-04-2007

MTU Question??

You need the same value on both
N/A

MTU Question??

Thanks for that but i think i have noticed a difference just changing the values on the DR TCP software, can anyone second this that you have to put the values in both router and software to notice any difference.?


Thanks
N/A

MTU Question??

As stated, the same MTU needs to be used for the NIC and the router. Otherwise, the router has to cut and control the extra transmission unit size from the NIC, taking up time and hence speed.
michaelscott
Grafter
Posts: 594
Registered: 09-08-2007

MTU Question??

Having a value on the NIC that is higher than the MTU on the router can often cause problems, so as already stated: change it on both and any other machines connected to the router aswell Smiley
N/A

MTU Question??

Confused in the router there are more options,

MRU 1492
MTU 1492
MSS 1432


Going back to the posts above iv'e changed my MTU in DR TCP to 1430, so do i just change this or all those above MRU, MTU, and MSS??


Thanks. Smiley
Community Veteran
Posts: 14,469
Registered: 30-07-2007

MTU Question??

It depends on whether the NIC/router automatically adjusts the MRU and MSS values when you change the MTU.

If it does not, then MSS (Maximum Segment Size) should to 40 less than MTU (Maximum Transmition Unit) and MRU (Maximum Receive Unit) should be the same as MTU.
N/A

MTU Question??

Quote
iv'e changed my MTU in DR TCP to 1430


1430 seems a little low to me. Try about 1475.
N/A

MTU Question??

So in the router put...

MTU 1430
MRU 1430
MSS 1390


Is that the correct setting to put in my router then? iv'e choice 1430 for MTU as i think it works best for me. Just confrm thats right above, also after i have changed these in the router i have to go around all my other pcs and just change the MTU on them to 1430, correct.?


Thanks
N/A

MTU Question??

Simply, YES.

Although I still think 1430 is a bit low. I use 1478.
N/A

MTU Question??

Why do you think that? when you have used 1430 what problems have you had??



Thanks.
Community Veteran
Posts: 14,469
Registered: 30-07-2007

MTU Question??

In theory, the higher the MTU figure the better the throughput you can get because it will be able to get more data in each IP packet and thus require less packets, and hence less packet header overhead.

The common MTU values often quoted are 1458, 1478 and 1492 but generally MTUs below those figures don't produce your best throughputs.

However, maximum throughput will vary from connection to connection and one MTU value may work for one but not work for another, This is why we recommend you try several different MTU values to see which one works best for your connection. Also remember the RWIN value in Windows must be adjusted in line wih the MTU (i.e. it ideally must be a multiple of the MTU value), but again what multiple to use can only be determined by trial and error (i.e. try and test).

The tweak test on dslreports can often give you a good indication of the best setting to use but as always they may not always produce the best throughput.
N/A

MTU Question??

For every installation, there will be an optimal MTU. If you do not have the optimal figure, then all that will happen is that you do not get maximum speed.

It's a bit like opening a hot water tap in relation to your hot water pressure / heating capacity. Too little and you will not fill the bath quick enough. Too much and you may drain the system before it gets a chance to heat up.

If you look at the "MTU tweaking thread" you may get some ideas.
http://portal.plus.net/central/forums/viewtopic.php?t=12116
I am not saying 1430 is wrong, just seems low since BT upgraded the system to handle MTU's at 1500 better
painswck
Grafter
Posts: 449
Registered: 30-07-2007

MTU Question??

In common with a lot of people on ADSLguide I find a value of 1430 gives best speeds on 512 with PlusNet, even after the BT updates.

Goes against some of the theory but works.

Just my 2p worth.

Roland