Kitz Forum
Internet => General Internet => Topic started by: JGO on March 29, 2014, 08:27:15 AM
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Kitz advice on MTU and RWIN is comprehensive but written for older OS and systems. (People will bring out new models !)
Please can someone clarify/update :=
1) Does the advice that later O/S look after RWIN themselves apply to ALL later O/S ?
2) Provided the modem MTU is set equal or higher than the computer's it is not essential that both are the same. BUT how much difference does it make making them the same ?
I appreciate that this depends on the other end MTU so any gain is statistical.
Common sense says none, but I've seen expensive mistakes due to common sense ! I'm thinking of someone who always took the hot ashes out in a bucket, so when someone bought him a plastic bucket ---- YES HE DID !
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The modem/router MTU should be either the same as the computer, or it should be 1500. What you shouldn't do is something like this:
Computer MTU: 1460
Modem/router MTU: 1480
because that can result in two levels of fragmentation in some circumstances. Assuming that MRU is the same as MTU, which it normally is, incoming packets greater than 1480 bytes would be fragmented into 1480 byte chunks by the modem/router, and then these would be fragmented again into 1460 byte chunks by the PC.
The best option in my opinion is to set the modem/router MTU to 1500, because it's then effectively 'transparent' as far as fragmentation is concerned. But this does mean that all connected devices may need to be individually set to appropriate MTU values.
I don't know about Windows, but what I find with Linux is that setting everything to an MTU of 1500 works fine - the actual MTUs get adjusted automatically as needed.
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Many thanks, that is what I thought. Changing from both 1500 to Win 1458, Modem 1500, may have helped with some websites but not spectacular, so probably nothing significant to be gained by other changes for me.
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1) Does the advice that later O/S look after RWIN themselves apply to ALL later O/S ?
With Windows Vista onwards - yes... although you can still run into the occasional RWIN issue.
I have very recently discovered to my cost that nvStreamsvc which is installed by nvidia has some sort of issues with RWIN and can upset your network. The post explaining it is somewhere on their forums, but iirc it has difficultly in being able to calculate the MSS or windows scaling correctly, and can slow things down (http://forum.kitz.co.uk/index.php?topic=13735.msg258720#msg258720) quite considerably. :(
Provided the modem MTU is set equal or higher than the computer's it is not essential that both are the same. BUT how much difference does it make making them the same ?
Erics already explained most of it. I agree leave it at 1500 on the router, then traffic will go through without any need for further fragmentation that wont have already occured elsewhere. MTU is end to end point and all computers/devices should have a default setting even if it doesnt dynamically adjust anyhow. As long as the router isnt set to less you should be fine.
Now that broadband has been out a lot longer, most operating systems handle MTU & RWIN better. Most of the earlier issues have been ironed out and we dont see as many problems as we did 10 yrs ago.
iirc theres only the xbox where you may have to adjust settings on your router. *
Plus - 10yrs ago tweaking your MTU and ekeing out an extra 50kbps was a fantastic result. In the days of 256kb even an extra 20kbps was thought worth tweaking for. These days you wouldnt really notice any difference in a 20-50 kbps tweak.
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Thank you too kitz.
I think I've made a minor difference on one or two sites but not sure, my wife hasn't noticed anything in her browsing ! Guess it is still a bit like interference, the best method is what works !
Thanks again both.
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Agreeing with all of the above and just mentioning the configuration of devices in The Cattery . . .
None of the Huawei EchoLife Home Gateways that I use (HG610, HG612 or HG622) have the means to adjust the MTU. Every system connected to the LAN (all Linux kernel based OS devices) has its Ethernet port configured with MTU: auto.