MTU stuck on....

[stevelondon]

I noticed my speeds have slowed down a bit so i done the usual checks and noticed my MTU is 1460 i have always had it on 1500 as that is best for my connection i checked my router and registry and all says 1500 and last time i checked which was a couple of weeks ago it was 1500 now when i run the test its 1460 all of a sudden, i saw a post here about it somewhere and cant find it, i cant understand why its stuck on that when its always been 1500 anyone know a fix, its not really an issue as such but its weird how all of a sudden its lowered when my settings are all what its always been.  i have 2 pc's and its the same on both "scratches head"

[maxping]

I remember the thread , i think it said IDNet set it but I'm sure Simon said this is not true.

BTW in my routers stats -
Under WAN my MTU is 1500.
Under PPP  my MTU is  1492.

I don't know if this is how its supposed to be but it works fine for me.

[stevelondon]

Thanks for that i have always had mine set at 1500 it wont  go any higher than 1460 this is only happened in the last 2 weeks i use the SpeedTouch 585 v6 i tried my old Netgear DG834G yesterday and its exactly the same although everything is set to 1500 as Toyah sang with a lithp "Ith a mythtery" 

[Nerval]

Rikbean is the expert on MTU and RWIN, so no doubt he will post advice in due course Steve.

From experiments with rats that Rik and I did earlier, it seems that the MTU has a way of deciding for itself what it should be, and ignores some, but not all, attempts to change it.

I wonder if anybody really understands it.  Basso seems a bit more clued up on these things than many, but I don't know if it's beyond even him.  Whenever I've changed it, it's only ever made things worse, so now I leave it alone to go its own way - a bit like my cats.

[stevelondon]

It just seems strange how it has changed to the lower figure all of a sudden and will only go lower it wont increase to its original setting when ive always had it at 1500, RWIN is ok though.

[Rik]

Rikbean is the expert on MTU and RWIN, so no doubt he will post advice in due course Steve.

Finally got all the software back on the re-built desktop, so I can return to my proper job of patrolling forums. As for being an expert, I wouldn't say that, I've just experimented a lot...

From experiments with rats that Rik and I did earlier, it seems that the MTU has a way of deciding for itself what it should be, and ignores some, but not all, attempts to change it.

I wonder if anybody really understands it.  Basso seems a bit more clued up on these things than many, but I don't know if it's beyond even him.  Whenever I've changed it, it's only ever made things worse, so now I leave it alone to go its own way - a bit like my cats.

I came to IDNet from Nildram, using an MTU on router and computers of 1500. All the test sites I use faithfully reported back an MTU of 1460, suggesting that there's a 'throttle' somewhere in the IDNet setup. Simon thought, iirc, that it might be due to the way they have the system setup for users of VPN. Miriam recommends 1458, which is what I have changed to. However, I can ping the Beeb with a packet of 1472 bytes, which suggests that the 'throttle' is not universal. At which point I gave up and got on with using the service!

[MoHux]

I haven't tested this, but I think that if the RWin is a multiple of the MSS Windows will leave it alone.  If it's not, it will change it.
Whether it's consistent or not I don't know.

For interest, I have read that 'Vista' controls RWin and MTU dynamically, needing (allowing??) no input from the user.

[RostokMcSpoons]

Yup, I noticed this too.  DrTCP reports 1500, whilst www.netmonitor.org reports 1460.  Still, I've got the fastest connection I've ever had, so I'll leave it as is (for the moment - I can't help tweaking stuff)

[Rik]

I can't help tweaking stuff)

Welcome to the club!

[Rik]

For interest, I have read that 'Vista' controls RWin and MTU dynamically, needing (allowing??) no input from the user.

Oh good, more nannying... 

[Inactive]

- I can't help tweaking stuff)

I'm one of the " If it aint broke, don't fix it " brigade....

[Rik]

So am I normally, but as long as I keep records of my tweaks, I can't help myself when it comes to getting a few extra kbps...

[Thar]

I posted about the 1460 MTU thing some time ago link.

After upgrading the version of Zone Alarm I was using the MTU started to report correctly so I blamed ZA.

A couple of weeks ago I decided to do a Tweak Test on DSL Reports and the 1460 value was back!

I haven't changed my verison of ZA since so I don't know what has changed.

I was using a Netgear DG834G and am now using a Speedtouch 585.

Like the rest of you, I've given up worrying about it and decided to just get on with using the connection rather than fiddling with it. 

[stevelondon]

Hi i only checked it because my speeds reduced considerably i saw your post and done a clean uninstall of ZA on both pc's and nothing has changed my MTU is still 1460 my router and registry is on 1500 so im at a loss as to what it is all of a sudden unless IDNet has set it to that ive no idea but since its changed my speeds are a lot slower.

[Rik]

It's had no noticeable effect on my speed, but then I'm on a 2500 profile, so I miss the joys of wild speed changes. However, there definitely seems to be a 'choke point' within IDNet to 1460.

[wolverene]

After a disasterous 9 days on MAX getting speeds that continually fall from 100kbps immediately down to 0 - 3 kbps making it nigh on impossible to use the Net, and BT saying that speeds of 1kbps ( dial-up would feel like BB) are within the the accepted rules ( they obviously havent cottoned on that this is slow) I am going back to my 1Mb fixed . Hopefully BT havent buggared up my original line stats with all their fiddling. What a shame we cant talk to them direct, or maybe they dont want to admit to employing morons!!!

[wolverene]

After a disasterous 9 days on MAX getting speeds that continually fall from 100kbps immediately down to 0 - 3 kbps making it nigh on impossible to use the Net, and BT saying that speeds of 1kbps ( dial-up would feel like BB) are within the the accepted rules ( they obviously havent cottoned on that this is slow) I am going back to my 1Mb fixed . Hopefully BT havent buggared up my original line stats with all their fiddling. What a shame we cant talk to them direct, or maybe they dont want to admit to employing morons!!!
By the way I`m getting the 1460 reading as well

[wolverene]

Sorry about the doubl post, its been that kind of week

[Rik]

Been there... It would be worth sticking out your 10-day period with Max, after which CS can get their teeth into BT. For me, the cure was to get my target noise margin raised from 6db to 9db, which gave the line stability, and since then I've ticked along happily at ~2400kbps. I'd like to go faster, but on my line it isn't going to happen, and it's better than the 960kbps I had on a 1Mbps connection.

[wolverene]

Asked IDNet about raising  SNR to 9db and was told they tried this last week and it didnt make any difference. Funny thing is I never saw this happen on my router stats which I`ve been checking all the time so its back to 1Mb today.

[Rik]

When I had it done, it forced a lower sync speed, but gave the router enough 'headroom' to hang on to the signal at its noisiest. I was seeing it drop to -1 or -12db, which triggered a re-sync. By getting the extra 3db of headroom, I avoided the re-syncs but lost a small amount of speed, 400kbps.

IDNet CS will know better than me how effective this change in target noise margin is, but for me it definitely worked. I'd ask them to at least get it tried on your line before going back to vanilla ADSL, assuming the speed gains of Max are worth hanging on to (for me, they were).

[wolverene]

CS confirmed they put the interleaving on my line on 24 Nov but it didnt make any difference as far as they could see so they switched it back off. I must have blinked and missed it. Still they should be the ones to know and figure putting me back to std ADSL is what they are doing. Did you have a speed that just kept falling? Even when I managed a BT Test this showed a speed of 0 kbps and the next was 1kbps. The only speedtester I can use is the Giganews one as that is realtime and dont have any fancy graphics, that shows kicking in at anything up to 600kbps but drops straight away down to 45 and falls from there. It seems something called LCP keeps dropping then coming back up again. The ststs show that sometimes I have stayed syncd for up to 15 hrs without that happening but the speed is unusable. You might have better stats than my D/S Atten 63.5 and snr of 3 - 6.1db. Really suprised that CS didnt push that a speed on a BT Test showed 1kbps was not acceptable, BT must know this is wrong. got us by the "short & curlies" as the saying goes

[Rik]

You're right about BT.

I didn't have speed issues, no stuck BRAS profile or fluctuations, merely a line that dropped 10-12 times a day. For me, the target noise margin change fixed that, but it sounds like your problems are very different. FWIW, mt d/s attenuation is 56db, noise margin varies from 2-10db and sync from 2944 - 3424, the latter just bumping my BRAS profile from 2500 to 3000, but it doesn't last.

[wolverene]

I`ll swap ya-- go on  take up the challenge, it gives you something to do in life!

[Rik]

OK, what do I have to do???

[wolverene]

Well, we def need a long bit of 2 core wire and I`ll meet you half way up the M1
One good thing to come out of this is I`ll be able to save a fortune on haircuts. I`ve pulled all mine out!!!

[Rik]

OK, I'll pop down to Maplin and get a drum of Cat 5. As to the hair, grow a beard like me, it gives you more to go at!