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Jason404
Aspiring Contributor
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Message 1 of 27

MTU setting for BT Infinity

What MTU setting should I set for my router.  The Tomato firmware that I am using has 1492 as the default.

 

Can anybody check to see what the default is on the BT Infinity hub please?

 

Cheers.

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Distinguished Guru
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Message 2 of 27

Re: MTU setting for BT Infinity

Have a look back a couple of threads on this site, there is one running on Infinity.

http://community.bt.com/t5/BB-in-Home/BT-INFINITY-HUB2/td-p/13699

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Jason404
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Message 3 of 27

Re: MTU setting for BT Infinity

Hey thanks, but I am already part of that discussion. 😄
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PheeragHfre
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Message 4 of 27

Re: MTU setting for BT Infinity

 


@Jason404 wrote:

What MTU setting should I set for my router.  The Tomato firmware that I am using has 1492 as the default.

 

Can anybody check to see what the default is on the BT Infinity hub please?

 

Cheers.


 

Ideally you shouldn't have packet fragmentation whilst entering or leaving your network.

 

Have you tried "pinging" the router(s) & then pinging a couple of external sources to check for this?

 

It should give you a good idea as to what the BT Infinity Hub MTU setting is or what it will accept.

 

Max MTU: How do I find mine?

 

 

"I have this awful feeling someone is watching every move I make (one of my pet hates is router location tagging)." Marvin (A paranoid Android)
Jason404
Aspiring Contributor
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Message 5 of 27

Re: MTU setting for BT Infinity

Thanks for that link - I'm learning something here.

 

I'm not sure whether I should change the Windows MTU setting to match the router's or not.  The default seems to be 1500.  Should I do the ping tests without touching the Windows default MTU setting? 

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PheeragHfre
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Message 6 of 27

Re: MTU setting for BT Infinity

 


@Jason404 wrote:

Thanks for that link - I'm learning something here.

 

I'm not sure whether I should change the Windows MTU setting to match the router's or not.  The default seems to be 1500.  Should I do the ping tests without touching the Windows default MTU setting?


 

You may find this utility useful, the latest version appears to be compatible with all current Windows versions.

SG TCP Optimizer

 

(as always check the download authenticity & use at you own risk.)

 

"I have this awful feeling someone is watching every move I make (one of my pet hates is router location tagging)." Marvin (A paranoid Android)
Guru
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Message 7 of 27

Re: MTU setting for BT Infinity

I would have thought BTs kit would support RFC4638 with baby jumbo frames to support 1500 byte MTU.

 

If not (which I doubt)  1492 should do it.

 

BT SIN 498 stipulates that the VDSL2 Active NTE supports all packet sizes ...

 

So I guess that a degree of "experimentation" should do no harm. (although effect will be minimal IMHO )

 

Although Windows default 1500 should work ok.

PheeragHfre
Recognised Expert
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Message 8 of 27

Re: MTU setting for BT Infinity

 


@RogerB wrote:

I would have thought BTs kit would support RFC4638 with baby jumbo frames to support 1500 byte MTU.

 

If not (which I doubt)  1492 should do it.


 

It is also worth mentioning.

 

If you decide to optimize the PC throughput for Internet use, this is likely to degrade throughput on your local Shares/drives or multimedia devices.

"I have this awful feeling someone is watching every move I make (one of my pet hates is router location tagging)." Marvin (A paranoid Android)
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IanC
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Message 9 of 27

Re: MTU setting for BT Infinity

 


@PheeragHfre wrote:

It is also worth mentioning.

 

If you decide to optimize the PC throughput for Internet use, this is likely to degrade throughput on your local Shares/drives or multimedia devices.


 

It's also worth mentioning that one needs to be careful, amongst all of this "tuning", of optimising your setup to work well with a particular site on The Internet - eg a particular speed test site.

 

Ordinarily I'd suggest leaving things at defaults unless there's a specific and compelling reason to change.

 

One such reason existed a few years ago, when it was advised to alter the MTU for BT broadband connections. This was nothing to do with packet fragmentation. Rather, BT's network at the time was assigning a low priority to packets of over a certain size (I don't recall the specifics) and reducing the MTU got around the problem while BT got around to implementing a fix. This situation hasn't existed for a long time though - in fact, it was fixed some time before I read about it...

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Guru
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Message 10 of 27

Re: MTU setting for BT Infinity

I think MTU tuning was fine ... in the early days of analog modems .... and differing ISP configurations, even now maybe on a long line with DMT, but I think it's fair to say the 21cn network will undoubtedly have been designed to cater for differing latency issues and data transmission across digital networks, whether they be UK based or otherwise.

I'd be very surprised if FTTC communications is not belts and braces (given that the vdsl2 modem accepts all packet sizes) and given the investment of the product and popularity of the 1500 byte packet size for transmission.

 

I frankly doubt whether you'd see any difference in changing it away from default .... given the speed and throughput of the product.

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