Kitz Forum

Broadband Related => FTTC and FTTP Issues => Topic started by: hushcoden on February 04, 2018, 04:00:48 PM

Title: Optimal MTU value for Sky Fibre
Post by: hushcoden on February 04, 2018, 04:00:48 PM

I was having a read about the (best/optimal) value for the MTU (current set is 1500) and among other things I read that a way to find the 'optimal' size would be to perform a sustained ping test, i.e. I can use

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ping google.com -f -l <buffer size>If I try

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ping google.com -f -l 1500I get the message "Packet needs to be fragmented but DF set" and in order to not get that message I have to lower the buffer size to 1472.

So my question is: is this a problem and I should change the setting in my router from 1500 to 1472 or I can just ignore it...

Title: Re: Optimal MTU value for Sky Fibre
Post by: ejs on February 04, 2018, 04:09:57 PM

The value you give to the ping command does not include the size of the ICMP and IP headers.

1472 + 8 byte ICMP header + 20 byte IP header = 1500 MTU

Title: Re: Optimal MTU value for Sky Fibre
Post by: hushcoden on February 04, 2018, 04:38:00 PM

Thanks ejs, and does it mean I can leave the value at 1500 ?

Title: Re: Optimal MTU value for Sky Fibre
Post by: ejs on February 04, 2018, 04:56:29 PM

Short answer: Yes.

Longer answer: I suppose it may depend on exactly what you are trying to optimize. The ping command is more for finding the MTU between your computer and the destination, the MTU may not be the same for all destinations.