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optimum MTU value using 3rd party router ?

karlos103
Grafter
Posts: 106
Registered: 26-01-2014

optimum MTU value using 3rd party router ?

Hi all
Im using a Netgear R7000 router with my openreach fibre modem and wanted to know if there is an optimum setting for MTU ?
Default is 1492 .
Have read if using 3rd party router with openreach modem then should be set to 1458 (BT advised someone)
Also heard 1400 is best setting .
Any help most appreciated
Karl
6 REPLIES
Plusnet Help Team
Plusnet Help Team
Posts: 12,982
Thanks: 141
Fixes: 46
Registered: 27-04-2007

Re: optimum MTU value using 3rd party router ?

Hi there,
I've also heard of people using the MTU at 1458 when using a third party router with FTTC, I'd try that, if not see what 1400 does.
If this post resolved your issue please click the 'This fixed my problem' button
 Adam Walker
 Plusnet Help Team
Community Veteran
Posts: 1,990
Thanks: 5
Registered: 11-12-2013

Re: optimum MTU value using 3rd party router ?

I dont know how 1400 has ever been determined to be a optimal value, it seems one of those internet myths that just wont stop spreading.
Without RFC 4638 the optimal value is 1492, with RFC 4638 its 1500.
karlos103
Grafter
Posts: 106
Registered: 26-01-2014

Re: optimum MTU value using 3rd party router ?

Thanks for the replies.
What is RFC ?
Probably give the 1458 setting a go… see if makes any difference… can soon change back lol
Karl
RealAleMadrid
Seasoned Pro
Posts: 653
Thanks: 239
Fixes: 10
Registered: 07-07-2009

Re: optimum MTU value using 3rd party router ?

The standard MTU for a PPPOE connection as used on BT Wholesale fibre is 1492. So why not use that! Smiley
Ethernet Frame length is 1500 bytes with an 8 byte overhead for PPPOE. I believe RFC4638 which probably isn't supported by your router allows an increased frame length.
As for 1458, wasn't that some strange anomaly on AOL dial up, certainly not relevant now. 1400 - I don't think so!
karlos103
Grafter
Posts: 106
Registered: 26-01-2014

Re: optimum MTU value using 3rd party router ?

Ok , will try 1458 out of interest… if no different then will stick with 1492… default setting .
Cheers
NorthPole
Aspiring Pro
Posts: 255
Thanks: 39
Fixes: 6
Registered: 05-07-2013

Re: optimum MTU value using 3rd party router ?

I'm sure I've seen previous posts from Plusnet staff in response to a similar question recommending an MTU of 1500.