MTU and FTTC

_Paul

_Paul

_Paul

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PDR Croydon
I've got Infinity and changed from an old WRT54GL/DD-WRT to an RV220W. While going through the PPPoE settings I noticed an MTU value. I know traditionally PPPoE connection had to be 1492 or less but my understanding is that the Huawei modem and infinity will support up to 1500. Out of curiosity I ran the checker on speedguide.net and that is reporting back an MTU of 1420. I've set the MTU setting in the router to auto and also manually to 1492 (for some reason the firmware won't let me set it to 1500, presumably some legacy support issue) but still get the same result. Windows 7 MTU is defaulted to 1500.

My question is, does having a lower MTU lead to any problems?
 
It shouldn't. TCP/IP is isn't normally sent in blocks that large, and they are fragmented to smaller amounts anyway.
 
David91 said:
It shouldn't. TCP/IP is isn't normally sent in blocks that large, and they are fragmented to smaller amounts anyway.
Click to expand...

This. Also doesn't matter what Windows is set to, it will negotiate with the router when sending packets and lower its value accordingly.
 
Thanks.

I guess the part that was throwing me was the router being set to 1492 but the test showing 1420. When I connected the Openreach modem directly to my PC I was getting 1480.

Looking in to it a bit further, when I ping a webserver I can use up to 1456 bytes before I get the fragmented error. 1456+28+8=1492 but I thought the 8 bytes for the PPPoE header wasn't included in the MTU size?

I'm happy enough with the connection speed so this isn't an attempt to eek the last drop of performance out of it but I would have thought if everything was correctly configured the overhead for the router and NIC would be lower.
 
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