What’s new in 6.20 (2014-Oct-01 10:06):
…
*) pppoe-server has auto mtu feature (enabled by default for new pppoe servers);
WHERE?! Could anyone answer - WHERE I can enable/disable or set THIS feature?
No one know? No one answer.
So - is that only “changelog feature”, not RouterOs feature? 
/interface pppoe-server server> set max-mtu=autoHTH,
Grzegorz, set it and check it at WinBox.
MTU has value “0” and is marked red colour as error!
Yes, you are right, but it’s probably Winbox error only.
/interface pppoe-server print detailshows proper MTU value.
Regards,
What will be difrence betwen 1480 and auto ? what will hapen when i set them auto ?
any help ?