Hello,
I have this topology
PPPoE MIkrotik Server (NAS) -----> Wireless Link ------> RB750 -----> Bridge —> RB411 (Access Point) Wireless NV2 —> CPEs
So the bridge on RB750 Bridge togheter the RB750 ether1 and RB411 ether1 (bridged with wlan1)
Can someone explain me how I should set the NAS, RB750 and RB411 ethernets MTU and L2MTU.
The will be to bring the PPPoE sessions that begin into the CPE from the Access Point to the NAS using MPLS+VPLS
How i should configure the PPPoE MRU ?
can you help me? 
please ask if more detail are needed.
My goal is to understand how many bytes are required for VPLS and ethernet interfaces to transport PPPoE without fragmentation.
I tought 1522 L2MTU and 1500MTU, but it seems breaks the PPPoE.
Thanks!
Please read article about required L2MTUs.
http://wiki.mikrotik.com/wiki/Manual:Maximum_Transmission_Unit_on_RouterBoards#VPLS_Tunnel
1526 should be supported to forward 1500byte ethernet frame over VPLS, PPPoE header is 8 bytes.