ckgth
1
Hello!
can you confirm this?
Since I have I upgraded my RB/433AH from 3.16 to 3.18 not only the eth1-Port makes MTU=1600.
With 3.16 i can make only make on eth1 1600, but with the 3.18 i can’t make this not yet on eth1! 
kind regards
Christian
uldis
2
RB433AH doesn’t support such high MTU, and that is why it doesn’t allow to select it.
Please see this page to know what is the MTU for each RB:
http://wiki.mikrotik.com/wiki/Maximum_Transmission_Unit_on_RouterBoards