How are frames calculated?

Question

Computer networks

I'm confused about frames (frames). How is it calculated I do not understand? MTU should be constant or not? - in my router and on the network card, different default values ​​\u200b\u200bare set, and in the network card this value is larger.
And what is included in the MTU - only the payload or the entire frame? The information on this subject is contradictory, somewhere they write that this is the MTU - this is the entire frame, somewhere, that is only the payload. How is it really, someone brazenly lies in any way? It is unlikely that the receiving device, having an MTU limit of, for example, 1500, thinks: "so, what would I calculate - the entire frame 1540 or the payload 1500 ..... accept or not accept, how to be ..... error...error ...... "
And it is not clear how the receiving device understands where the frame ends, because according to Wikipediahttps://en.wikipedia.org/wiki/Ethernet payload can be variable and total frame length or payload length not specified?

Answer 1

https://habrahabr.ru/post/226807/