MTU and MRU I understand correctly?

Question

Computer networks

Hello. There is a
Mikrotik and there is a connection to Provo via PPPoE (ADSL modem in bridge mode)
PPP connection gives the following parameters:
MTU-1480
MRU-1492
I understand correctly:
and by what formula is the second value calculated)?
2.MTU - how much can Mikrotik transfer to the dip?
3.MRU - how much maximum can Mikrotik take?

Answer 1

I think not quite right...
Both MTU and MRU CAN be changed - this is a configurable parameter! including and from the User side...
For Ethernet, the default maximum frame size is 1500 (together with all service headers and fields)... The "useful" packet length (containing data) is usually from 1475 to 1492
However, on low-quality communication channels ( this was especially true, for example, on DSL connections) when darned-darned telephone networks were used, it was necessary to reduce the MTU size to 1428 and below in order to avoid packet loss and retransmission ... For VPN, the MTU size sometimes had to be set to 1280!
In any case, when connecting, the size of the "reception / transmission window" is negotiated, and if MTU is set on your side, say 1450, then the other side will not send you packets with a length of 1500! Otherwise, on the other hand, the number of dropped packets will increase and the percentage of resent packets will increase ...
Something like this ...
You can read the details here

Answer 2

understand correctly.
most likely both are issued