I am a bit confused about the understanding of the relationship between minimum MTU of MTU and minimum Ethernet frame size.
We know that the maximum MTU of Ethernet is 1500 Bytes which makes the maximum frame size equal to 1518 Bytes (1500+18) or 1522 Bytes (1500+22).
We also know that the minimum MTU is 576 Bytes.
So confusing part and my question is, why isn't the minimum frame size 594 Bytes(576+18) or 598 Bytes (576+22)? And instead, the minimum frame size is 64 Bytes.
I feel I'm missing something here and that's why I don't understand the relation between these two.
Best Answer
You are confusing a few things.
The MTU - maximum transmission unit - is the largest IP packet an underlying protocol or a link can carry - the maximum IP PDU size.
For Ethernet, the largest standard frame is 1518 bytes. 18 bytes are frame overhead, so the largest payload (L2 SDU) is 1500 bytes, so that's the MTU (maximum L3 PDU) over Ethernet as well.
Ethernet's minimum frame size is 64 bytes, but that has no relation to the MTU. (IP packets smaller than 64-18=46 bytes simply require padding.)
576 bytes is the smallest unfragmented IPv4 packet size that an underlying protocol or link needs to support. Since Ethernet's maximum payload size is larger than 576 bytes, that is of now consequence here.