I need some clarifcation regarding the MTU concept.
I know that IP MTU is 1500 bytes and that includes IP header+TCP header+payload
What about ethernet MTU?
- Is it equal to IP MTU that is to say 1500 bytes?
- Or it is 1514 bytes --> IP MTU +14 bytes Ehternet header(6-SA+6-DA+2-Ethertype) whithout preamble and CRC?
- When configuring system MTU are we talking about Ethernet MTU without header?
- What about ethernet MTU on a trunk?
I am a bit confused when trying to understand QinQ for example. Why should the system MTU be 1504? I know that we are adding a tag of 4 bytes but the tag is in the header right. If you are taking in consideration that ethernet MTU is the IP MTU that is to say 1500 so the 4 bytes of the tag are not taking into account as ethernet MTU would without header.
Would be nice to get some clarification there.