Ethernet Frame Structure

 Ethernet Frame Structure

• What's the purpose of the preamble?

It's out of 8 Zeros and indicates the start of a frame. So the receiving station knows, where the very first Bit of the Frame is.
After this, there comes the Frame Delimiter (SFD)

• How many bits are used for the MAC address?

Each MAC-address (Destination- Source-MAC-address) needs 6Bytes (48Bits).

• Where is the IPv4/IPv6 address hidden?

Inside the Destination & Source Address.

• How does the receiver distinguish between Ethernet and 802.3 frames? (difference between type/length field)

At the IEEE (Institute of Electrical and Electronics Engineers) 802.3, instead of a "Type"-Field, there is a "Length"-Field.

• Which algorithm is used for calculating the frame check sequence?

There is a checksum (32 Bit) inside. The Frame Check Sequence is going to be created at the transmitter. The recipient also calculates a checksum and compares it to the checksum of the transmitter.
If they don't match, the data block is going to be deleted.