Ethernet Header¶
Medium Access Control(MAC) Header¶
Destination MAC Address: This field specifies the MAC (Media Access Control) address of the intended recipient of the Ethernet frame. It is 6 bytes (48 bits) in length and is typically represented in hexadecimal notation. The destination MAC address identifies the network interface card (NIC) or device the frame addresses.
Source MAC Address: This field specifies the MAC address of the ethernet frame sender. Like the destination MAC address, it is 6 bytes (48 bits) in length and represented in hexadecimal notation. The source MAC address identifies the NIC or device that originated the frame.
Ether type: The EtherType field indicates the type of protocol data carried in the Ethernet frame's payload. It is 2 bytes (16 bits) in length. Alternatively, if the field contains a value less than or equal to 1500 (0x05DC in hexadecimal), it indicates the payload's size instead of the EtherType. This occurrence is known as the Length field.
| EtherType(hexadecimal) | Protocol |
|---|---|
| 0x0800 | Internet Protocol version 4 (IPv4) |
| 0x0806 | Address Resolution Protocol (ARP) |
| 0x0842 | Wake-on-LAN |
| 0x8035 | Reverse Address Resolution Protocol (RARP) |
| 0x8100 | VLAN-tagged frame |
| 0x86DD | Internet Protocol Version 6 (IPv6) |
| 0x8906 | Fibre Channel over Ethernet (FCoE) |
Data¶
Payload/Data: The payload field contains the data transmitted in the Ethernet frame. Depending on the EtherType or Length field, it can vary in size and carry various network layer protocols such as IPv4, IPv6, ARP, or other higher-layer protocols.
CRC¶
Cyclic Redundancy Check (CRC): A four-byte (32-bit) field that contains a cyclic redundancy check (CRC) value computed over the entire Ethernet frame (excluding the preamble and SFD). The receiving device uses the CRC value to detect errors in the frame caused by transmission errors or noise on the network.