Ethernet Frame - Ethernet Frame Types

Ethernet Frame Types

There are several types of Ethernet frames. The different frame types have different formats and MTU values, but can coexist on the same physical medium.

• The Ethernet Version 2 or Ethernet II frame or DIX frame is the most common type in use today, as it is often used directly by the Internet Protocol.
• Novell's non-standard variation of raw IEEE 802.3 frame
• IEEE 802.2 Logical Link Control (LLC) frame
• Subnetwork Access Protocol (SNAP) frame

In addition, all four Ethernet frames types may optionally contain an IEEE 802.1Q tag to identify what VLAN it belongs to and its priority (quality of service). This encapsulation is defined in the IEEE 802.3ac specification and increases the maximum frame by 4 octets.

The IEEE 802.1Q tag, if present, is placed between the Source Address and the EtherType or Length fields. The first two octets of the tag are the Tag Protocol Identifier (TPID) value of 0x8100. This is located in the same place as the EtherType/Length field in untagged frames, so an EtherType value of 0x8100 means the frame is tagged, and the true EtherType/Length is located after the Q-tag. The TPID is followed by two octets containing the Tag Control Information (TCI) (the IEEE 802.1p priority (quality of service) and VLAN id). The Q-tag is followed by the rest of the frame, using one of the types described above.