EtherType

EtherType is a two-byte field in Ethernet frames that identifies the protocol carried by the payload. It enables multiplexing multiple network-layer protocols over a single Ethernet link by signaling how to interpret the data that follows.

In Ethernet II framing, the EtherType field appears after the source MAC address. The value indicates what protocol occupies the frame’s payload, such as IPv4, IPv6, or ARP. This approach distinguishes the payload without using a length field. By contrast, older IEEE 802.3 frames originally used a length field and relied on LLC/SNAP headers to indicate the higher-layer protocol.

Common EtherType values include 0x0800 for IPv4, 0x0806 for ARP, and 0x86DD for IPv6. Other values identify different protocols or services, such as 0x8847 for MPLS unicast and 0x8848 for MPLS multicast. In frames that use VLAN tagging (IEEE 802.1Q), a 4-byte tag is inserted after the destination and source MAC addresses. The first two bytes of the tag are 0x8100, indicating a VLAN tag; the original EtherType value for the payload appears after the tag.

Assignment and governance of EtherType values are managed by the IEEE Registration Authority, ensuring global uniqueness. Devices such as switches and network interface cards rely on EtherType to dispatch received frames to the appropriate upper-layer protocol handler.

Overview of usage remains essential for network design and troubleshooting, as EtherType defines how a frame’s payload should be processed and routed within the host or network stack.