What could be found instead of the EtherType field?

The EtherType field is a component of Ethernet frames that indicates the protocol being carried in the payload of the Ethernet frame, such as IPv4, IPv6, or ARP. When a virtual local area network (VLAN) is implemented, the Ethernet frame is modified to include a VLAN header instead of the traditional EtherType field.

This VLAN header, defined by the IEEE 802.1Q standard, carries information about the VLAN ID and priority information. By including this additional header, the Ethernet frame can indicate which VLAN the frame belongs to, allowing for better segmentation and management of network traffic. The presence of a VLAN header is particularly important in environments where multiple VLANs are used, as it helps to effectively isolate and route traffic.

In contrast, a TCP header or an IP header can be found within the payload of the Ethernet frame, following the EtherType or VLAN header, depending on the frame's structure. The checksum field is typically used for error-checking in protocols but does not replace the EtherType field.