Cisco Certified Network Associate (CCNA) Practice Exam

Which trunking protocol adds a 32-bit field to Ethernet frames?

1. IEEE 802.1d

2. IEEE 802.3

3. IEEE 802.1q

4. IEEE 802.1p

The correct answer is: IEEE 802.1q

The correct choice is based on the functionality of the IEEE 802.1Q standard. This trunking protocol is specifically designed to enable VLAN (Virtual Local Area Network) tagging on Ethernet frames. By adding a 32-bit field known as the VLAN tag header, IEEE 802.1Q allows for the identification of VLAN membership for frames that traverse trunk links between switches. This tagging mechanism is essential for maintaining segregation of traffic from different VLANs on the same physical network infrastructure, ensuring that broadcast traffic is contained and not sent to devices that do not belong to the same VLAN. In contrast, the other options listed do not relate to the addition of a VLAN tag in the same way. IEEE 802.1d pertains to the spanning tree protocol which is used for preventing loops in network topologies. IEEE 802.3 refers to the standards for wired Ethernet itself and does not provide trunking capabilities. IEEE 802.1p deals with traffic prioritization in networks but does not involve VLAN tagging. Thus, among the options given, IEEE 802.1Q is the only protocol that specifically adds the necessary VLAN tagging field to facilitate trunking.