正解:B
When configuring VLAN trunking between a Cisco switch and a third-party switch, use IEEE 802.1Q. It is the open standard for VLAN tagging on Ethernet trunks. Cisco ISL was Cisco-proprietary and is obsolete on modern platforms. IEEE 802.1p relates to Class of Service marking inside the Ethernet header, not trunk encapsulation for interswitch VLAN transport. DSCP is an IP-layer QoS marking, not a Layer 2 VLAN trunking method. Cisco CCNA 200-301 v1.1 Network Access expects candidates to know that 802.1Q inserts a VLAN tag so multiple VLANs can traverse one physical trunk link. The native VLAN is carried untagged by default, while other VLANs are tagged. In multivendor networks, standards-based encapsulation is mandatory. Therefore, the action is to configure IEEE 802.1Q. The correct answer is B.