Cisco Certified Network Professional 2026 – 400 Free Practice Questions to Pass the Exam

The default encapsulation method for trunk links in Cisco switches is 802.1Q. This standard, developed by the IEEE, enables VLAN tagging on Ethernet frames, allowing multiple VLANs to coexist on a single physical link.

When a trunk link is established, it is essential for the switch to recognize which frames belong to which VLAN. The 802.1Q method accomplishes this by adding a tag to the Ethernet frame that signifies the VLAN to which the frame belongs. This tagging allows for the appropriate forwarding of frames based on VLAN identifiers at each switch along the trunk path, ensuring network segmentation and preventing broadcast storms across VLANs.

ISL (inter-Switch Link) was a proprietary encapsulation method developed by Cisco but is no longer the default for newer switches. While it may still be supported for backward compatibility, the industry standard 802.1Q has become the prevalent method due to its open nature and widespread adoption. Therefore, modern Cisco switches default to using 802.1Q for trunk link encapsulation, making it the correct choice in this context.