ISL and DOT1Q are 2 encapsulation standards supporting Virtual LANs (VLANs) on an Ethernet network. These are the 2 frame tagging protocols that Cisco supports. The tagging protocol can be manually specified on a trunk port, or dynamically negotiated using Cisco’s proprietary Dynamic Trunking protocol (DTP).
A common query in LAN switching which we generally hear is the difference between ISL and DOT1Q encapsulation. Below table will showcase how both the terms differ from each other is terms of various parameters –