Refer to the exhibit A new VLAN and switch are added to the network. A remote engineer configures OldSwitch and must ensure that the configuration meets these requirements: - accommodates current conf

The `switchport mode dynamic` command uses DTP to negotiate trunking, but it does not guarantee 802.1Q encapsulation or prevent the negotiation of ISL if both sides support it.

The `no switchport mode trunk` command would disable trunking altogether, preventing the accommodation of multiple VLANs, including VLAN 20.

The `switchport nonegotiate` command disables DTP, but it doesn't explicitly enforce 802.1Q encapsulation; it requires `switchport trunk encapsulation dot1q` to be manually set in conjunction if ISL is a possibility.

The command `no switchport trunk encapsulation isl` explicitly disables Cisco's proprietary ISL trunking encapsulation, forcing the interface to use the IEEE 802.1Q standard for VLAN tagging, which meets the requirement for IEEE standard support.