What command is used to configure the native VLAN on a router subinterface?

The command used to configure the native VLAN on a router subinterface is indeed "encapsulation dot1q vlan-id native." This command is crucial in networks where 802.1Q trunking is employed, as it designates a specific VLAN as the native VLAN on that trunk link.

In 802.1Q trunking, the native VLAN is the VLAN that does not have an 802.1Q tag applied to its frames as they traverse the trunk link. By setting the native VLAN on a router subinterface, you ensure that untagged frames are correctly handled according to the designated VLAN, which helps prevent issues like VLAN hopping and ensures proper segmentation of network traffic.

The command structure clearly specifies the encapsulation type (dot1q) and associates a particular VLAN ID with the 'native' keyword, making it straightforward to configure and understand. This is essential for maintaining network integrity and performance in VLAN implementations.