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

The command used to configure the VLAN number on a router subinterface is "encapsulation dot1q vlan-number." This command is essential for enabling IEEE 802.1Q encapsulation on the subinterface, allowing the router to distinguish traffic from different VLANs when it is routing between them.

When you create subinterfaces on a router for each VLAN, you must specify which VLAN each subinterface is associated with for proper functioning. The "dot1q" in the command denotes that the router is going to encapsulate the Ethernet frames in accordance with the 802.1Q standard, which is known for tagging VLAN information in Ethernet frames.

This encapsulation method allows the router to understand which VLAN a frame belongs to even if it is traversing a trunk link, enabling inter-VLAN routing. By providing the specific VLAN number in this command, you tell the router to handle incoming and outgoing traffic for that VLAN on the corresponding subinterface, effectively maintaining separation and proper routing between VLANs.