Subinterfaces are logical divisions of a physical interface that allow a router to communicate with multiple networks using a single LAN port. Subinterfaces can have different IP addresses, VLANs, and routing protocols. They are useful for reducing the number of physical interfaces and cables needed, as well as improving network performance and security. Reference: Subinterfaces - CompTIA Network+ N10-008 Domain 1.21 - YouTube1 CompTIA Network+ Certification Exam Objectives, page 92