LCP (Link Control Protocol) is a part of the PPP (Point-to-Point Protocol) suite that provides essential services for the establishment, configuration, and maintenance of the link.
LCP is responsible for dynamic addressing, authentication (like PAP or CHAP), and multilink capabilities, which allow multiple physical connections to be bundled together.
Other protocols like NCP are used for configuring network layer protocols, but LCP handles these specific tasks.
Switches do not propagate VLAN information by default; you must configure the VTP domain. VLAN Trunking Protocol (VTP) is used to propagate VLAN information across a trunk link.