Point-to-Point Protocol
SLIP
PPP (point-to-point protocol).
PPP (Point-to-Point Protocol)
PPP
Network Control Protocol is uses to identify the Network layer protocol used in the packet
HDLC
Point-to-Point Protocol (PPP) is the most commonly used protocol for dial-up connections.
PPP is point to point protocol. It does single channel network links, usually over a long distance, or a VPN. The program that sets up and manages PPP connections is pppd.
Network control protocol
there may be the issue with the layer 2 protocol like hdlc or ppp is not configured or wrongly configured if the interface is serial interface.
The full form of PPP is Point-to-Point Protocol. It is a data link protocol used to establish a direct connection between two nodes in a network. PPP is commonly used in connecting computers to the internet via dial-up or dedicated connections.
LCP sets up the PPP connection and its parameters. NCP handles higher layer protocol configurations.