Link Control Protocol (LCP)

Definition of Link Control Protocol (LCP) in Network Encyclopedia.

What is LCP (Link Control Protocol)?

LCP stands for Link Control Protocol, which is a subprotocol within the Point-to-Point Protocol (PPP) protocol suite that is responsible for link management.

How it works

LCP operates at the data-link layer (layer 2) of the Open Systems Interconnection (OSI) reference model for networking and is considered a data-link layer protocol. During establishment of a PPP communication session, LCP establishes the link, configures PPP options, and tests the quality of the line connection between the PPP client and PPP server. LCP automatically handles encapsulation format options and varies packet sizes over PPP communication links.

Link Control Protocol
Link Control Protocol

LCP also negotiates the type of authentication protocol used to establish the PPP session. Different authentication protocols are supported for satisfying the security needs of different environments. LCP can negotiate the following authentication protocols:

  • Password Authentication Protocol (PAP): Transmits passwords in clear text using a two-way handshake 
  • Shiva PAP (SPAP): A vendor-specific implementation of PAP 
  • Challenge Handshake Authentication Protocol (CHAP): Passes a password hash using a three-way handshake and is more secure than PAP or SPAP 
  • Microsoft Challenge Handshake Authentication Protocol (MS-CHAP): Microsoft’s implementation of CHAP, which is more secure than regular CHAP


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