Understanding ppp and LCP (1)

There are many topics to explain about the PPP protocol. This protocol is also widely used. Here we will focus on the content of LCP. First, let's take a look at the specific architecture of the ppp protocol.

I. Overview

1. It is a layer-2 protocol with the same status as HDLC and RARP.

2. PPP architecture:

(1) supports multiple upper-layer protocols, such as IP, IPX, and AppleTalk.

(2) It includes two Protocols: Network Control Protocol (NCP) and Link Control Protocol (LCP. LCP is used to negotiate with the underlying layer and then perform link layer authentication. Next, we will negotiate NCP, establish and configure network layer protocols such as IP addresses, and use them to negotiate with the third layer to encapsulate the upper layer data packets into the PPP. Both protocols are negotiated in two directions. Remove NCP before removing LCP.

3. LCP

The LCP Link Control Protocol (LCP) provides PPP with multi-functionality, considering the package format, package size, and authentication negotiation. It also enables PPP to determine when the line is failed and when it runs normally. LCP is used to configure and test data links. It works as follows:

Step 1: establish a link-first open the connection and then determine the relevant communication parameters (including MTU, compress type, and link authentication type. After the link is set, confirm the frame, and then the optional link quality validation phase. LCP determines the link quality.

Step 2 (required) authentication phase-Two authentication methods: Question Answer Handshake Authentication Protocol (CHAP) and password authentication protocol (PAP ). PPP itself does not require authentication. cisco router asynchronous lines require authentication. We recommend that you use CHAP authentication.

Step 2: Network Layer Protocol stage-LCP guides NCP to activate and configure network layer protocols. Data packets can be transmitted after the end of this phase.

Step 3: link termination-LCP guides NCP to disable layer 3.