The Point-to-Point Protocol provides a standard method for transporting multi-protocol datagrams over point-to-point links.
PPP was originally designed as an encapsulation protocol for transmitting IP traffic between two peer nodes.
In the TCP/IP protocol suite, it is a data link layer protocol (Layer 2 in the OSI model) used for synchronous modem connections, replacing the original non-standard Layer 2 protocol, SLIP.
I. PPP, or Point-to-Point Protocol, is a data link layer protocol for point-to-point type lines introduced by the IETF. It is not a proprietary protocol, allowing interconnection of devices from different vendors. It supports multiple protocols, provides optional identity authentication services, can compress data in various ways, supports dynamic address negotiation, and supports multi-link bundling.
II. Password Authentication Protocol (PAP). PAP is a two-way handshake authentication protocol. When the link is first initialized, the peer being authenticated initiates the authentication request by sending a username and password to the authenticator for identity verification. The password is sent in plaintext, so security is relatively low. PAP supports one-way and two-way authentication, with authentication flowcharts covering both.
II. Challenge Handshake Authentication Protocol (CHAP). CHAP verifies the identity of the peer being authenticated through a three-way handshake, completed during the initial link establishment. To enhance security, verification is performed periodically after the link is established. CHAP is more secure than PAP because it does not send plaintext over the line; instead, it sends a random number sequence hashed with MD5. CHAP supports one-way and two-way authentication.
III. Configuration Process:
hostname R_A
interface Serial2/0
address 192.168.1.1 255.255.255.0
encapsulation ppp
ppp pap sent-username R_A password 0 123
clock rate 64000
R_A(config-if)#ip address 192.168.1.1 255.255.255.0
R_A(config-if)#no shutdown
%LINK-5-CHANGED: Interface Serial2/0锛?changed state to up
Router>en
Router#conf t
Enter configuration commands锛?one per line. End with CNTL/Z.
Router(config)#hostname R_B
R_B(config)#username R_A password 0 123
R_B(config)#interface s3/0
R_B(config-if)#encapsulation ppp
R_B(config-if)#ppp authentication pap
R_B(config-if)#ip address 192.168.1.2 255.255.255.0
R_B(config-if)#no shutdown
Finally, pay attention to the correspondence between usernames, passwords, and routers; the information correspondence between the authenticator and the authenticated peer; authentication information is case-sensitive; if the configuration does not take effect after modification, try restarting the port. PPP uses 7EH as the start and end flag (F) of a frame;
Where the Address field (A) and Control field (C) use fixed values (A=FFH, C=03H); the Protocol field (two bytes) uses 0021H for IP packets,