PPP has built-in authentication in the form of Password Authentication Protocol (PAP) or Challenge Handshake Authentication Protocol (CHAP). PAP sends the passwords over the link in clear text, which poses a security risk, whereas CHAP sends a hashed value using MD5 security. Here is a CHAP configuration:
Figure 42.8 – PPP with CHAP
R1(config)#username R2 password Cisco
R1(config-if)#ip add . . .
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