在配置PPP验证时有PAP和CHAP的选择，其中PAP为明文传送用户名和口令，不安全。而CHAP则采用哈希值进行验证，口令不会在网上传送，所以安全性比较高。

CHAP认证也是CCNA课程PPP教学时所需掌握的基本配置，其配置如下：

 

拓扑： RA DTE--------DCE RB
--------------------------------------
RA#conf t
RA(config)#username RB password hello
RA(config)#int s0
RA(config-if)#encap ppp
RA(config-if)#ppp au chap
RA(config-if)#end
-------------------------------
Router(config)#host RB
RB(config)#username RA password hello
RB(config)#int s0
RB(config-if)#encap ppp
RB(config-if)#ppp auth chap
%LINK-3-UPDOWN: Interface Serial0, changed state to up
%LINEPROTO-5-UPDOWN: Line protocol on Interface Serial0, changed state to up
------------------------------------------------------
RA#sh int s0
Serial0 is up, line protocol is up              -------第一层二层UP
  Hardware is HD64570
  Internet address is 1.1.1.1/30
  MTU 1500 bytes, BW 1544 Kbit, DLY 1000 usec, rely 255/255, load 1/255
  Encapsulation PPP, loopback not set, keepalive set (10 sec)
  LCP Open                                      -----------打开
  Open: IPCP, CDPCP                             -----------打开
  Last input 00:00:00, output 00:00:00, output hang never
  Last clearing of show interface counters never
  Queueing strategy: fifo