R1(config)#int s1/1
R1(config-if)#encapsulation ppp
R1(config-if)#ppp authentication pap
R1(config-if)#
*Mar 2 01:42:38.237: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1/1, changed state to down
R1(config-if)#exit
R1(config)#username R3 password cisco

R3(config)#int s1/1
R3(config-if)#do debug ppp authe
PPP authentication debugging is on
R3(config-if)#shut
R3(config-if)#
*Mar 2 02:40:26.045: %LINK-5-CHANGED: Interface Serial1/1, changed state to administratively down
*Mar 2 02:40:27.045: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1/1, changed state to down
R3(config-if)#no shut
R3(config-if)#
*Mar 2 02:40:31.001: %LINK-3-UPDOWN: Interface Serial1/1, changed state to up
R3(config-if)#
*Mar 2 02:40:31.009: Se1/1 PPP: Using default call direction
*Mar 2 02:40:31.013: Se1/1 PPP: Treating connection as a dedicated line
*Mar 2 02:40:31.013: Se1/1 PPP: Session handle[C000001C] Session id[29]
*Mar 2 02:40:31.017: Se1/1 PPP: Authorization required
*Mar 2 02:40:31.237: Se1/1 PPP: Authorization required
R3(config-if)#
*Mar 2 02:40:33.117: Se1/1 PPP: Authorization required
R3(config-if)#
*Mar 2 02:40:35.153: Se1/1 PPP: Authorization required
*Mar 2 02:40:37.153: Se1/1 PPP: Authorization required
*Mar 2 02:40:39.173: Se1/1 PPP: Authorization required
R3(config-if)#do un all
All possible debugging has been turned off

R3(config)#int s1/1
R3(config-if)#ppp pap sent-username R3 password cisco
R3(config-if)#
*Mar 2 02:40:54.165: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1/1, changed state to up