one way chap authentication

[trevelle@xxxxxxxxxx]

I am working on internetworkExpert lap 4 HDLC/PPP portion. The task at hand is for R5 to request that R4 authenticate VIA PPP with a MD5 hash value that represent the password CISCO. I got it to work using the current config, but the configuration guide does not use ppp chap password 0 CISCO command on R4. When I take the command out the ser 0/1 interfaceS goes down. Am I missing something? 






R5
username Rack1R4 password 0 CISCO

interface Serial0/1
 ip address 141.1.45.5 255.255.255.0
 encapsulation ppp
 ppp authentication chap


R4
username Rack1R5 password 0 CISCO

interface Serial0/1
 ip address 141.1.45.4 255.255.255.0
 encapsulation ppp
 ppp chap password 0 CISCO
end