An Authenticate-Request packet is sent by the calling party to the called party. The Data field
has four fields:
Peer-ID length Eight bits long; indicates the length of the Peer-ID.
Peer-ID Zero or more octets long; contains the username.
Passwd-length Eight bits long; indicates the length of the password.
Password Zero or more octets long; contains the cleartext password.
The called end will respond with either an Authenticate-Ack (Type 2) or Authenticate-Nak
(Type 3) packet. Both packets have two fields as data. One is Msg-Length (8 bits), and the other
is Message (one or more octets).
The following output is from a debug ppp authentication command on a router that is
authenticating by using PAP with PPP:
BR0/0:1 PPP: Phase is AUTHENTICATING, by the peer
BR0/0:1 PAP: O AUTH-REQ id 3 len 14 from "r3"
BR0/0:1 PAP: I AUTH-ACK id 3 len 5
You can follow this debug PPP authentication router output by referring to Figure 26.7.