User`s guide

XSR Users Guide 105
Chapter 6 PPP Features
Configuring PPP
Network Control Protocol (NCP)
The Network Control Protocol (NCP) handles transmission and reception of
various network layer control packets and datagrams. NCP provides:
Sets up network layer control protocols over the established PPP link.
Transmits/receives network layer datagrams if the corresponding
NCP is successfully negotiated.
The configuration negotiation procedures are performed once the LCP
reaches the OPENED state.
Authentication
Authentication protocols, as referenced in RFC-1334, are used primarily by
hosts and routers to connect to a PPP network server via switched circuits or
dialup lines, but might be applied to dedicated links as well. The server can
use identification of the connecting host or router to select options for
network layer negotiations.
The authentication protocol used is negotiated with the peer entity via LCP
configuration options. If the authentication option is successfully negotiated,
the LCP module initiates authentication after link establishment. This module
performs authentication and the result is communicated to the LCP module.
If authentication succeeds, LCP informs NCP that the PPP link is operational.
If authentication fails, it closes the PPP link and generates an error message.
Password Authentication Protocol (PAP)
The Password Authentication Protocol (PAP) is a simple method for the peer
to establish its identity using a two-way handshake. PAP authentication
occurs only upon initial link establishment. After this phase is complete, the
peer repeatedly sends an ID/Password pair to the authenticator until
authentication is acknowledged or the connection closed.
PAP is not a strong authentication method because passwords are sent over a
circuit in the clear with no protection from playback or repeated trial and error
attacks. The peer controls the frequency and timing of authentication
attempts.