CCNA Complete Guide 2nd Edition.pdf - Cisco Learning Home

- PPP establishes a connection in 3 phases – link establishment (LCP negotiation), authentication
(optional), and network layer protocol negotiation (NCP negotiation). Both ends must agree on
the same parameters to establish a link, and authenticate each other using the authentication
protocol and option negotiated during the LCP negotiation. Authentication must be success prior
to NCP negotiation.
Figure 21-6: Point-to-Point Protocol Stack
- PPP also uses LCP to negotiate the following functions or features:
Function LCP Feature Description
Error Link Quality Monitoring Monitors link quality. PPP LCP at the
Detection (LQM)
receiving end sends messages that describe the
number of correctly received packets and bytes
to the other end. The sending end calculates the
percent of loss. A link can be terminated after a
configured error rate is exceeded.
Looped Link
Detection
(IP, IPX, AppleTalk)
NCP
LCP
HDLC
Sync or Async Media
(Modem, ISDN, Leased Line)
Magic number Endpoints send PPP LCP messages that
include a magic number, which is different for
each endpoint. A looped link is detected when
an endpoint receives an LCP message with its
own magic number instead of the magic
number of the other peer. PPP can be
configured to terminate detected looped links.
Multilink Multilink PPP Allows connections of multiple parallel
channels between 2 routers, and perform load
balancing across the multiple links.
Commonly used in ISDN links.
Authentication Password Authentication
Protocol (PAP) and
Challenge Handshake
Authen. Protocol (CHAP)
151
Network Layer
PPP (Data-Link Layer)
Physical Layer
PPP initiates an authentication process to
verify the identity of the device on the other
end of the serial link. Normally used in dial-up
links (eg: modems, ISDN, and DSL).
Callback PPP Callback The calling router (client) first contacts the
remote router (server) and authenticates itself.
After the authentication process, the remote
router terminates the connection and then
reinitiates a connection to the calling router.
Normally used to minimize the long distance
dialing cost on the client side.
Compression Stacker and Predictor Compresses data at source and reproduces data
at destination. Predictor uses more memory
than Stacker; while Stacker is more CPU
intensive than Predictor.
Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com