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Point-to-Point Protocol (PPP)
Point-to-Point Protocol (PPP) is a Data Link layer protocol that can be used over either asynchronous
serial (dial-up) or synchronous serial (ISDN) media. It uses the LCP (Link Control Protocol)
to build and maintain data link connections. Network Control Protocol (NCP) is used to allow
multiple Network layer protocols (routed protocols) to be used on a point-to-point connection.
Since HDLC is the default serial encapsulation on Cisco serial links and it works great, when
would you choose to use PPP? The basic purpose of PPP is to transport layer 3 packets across a
Data Link layer point-to-point link. It is nonproprietary, which means that if you don’t have all
Cisco routers, PPP would be needed on your serial interfaces—the HDLC encapsulation would
not work because it is Cisco proprietary. In addition, since PPP can encapsulate several layer 3
routed protocols and provide authentication, dynamic addressing, and callback, this may be the
encapsulation solution of choice for you over HDLC.
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