In preparation of our CCNA exam, we want to make sure we cover the various concepts that we could see on our Cisco CCNA exam. So to assist you, below we will discuss PPP.
PPP: Point-to-Point Protocol Overview
The Point-to-Point Protocol (PPP) provides a standard method for transporting multiprotocol
datagrams over point-to-point links. PPP was originally emerged as an
encapsulation protocol for transporting IP traffic between two peers. It is a data link layer
protocol (layer 2 in the OSI model ) in the TCP-IP protocol suite over synchronous
modem links, as a replacement for the non-standard layer 2 protocol SLIP. However,
other protocols other than IP can also be carried over PPP, including DECnet and
Novell's Internetwork Packet Exchange (IPX).
PPP is comprised of the following main components:
• Encapsulation: A method for encapsulating multi-protocol datagrams. The PPP
encapsulation provides for multiplexing of different network-layer protocols
simultaneously over the same link. The PPP encapsulation has been carefully
designed to retain compatibility with most commonly used supporting hardware.
• Link Control Protocol: The LCP provided by PPP is versatile and portable to a
wide variety of environment. The LCP is used to automatically agree upon the
encapsulation format options, handle varying limits on sizes of packets, detect a
looped-back link and other common misconfiguration errors, and terminate the
link. Other optional facilities provided are authentication of the identity of its peer
on the link, and determination when a link is functioning properly and when it is
• Network Control Protocol: An extensible Link Control Protocol (LCP) for
establishing, configuring, and testing and managing the data-link connections.
• Configuration: Easy and self configuration mechanisms using Link Control
Protocol. This mechanism is also used by other control protocols such as Network
Control Protocols (NCPs).
In order to establish communications over a point-to-point link, each end of the PPP link
must first send LCP packets to configure and test the data link. After the link has been
established and optional facilities have been negotiated as needed by the LCP, PPP must
send NCP packets to choose and configure one or more network-layer protocols. Once
each of the chosen network-layer protocols has been configured, datagrams from each
network-layer protocol can be sent over the link.
The link will remain configured for communications until explicit LCP or NCP packets
close the link down, or until some external event occurs (an inactivity timer expires or
network administrator intervention).
Protocol Structure – PPP (Point to Point Protocol) Frame
8 16 24 40bits Variable 16 – 32 bits
Flag Address Control Protocol Information FCS
• Flag – indicates the beginning or end of a frame, consists of the binary sequence
• Address – contains the binary sequence 11111111, the standard broadcast address.
(Note: PPP does not assign individual station addresses.)
• Control – contains the binary sequence 00000011, which calls for transmission of
user data in an unsequenced frame.
• Protocol – identify the protocol encapsulated in the information field of the frame.
• Information – Zero or more octet(s), contain the datagram for the protocol
specified in the protocol field.
• FCS – Frame Check Sequence (FCS) Field, normally 16 bits. By prior agreement,
consenting PPP implementations can use a 32-bit FCS for improved error
I hope you found this article to be of use and it helps you prepare for your Cisco CCNA certification. Achieving your CCNA certification is much more than just memorizing Cisco exam material. It is having the real world knowledge to configure your Cisco equipment and be able to methodically troubleshoot Cisco issues. So I encourage you to continue in your studies for your CCNA exam certification.