Iap 05   point to point protocol (ppp)
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Iap 05   point to point protocol (ppp) Iap 05 point to point protocol (ppp) Presentation Transcript

  • Internet Architecture and Protocols University of education township campus lahore, Pakistan Lecture 05 PPP (POINT TO POINT PROTOCOL) Internet Architecture and Protocols, University of education township campus, lahore 1
  • Lecture Objectives • WAN Basics – Three types of WAN Services • Introduction to Point-to-Point protocol (PPP) • Basic Components of PPP – Encapsulation, LCP, NCP • PPP Frame Format • PPP Authentication – PAP, CHAP • General Operation of PPP • PPP Services Internet Architecture and Protocols, University of education township campus, lahore 2
  • WAN Point-to-Point Link Internet Architecture and Protocols, University of education township campus, lahore 3 View slide
  • WAN Services Term Description Leased lines A dedicated, always on circuit between two end points. The service provider just passes a constant rate bit stream. Generally is more expensive than packet switching today Circuit switched/ dial Provide dedicated bandwidth between two points, but only for the duration of the call. Typically used as a cheaper alternative to leased lines, particularly when connectivity is not needed all the time. Also useful for backup when a leased line or packet-switched service fails Packetswitched Provides virtual circuits between pairs of sites, with contracted traffic rates for each VC. Each site’s physical connectivity consists of a leased line from the site to a device in the provider’s network. Generally cheaper than leased lines. Internet Architecture and Protocols, University of education township campus, lahore 4 View slide
  • WAN Data-Link Protocols for Point-to-Point Links Leased line Circuit-switched Packet-switched Internet Architecture and Protocols, University of education township campus, lahore 5
  • An Overview of Wide-Area Services Call Setup (SS7 or other) C A B E Time-Division Multiplexed Circuits (56/64 kbps or T1/E1) Central Office (CO) Basic Telephone Service CO X.25/Frame Relay X.25 / Frame Relay Networks Networks Basic Telephone Service • A simplified look inside the WAN cloud • The router also uses a WAN central office Internet Architecture and Protocols, University of education township campus, lahore 6
  • PPP over the Internet • Today, million of Internet users who need to connect their home PCs to the server of an ISP use PPP • The Internet needs a PPP for a variety of purposes, including router-to-router traffic (leased line) and home-user to ISP (dial-up) traffic. • Majority users have a traditional modem, DSL modem or a cable modem which connects them to the Internet through a Telephone line or a TV cable connection. • These lines provide a physical link, but to control and manage the transfer of data, there is a need of PPP Internet Architecture and Protocols, University of education township campus, lahore 7
  • PPP over the Internet • For both connections, router-to-router (leased line connections) and home-user to ISP (dial-up connections) some data link protocol is required on the line for: – Framing or encapsulation – Error control and other data link layer functions • If two devices are directly connected to each other, then they are said to be in point-to-point configuration • Point-to-point protocol is a data link layer protocol which is used to control the communication over such links Internet Architecture and Protocols, University of education township campus, lahore 8
  • Definition - PPP • PPP is defined in 1661. • It originally emerged as an encapsulation protocol for transporting IP traffic over point-topoint links. • PPP also established a standard for – assigning and managing IP addresses – asynchronous and synchronous encapsulation – network protocol multiplexing – link configuration & link quality testing – error detection, option negotiation Internet Architecture and Protocols, University of education township campus, lahore 9
  • PPP Components • Main components of PPP include: – Encapsulation/Framing – Link Control Protocol (LCP) – Network Control Protocol (NCP) • These components help PPP to define the frame formats to be exchanged, how the 2 devices will negotiate with each other to establish a link and for exchanging the data, how the link is configured and terminated. Internet Architecture and Protocols, University of education township campus, lahore 10
  • 1. Encapsulation • It is a method for encapsulating datagrams of network layer over serial links • A framing mechanism defines the boundaries of the start and end of the PPP frame • It also helps in error detection Internet Architecture and Protocols, University of education township campus, lahore 11
  • Encapsulation… Internet Architecture and Protocols, University of education township campus, lahore 12
  • 2. Link Control Protocol • LCP is used to establish, configure and test the data link connections • Its main purpose is: – to bring the lines up, test them – negotiate options – and bringing them gracefully down again when they are no longer needed • It supports synchronous and asynchronous circuits • LCP configuration options include: – Maximum frame size or MTU (maximum transmission unit) – Authentication protocol specifications (if any) – Options to skip control and address fields of PPP frame • PPP negotiates configuration parameters at the start of the connection using LCP. Internet Architecture and Protocols, University of education township campus, lahore 13
  • LCP packet encapsulated in a frame Internet Architecture and Protocols, University of education township campus, lahore 14
  • LCP Phase: Common options Option Default Maximum receive unit 1500 Authentication protocol None Protocol field compression Address and compression control Off field Internet Architecture and Protocols, University of education township campus, lahore Off 15
  • Link Control Protocol (LCP) • LCP is responsible for establishing, maintaining, configuring, and terminating links. • It also provides negotiation mechanisms to set options between the two endpoints. Both endpoints of the link must reach an agreement about the options before the link can be established. • When PPP is carrying a LCP packet, it is either in establishing or terminating state • No user data is exchanged during this state • All LCP packets are carried in the data field of the PPP frame Internet Architecture and Protocols, University of education township campus, lahore 16
  • Link Control Protocol (LCP) • LCP frames are categorized into 3 classes – Link establishment frames – Link terminating frames – Link maintenance frames • Options – There are many options that can be negotiated between the two endpoints. – Options are inserted in the information field of the configuration packets Internet Architecture and Protocols, University of education township campus, lahore 17
  • LCP packets and their codes Code Packet Type Description 0116 Configure-request Contains the list of proposed options and their values 0216 Configure-ack Accepts all options proposed 0316 Configure-nak Announces that some options are not acceptable 0416 Configure-reject Announces that some options are not recognized 0516 Terminate-request Requests to shut down the line 0616 Terminate-ack Accepts the shut down request 0716 Code-reject Announces an unknown code 0816 Protocol-reject Announces an unknown protocol 0916 Echo-request A type of hello message to check if the other end is alive 0A16 Echo-reply The response to the echo-request message 0B16 Discard-request A request to discard the packet Internet Architecture and Protocols, University of education township campus, lahore 18
  • PPP Authentication… Internet Architecture and Protocols, University of education township campus, lahore 19
  • Authentication Protocols • The term authentication refers to a set of security functions that help one device ensure that it is communicating with the correct other device • PPP use two authentication protocols – Password Authentication Protocol (PAP) – Challenge Handshake Authentication Protocol (CHAP) Internet Architecture and Protocols, University of education township campus, lahore 20
  • Password Authentication Protocol • Password Authentication Protocol (PAP) – PAP sends the username and password in clear text. – The user who wants to access a system sends username and password – The system checks the validity of the username and password and either accepts or denies connection. – For those systems that require greater security, PAP is not enough; a third party with access to the link can easily pick up the password and access the system resources Internet Architecture and Protocols, University of education township campus, lahore 21
  • Password Authentication Protocol Internet Architecture and Protocols, University of education township campus, lahore 22
  • Selecting a PPP Authentication Protocol Internet Architecture and Protocols, University of education township campus, lahore 23
  • Challenge Handshake Authentication Protocol • Challenge Handshake Protocol (CHAP) Authentication – It is a three handshaking authentication protocol that provides greater security that PAP. – In this method the password is kept secret, it is never sent online. – The system sends to the user a challenge packet containing a challenge value, usually a few byte. – The user applies a predefined function (Message Digest-5, one way hash function) that takes the challenge value and the user’s own password and creates a result. The user sends the result in the response packet to the system Internet Architecture and Protocols, University of education township campus, lahore 24
  • CHAP… • Challenge Handshake Protocol (CHAP)… Authentication – The system does the same. It applies the same function to the password of the user (known to the system) and the challenge value to create a result. If the result created the same as the result in the response packet, access is granted; otherwise it is denied – CHAP is more secure than PAP, especially if the system continuously changes the challenge value. Even if the intruder learns the challenge value and the result, the password is still secret. – CHAP authentication is difficult to break Internet Architecture and Protocols, University of education township campus, lahore 25
  • CHAP… Internet Architecture and Protocols, University of education township campus, lahore 26
  • Selecting a PPP Authentication Protocol Internet Architecture and Protocols, University of education township campus, lahore 27