Iap 06   point to point protocol (ppp)
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Iap 06 point to point protocol (ppp)

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  • Purpose: The figure presents an overview of the most popular PPP features.
    Emphasize: The table in the figure lists and describes the various LCP options.
    PPP compression is offered in Cisco’s Compression Control Protocol (CCP).
    RFC 1548 covers the Internet Engineering Task Force (IETF) approved PPP options in detail. RFC 1717 defines Multilink Protocol. RFC 1990, The PPP Multilink Protocol (MP), obsoletes RFC 1717.
    Note: To further enhance security, Cisco IOS Release 11.1 offers callback over PPP. With this LCP option, a Cisco router can act as a callback client or as a callback server.
    The client makes the initial DDR call requests that it be called back, and terminates its initial call. The callback server answers the initial call and makes the return call to the client based on its configuration statements.
    This option is described in RFC 1570.
    Reference: Students will only learn how to configure PAP and CHAP authentication in this course. To learn how to configure the other LCP options, students should attend the Building Cisco Remote Access (BCRAN) course.

Transcript

  • 1. Internet Architecture and Protocols University of education township campus lahore, Pakistan Lecture 06 NCP, PPP Frame Format, Internet Architecture and Protocols, University of education township campus, lahore 1
  • 2. 3. Network Control Protocol • NCP allows the encapsulation of data coming from the network layer protocols into PPP frame • PPP is designed to allow simultaneous use of multiple network layer protocols • PPP provides a way to negotiate network layer options independent to the network layer protocol to be used Internet Architecture and Protocols, University of education township campus, lahore 2
  • 3. Network Control Protocol (NCP) • After the link is established and authentication (if any) is successful, the connection goes to the networking state. • In this state, PPP uses another protocol called Network Control Protocol (NCP). • NCP is a set of control protocols to allow the encapsulation of data coming from network layer protocols into PPP frame. • PPP requires two parties to negotiate not only at the data link layer, but also at the network layer. • Before user data can be sent, a connection must be established at this level. • The set of packets that establish and terminate a network layer connection for IP packets is called IP control protocol (IPCP). Internet Architecture and Protocols, University of education township campus, lahore 3
  • 4. Layering PPP Elements PPP- A data link protocol with network layer services Internet Architecture and Protocols, University of education township campus, lahore 4
  • 5. Internet Architecture and Protocols, University of education township campus, lahore 5
  • 6. PPP Frame Format Internet Architecture and Protocols, University of education township campus, lahore 6
  • 7. PPP Frame Format (1) • Flag – One byte field – It identifies the start and end of the PPP frame – Contains the binary sequence: 0111 1110 • Data – Maximum 1500 bytes – Contains the datagrams for protocol specified in the protocol field • FCS (Frame check sequence) – 2 byte or 4 byte field – Used for error detection using CRC code Internet Architecture and Protocols, University of education township campus, lahore 7
  • 8. PPP Frame Format (2) • Address – One byte field – As the PPP is used for point-to-point connections, not for multipoint connections like LANs, it does not assign individual station addresses – Uses the standard broadcast address value to avoid data link layer addressing (MAC) – It uses the fixed binary sequence: 1111 1111 • Control – One byte field – It specifies that there is no flow and error control – It uses the fixed binary sequence: 0000 0011 Internet Architecture and Protocols, University of education township campus, lahore 8
  • 9. PPP Frame Format (3) • Protocol (Two byte field) – It tells the PPP receiver the upper layer protocol to which the received encapsulated data belongs – Whether the PPP frame carries user data or other information. Codes are defined to identify different protocols Protocol Field Code Protocol Description C02116 LCP C02316 PAP (for authentication) C22316 CHAP (for authentication) 802116 NCP IPCP (IP Datagram for Data) Internet Architecture and Protocols, University of education township campus, lahore 9
  • 10. PPP Stack • The value of protocol field defines the PPP Protocol stack – Although PPP is a data-link layer protocol, PPP uses a stack of other protocols to establish the links, to authenticate the parties involved and to carry the network layer data – Three sets of protocols are defined to make PPP a powerful protocol. • Link Control Protocol (LCP) • Authentication Protocols (PAP, CHAP) • Network Control Protocol (NCP) Internet Architecture and Protocols, University of education township campus, lahore 10
  • 11. PPP Frame Format (4) • Protocol … – It indicates the protocol encapsulated in the data field of PPP frame e.g. • LCP – When PPP is carrying a LCP packet, it is either in establishing or terminating state – No user data is exchanged during this state • Authentication protocol – These protocols are used for authentication – No user data is exchanged during this state • NCP – It allows network layer data encapsulation into PPP frames – User data is exchanged during this state – Thus PPP is a multi-protocol framing method suitable for use over modems Internet Architecture and Protocols, University of education township campus, lahore 11
  • 12. General Operation of PPP • Let us see how the three components of PPP fit together i.e. – Encapsulation – LCP – NCP Internet Architecture and Protocols, University of education township campus, lahore 12
  • 13. PPP – A scenario Internet Architecture and Protocols, University of education township campus, lahore 13
  • 14. A typical Scenario (1) A typical scenario of a home user calling an ISP 1. P.C calls the ISP router via modem 2. After receiving the answer, the physical connection is established between two modems 3. PC sends the router a series of LCP packets in the data portion of PPP frames to configure and (optionally) test the data link connection 4. These LCP packets and their responses select the PPP parameters to be used 5. Then a series of NCP packets are used to configure network layer . 6. NCP frames are used to choose and configure one or more network layer protocols Internet Architecture and Protocols, University of education township campus, lahore 14
  • 15. A typical Scenario … (2) 7. Typically, a PC wants to run a TCP/IP protocol stack, so it needs an IP address 8. ISPs keep a block of IP addresses to be assigned dynamically to each newly attached PC for the duration of its login session 9. The NCP for IP assigns the IP address 10. At this point the PC is now an Internet host and can send and receive IP packets 11. The link will remain configure for communication until explicit LCP or NCP frames close the link or some external event (inactivity timer expires etc.) Internet Architecture and Protocols, University of education township campus, lahore 15
  • 16. A typical Scenario … (3) 12. When the user is finished, the NCP tears down the network layer connection, and frees up the IP address 13. Then LCP shut down the data link layer connection 14. Finally the computer tell the modem to hangup the phone, releasing the physical connection. Internet Architecture and Protocols, University of education township campus, lahore 16
  • 17. Simplified PPP Phase Diagram Internet Architecture and Protocols, University of education township campus, lahore 17
  • 18. PPP Features/Services • Main services of PPP include: – – – – – Encapsulation/Framing Error Detection and Correction Support Multiple Network Layer Protocols Authentication Link Establishment, Termination, Maintenance Internet Architecture and Protocols, University of education township campus, lahore and 18
  • 19. PPP Services… • Encapsulation/Framing – The PPP protocol take a network layer packet and – Encapsulate it within the PPP data link layer frame such that the receiver will be able to identify the start and end of the both data link frame and network layer packet within the frame. • Link Establishment, Maintenance Termination, and – PPP defines how two devices can negotiate the establishment of a link, the exchange of data, and termination of a link. Internet Architecture and Protocols, University of education township campus, lahore 19
  • 20. PPP Services… • Error Detection and Correction – All data link protocols like PPP and HDLC perform error detection. – All these protocols use a field in the trailer usually called frame check sequence (FCS), – FCS verifies whether bit errors occurred during transmission of the frame, if so frame is discarded. – Error recovery is the process that causes retransmission of lost or erred frames. – PPP can perform error correction but by default it is not enabled. Internet Architecture and Protocols, University of education township campus, lahore 20
  • 21. PPP Services… • Support Multiple Network Layer Protocols – PPP supports multiple protocol suites like TCP/IP (IP), Novell’s (IPS), Appletalk etc running over same physical link at the same time. – PPP multiplex different network layer protocols over a single point-to-point connection • Authentication – PPP defines how two devices can authenticate each other. – PPP is designed for use over dial-up links where verification of user identify is necessary. – Authentication means validating the identity of a user who needs to access a set of resources Internet Architecture and Protocols, University of education township campus, lahore 21
  • 22. Phases of PPP Connection… • A PPP connection goes through different phases which are shown in transition state. – – – – – Idle State Establishing State Authenticating State Networking State Terminating State Internet Architecture and Protocols, University of education township campus, lahore 22
  • 23. Phases of PPP Connection… • Idle State – The idle state means that the link is not being used. There is no active carrier, and the link is quiet. • Establishing State – When one of the endpoints starts the communication, the connection goes into establishing state. – In this state, options are negotiated between two parties. If the negotiation is successful, the system goes to the authenticating state (if authentication is required) or directly to the networking state. – The Link Control Protocol packets are used for this purpose. Several packets may exchanged during this phase. Internet Architecture and Protocols, University of education township campus, lahore 23
  • 24. Phases of PPP Connection… • Authenticating State – The authenticating state is optional. – The two endpoints may decide, during the establishing state, not to go through this state. However, if they decide to proceed with authentication, they send several authentication packets. – If the result is successful, the connection goes to the networking state; otherwise it goes to the terminating state. • Networking State – The networking state is heart of the transition states. – When a connection reaches this state, the exchange of user control and data packets can be started. The connection remains in this state until one of the endpoints wants to terminate the connection. Internet Architecture and Protocols, University of education township campus, lahore 24
  • 25. Phases of PPP Connection… • Terminating State – When the connection is in the terminating state, several packets are exchanged between the two endpoints for closing the link. Internet Architecture and Protocols, University of education township campus, lahore 25
  • 26. Data-Link Protocols for Point-to-Point WAN Links • Popular WAN data-link protocols – Serial Line Internet Protocol (SLIP) – High-Level Data Link Control (HDLC) – Point-to-Point Protocol (PPP) Internet Architecture and Protocols, University of education township campus, lahore 26
  • 27. SLIP • Serial Line Internet Protocol – Older protocol – Require no addressing – No authentication – No error checking – Supports only IP – No compression is supported in original Version vs. PPP • Point-to-Point Protocol – New protocol – Supports dynamic IP address assignment – LCP – Error checking – NCP , Carries multiple protocols: IP, IPX, AppleTalk, NetBIOS – Inherently supports compression Internet Architecture and Protocols, University of education township campus, lahore 27
  • 28. HDLC • High Level Data Link Control Protocol – It is both point to point and multipoint protocol – It delivers data on synchronous links only – It provides error detection but does not provide error correction – It does not have protocol type field, so it does not support multiple protocols vs. • Point to Protocol PPP Point – It point to point protocol – It delivers data on both synchronous and asynchronous links – It provides both error detection and error correction – It has a protocol type field so it supports multiple protocols Internet Architecture and Protocols, University of education township campus, lahore 28
  • 29. LCP Features Function LCP Feature Description Error detection Link Quality PPP can take down a link based Monitoring on the percentage of errors on the link. LQM exchanges statistics about lost packets versus sent packets in each direction. When compared to packets and bytes sent, this yields a percentage of erred traffic. The percentage of loss that causes a link to be down is enabled and defined by a configuration setting Internet Architecture and Protocols, University of education township campus, lahore 29
  • 30. LCP Features… Looped link detection Magic numbers Using different magic numbers, routers send messages to each other. If you receive your own magic number, the link is looped. A configuration setting determines whether the link should be taken down when looped Multilink support Multilink PPP Fragments of packets are loadbalanced across multiple links Authenticati on PAP CHAP and Exchanges names and passwords so that device can verify the identity of the device on the other end of the link. Internet Architecture and Protocols, University of education township campus, lahore 30
  • 31. PPP Automatic Login • PPP provides two methods with which logins can be automated – – PAP (Password Authentication Protocol) – CHAP (Challenge-Handshake Authentication Protocol). • Both provide the means for your system to automatically send your login userid/password information to the remote system. Internet Architecture and Protocols, University of education township campus, lahore 31
  • 32. PPP LCP Configuration Options Feature Authentication How It Operates Protocol Require a password PAP Perform Challenge Handshake CHAP Compression Compress data at source; reproduce data at destination Error Detection Monitor data dropped on link Quality Magic Number Avoid frame looping Multilink Load balancing across multiple links Stacker or Predictor Multilink Protocol (MP) Internet Architecture and Protocols, University of education township campus, lahore 32
  • 33. Sample pap/chap configuration hostname RouterA username RouterB password a11 ppp encapsulation ppp authentication pap hostname RouterB username RouterA password a11 ppp encapsulation ppp authentication pap PSTN/ISDN RouterB RouterA “RouterA, mustmat” Accept Internet Architecture and Protocols, University of education township campus, lahore 34
  • 34. Sample pap/chap configuration hostname RouterA username RouterB password a11 interface serial o ip address10.0.1.1 255.255.255.0 encapsulation ppp ppp authentication pap hostname RouterB username RouterA password a11 Interface serial o ip address10.0.1.2 255.255.255.0 encapsulation ppp ppp authentication pap Internet Architecture and Protocols, University of education township campus, lahore 35
  • 35. Verifying PPP P1R1#show interfaces s1 Serial1 is up, line protocol is up Hardware is HD64570 Internet address is 10.1.1.2/24 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255 Encapsulation PPP, loopback not set, keepalive set (10 sec) LCP Open Open: IPCP, CDP, ATALKCP, IPXCP Last input 00:00:04, output 00:00:00, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0 (size/max/drops); Total output drops: 0 Queueing strategy: weighted fair Output queue: 0/64/0 (size/threshold/drops) Conversations 0/4 (active/max active) Reserved Conversations 0/0 (allocated/max allocated) 5 minute input rate 0 bits/sec, 0 packets/sec 5 minute output rate 0 bits/sec, 0 packets/sec 51938 packets input, 1634908 bytes, 0 no buffer --More-- Internet Architecture and Protocols, University of education township campus, lahore 36
  • 36. Putting it all together • The most significant advantage PPP can offer is the automatic login and configuration negotiation at the start of connection • With these features, your PPP software only needs to know your login userid/password and the telephone number of your service provider. • The software can then dial-up into your service provider and figure out everything else on its own. • At this present point in time, PPP is generally not as widely available as SLIP. It should gain more acceptance in the time to come Internet Architecture and Protocols, University of education township campus, lahore 37