Introduction to PPP by kmb15358

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									Introduction to PPP

                Sharon Katz
   Dial-up file transfer protocol
    Early 80`s: PC users
    Dial-up networking begin to communicate
     In the unix transfer protocols:
     through fileworld TCP/IP vs. file transfer protocols
         X-Modem
     Telecommunication technologies:
         Y-Modem
                         3MB and protocols
          Local networks: Asymetric10MB ethernets.
         Z-Modemcommunication:
         Distance
                 Leased lines
                 Primitive dial-up modems
   Using dial-up modems for packet-oriented-
    networking (I.e connecting to the internet)
    requires a data-link layer protocol
   widely-spread protocols:
       SLIP
       PPP
SLIP - Serial Line Internet Protocol
   Defined in the early 80`s
   Purpose
    extending TCP/IP networking with
    dial-up serial connection
   Users
    unix users at the beginning and PC users later
   Advantages
       Very simple protocol
       Easy implementation
SLIP - Serial Line Internet Protocol
   Disadvantages
       Does not support error detction and correction
       Supports only IP (and not IPX/SPX etc`)
       Requires advance knowledge of the peer`s IP
       Is not approved internet standard
       Does not provide any form of authentication
PPP – design principles
   Support multiple network protocols
   Link configuration
   Error detection
   Establishing network addresses
   Authentication
   Extensibility
PPP – a layered protocol
   PPP relies on another DLP – HDLC – to
    perform some basic operations
   After the initial handshake, PPP executes
    its own handshake
   PPP itself consists of two protocols:
       LCP – Link Control Protocol
       NCP – Network Control Protocol
   Definition
       High-level Data Link Control, Bit-oriented link protocol
        published by ISO
       foundation for other protocols (examples      )

   Operations
       1st stage – frame formation
       2nd stage – medium-dependant frame transmission
HDLC – frame format
                            HDLC frame
             address control information       check

   3 variable-length fields
       Address – intended for multidrop links
       Control – specifies the type of message transmitted
       Information – content transferred by the top level
   1 fixed-length field
       Check
PPP state machine
   Establishing PPP communication requires
    transitioning a connection through several
   Some of these operations are done by
    LCP and some by NCP
PPP state machine

      Dead                 Establish

  down                          opened
    terminate             Authenticate

 closing                        Success / None
PPP – frame format

flag      addr control protocol        data      padding   check
                         PPP frame

   Protocol
     type of information in data/padding field
     (I.e: IP, IPCP, LCP, CHAP etc`)
   Data/Padding
     data for the upper layer protocols or PPP
     control packets
   Purposes
       Link establishment
       Link maintenance
       Link termination
   Optional operations
       Link quality determination
       Authentication
LCP - packets
   There are 3 classes of LCP packets:
       Link configuration
         configure-request, configure-ack,
         configure-nak & configure-reject
       Link termination
         terminate-request & terminate-ack
       Link monitoring
         code-reject, protocol-reject, echo-request,
         echo-reply & discard-request
LCP – packet format

 PPP frame code    ID   length   Data   PPP frame

   Code – type of LCP packet (configure-ack
   ID – request-response matching ID
   Length – of the LCP packet
   Data – the LCP packet
LCP Options
   MRU determination
   Magic number selection
   Authentication Protocol
   Escaped characters map
   Purpose
    Configuring the network layer protocol.
    There exists a separate NCP for each
    network layer protocol
   Negotiation process
    Same message formats, code numbers
    and state machines as LCP
IPCP – IP Control Protocol
   Purpose
       TCP/IP matching NCP
       Establishes, configures and terminates the
        TCP/IP network layer protocol
   Options
       IP-Compression protocol – I.e Van-Jacobson
        (VJ) compressed TCP/IP
       IP address – allows dynamic IP configuration
       DNS & NBNS address
IPCP – packet format

                PPP frame

  0x7E 0xFF 0x03 0x8021               data      check

              Code   ID      length      IPCP data
PPP – unsupported options
   Flow control
    Any PPP frame sent that overflows the
    receiver's buffer are lost
   Error correction
    PPP includes only Frame Check
    Sequence (CRC)
   Re-sequencing
    PPP assumes all frames, sent and received,
    retain their original intended order
Tunneling & PPP
   Tunneling - definition
    The process of running one network protocol
    on top of another.
    Common use: VPN (Virtual Private Network)
   Tunneling method
    Extending the link between the HDLC driver
    and the rest of PPP over a separate network
   PPP tunneling protocols
    L2TP, L2F, PPTP & ethernet (PPPoE)
Tunneling & PPP
      Next: PPP security
Internet layered architechture

  Application   End-user application

  Transport     Port and traffic management

   Network      Forwarding and route discovery

  Data Link     Data link operations (???)

   Physical     Media, clocking and synchronization
Data link protocol
  manages node-to-node transfer of data between
  two directly connected machines.
     Error detection and correction (depends on the protocol)
     Addressing (in LANs)
     Frame-level synchronization between sender and
     Flow control
     Maintaining awareness of link conditions
HDLC`s family

LAPM      LAPB          LAPD       LLC     SDLC           LAPX
(v. 42)   (x. 25)      (ISDN)    (LANs)    (SNA)        (teletex)

                    ESF     MTP-2      LAPDm        LAPF         PPP
                    (T1)    (SS7)       (GSM)   (frame-relay)   (many)
PPP – a layered protocol
Data Link                  LCP

PPP – design principles
   Support multiple network protocols
   Not limited to the internet
    Link configuration and other TCP/IP networks,
    I.e: IPX/SPX and IPv6
   Includes nagotiation
    Error detection mechanisms for establishing
    communication parameters betweens two PPP peers
   Establishing network addresses and
    Detects datagrams corruption upon reception
    discards such corrupted data
   Authentication
    Sets network addresses necessary for the datagrams
   Extansibility
    Supports authentication between peers before useful
    communication begins compatibility
    Yet, maintains backward

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