introduction to ppp. using dial-up modems for packet-oriented- networking (i.e connecting to the...
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Introduction to PPP
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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
History
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SLIP - Serial Line Internet Protocol Defined in the early 80`s Purpose
extending TCP/IP networking with dial-up serial connection
Usersunix users at the beginning and PC users later
Advantages Very simple protocol Easy implementation
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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
address
Is not approved internet standard
Does not provide any form of authentication
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PPP – design principles
Support multiple network protocols Link configuration Error detection Establishing network addresses Authentication Extensibility
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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
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HDLC
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
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3 variable-length fields Address – intended for multidrop links Control – specifies the type of message transmitted Information – content transferred by the top level
application 1 fixed-length field
Check
HDLC – frame format
address control information check
HDLC frame
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Establishing PPP communication requires
transitioning a connection through several
states
Some of these operations are done by
LCP and some by NCP
PPP state machine
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10
Point-to-Point Protocol
Point-to-Point Protocol (PPP) is a byte-oriented protocol developed in 1990s as a replacement
for SLIP .The packet begins and ends with a flag “01111110”.
Therefore, it suffers the transparency problem.CRC-16 for error control
Supports network layer protocols other than just Internet protocol.
Message length is up to 1500 bytes.
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Dead Establish
Network
terminate Authenticate
PPP state machine
opened
Success / None
down
closing
fail
fail
up
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PPP – frame format
Protocoltype 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
dataprotocolflag addr control padding check
PPP frame
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LCP
Purposes Link establishment Link maintenance Link termination
Optional operations Link quality determination Authentication
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LCP - packets
There are 3 classes of LCP packets: Link configuration
configure-request, configure-ack, configure-nak & configure-reject
Link terminationterminate-request & terminate-ack
Link monitoringcode-reject, protocol-reject, echo-request, echo-reply & discard-request
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NCP
PurposeConfiguring 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
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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
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PPP – unsupported options Flow control
Any PPP frame sent that overflows thereceiver's buffer are lost
Error correctionPPP includes only Frame Check Sequence (CRC)
Re-sequencingPPP assumes all frames, sent and received, retain their original intended order
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Tunneling - definitionThe process of running one network protocol
on top of another.
Common use: VPN (Virtual Private Network) Tunneling method
Extending the link between the HDLC driverand the rest of PPP over a separate network
PPP tunneling protocolsL2TP, L2F, PPTP & ethernet (PPPoE)
Tunneling & PPP
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Tunneling & PPP
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THE MIDDLE
Next: PPP security
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Internet layered architechture
Application
Transport
Network
Data Link
Physical Media, clocking and synchronization
Data link operations (???)
Forwarding and route discovery
Port and traffic management
End-user application
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Data link protocol
Defintionmanages node-to-node transfer of data between
two directly connected machines.
Operations Error detection and correction (depends on the protocol) Addressing (in LANs) Frame-level synchronization between sender and
receiver Flow control Maintaining awareness of link conditions
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HDLC`s family
HDLC
LAPB)x. 25(
LAPM)v. 42(
LAPD)ISDN(
LLC)LANs(
SDLC)SNA(
LAPX)teletex(
ESF)T1(
MTP-2)SS7(
LAPDm)GSM(
LAPF)frame-relay(
PPP)many(
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PPP – a layered protocol
Application
Transport
Network
NCP
LCP
HDLC
Physical
Data LinkPPP
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PPP – design principles Support multiple network protocols
Link configuration Error detection Establishing network addresses Authentication Extansibility
Not limited to the internet and other TCP/IP networks, I.e: IPX/SPX and IPv6
Includes nagotiation mechanisms for establishing communication parameters betweens two PPP peersDetects datagrams corruption upon reception and discards such corrupted dataSets network addresses necessary for the datagrams routing
Supports authentication between peers before useful communication begins
Yet, maintains backward compatibility
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HDLC(High-level Data Link Protocal)
1.It is a bit-oriented synchronous protocol.
2.HDlC is Data Link Layer Protocl and it is a Communication Protocol .
3.HDLC is Cisco prperitry prtocal and Devloped by ISO and it is delovped out of IBM'S SDLC(Synchronous Data Link Protocol)
4.HDLC is superset of SDLC.
5.It supports only Synchronous comunication.
6.It has 3 transfer modes of Normal Response mode (NRM),Asynchronous Response Mode(ARM),Asynchronous Balanced Mode(ABM).
PPP(Point To Point Protocol)
1.It is a byte-oriented synchronous protocol.
2.It is used for direct Comunication between 2 nodes,it has no transfer mode like HDLC.
3.PPP is type of HLDC .
4.It supports encryption,authentication and Comparision.
5.Authenticaion Support by PAP (password authenticaion protocol) and also by CHAP(Challange Handshake Protocal).
6.It is not a Cisco Proprietary.