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CCNA Semester 4
Chapter 03Chap
ter 03
POINTTO-POINTPOINTTO-POINT
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ObjectivesObjectives
Explain serial communication Identify the demarcation point in a WAN
Describe the functions of the DTE and DCE
Identify the advantages of using PPP
Explain the functions of the Link Control Protocol(LCP) and the Network Control Protocol (NCP)components of PPP
Identify the three phases of a PPP session Explain the difference between PAP and CHAP
List the steps in the PPP authentication process
Configure PPP encapsulation
Configure CHAP and PAP authentication
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Table of ContentTable of Content
1 Serial Point-to-point links
2 PPP Authentication
3 PPP configuration
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SERIAL POINT-TO-POINT LINKSERIAL POINT-TO-POINT LINK
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Introduction To Serial CommunicationIntroduction To Serial Communication
WAN technologies are based on serial
transmission at the physical layerThe signaling methods include Nonreturn to
Zero Level (NRZ-L), High Density Binary 3,(HDB3), and Alternative Mark Inversion (AMI).
011111100110 ..11110 011111100110 ..11110
Transmissionsystem
Transmissionsystem
Physical medium
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Time-division MultiplexingTime-division Multiplexing
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Demarcation PointDemarcation Point
The demarcation point is the point in thenetwork where the responsibility of the service
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DTE-DCEDTE-DCE
The DCE, commonly a modem or CSU/DSU, is thedevice used to convert the user data from the DTEinto a form acceptable to the WAN serviceprovider transmission link.
The DTE-DCE interface for a particular standarddefines the following specifications:
Mechanical/physical Number of pins and connectortype
Electrical Defines voltage levels for 0 and 1
Functional Specifies the functions that are performedby assigning meanings to each of the signaling lines in
Procedural Specifies the sequence of events fortransmitting data
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DTE-DCE (cont.)DTE-DCE (cont.)
The synchronous serial port on a router isconfigured as DTE or DCE depending on the
attached cable
The router end of the shielded serialtransition cable may be a DB-60 connector
The serial end of the smart serial cable is a26-pin connector significantly more compactthan the DB-60 connector.
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HDLC EncapsulationHDLC Encapsulation
HDLC uses synchronous serial transmissionproviding error-free communication betweentwo points.
HDLC defines a Layer 2 framing structure that
allows for flow control and error control usingacknowledgments and a windowing scheme.
Each frame has the same format, whether itis a data frame or a control frame
Standard HDLC does not inherently supportmultiple protocols on a single link
The Cisco HDLC frame allows multiplenetwork layer protocols to share the sameserial link
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Supports only single-protocol environments
HDLC Frame FormatHDLC Frame Format
Uses a proprietary data field to supportmultiprotocol environments
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HDLC Encapsulation (cont.)HDLC Encapsulation (cont.)
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Configuring HDLC EncapsulationConfiguring HDLC Encapsulation
Enter the interface configuration mode of theserial interface.
Then enter the encapsulation hdlccommand to specify the encapsulationprotocol on the interface.
When communicating with a non-Ciscodevice, synchronous PPP is a more viableoption.
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Router(config-if)#encapsulation hdlc
Enables HDLC encapsulation
Uses the default encapsulation on synchronous
serial interfaces
Configuring HDLC EncapsulationConfiguring HDLC Encapsulation
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Troubleshooting A Serial InterfaceTroubleshooting A Serial Interface
show interfaces serial
Serial x is down, line protocol is down
Serial x is up, line protocol is down Serial x is up, line protocol is up (looped)
Serial x is up, line protocol is down (disabled)
Serial x is administratively down, line protocol is
down
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Troubleshooting A Serial InterfaceTroubleshooting A Serial Interface
show controllers
debug serial interface debug frame-relay lmi
debug frame-relay events
debug ppp negotiation
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PPP AUTHENTICATION
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PPP Layered ArchitecturePPP Layered Architecture
PPP uses a layered architecture. A layeredarchitecture is a logical model, design, or blueprintthat aids in communication betweeninterconnecting layers.
PPP provides a method for encapsulating multi-protocol datagrams over a point-to-point link, anduses the data link layer for testing the connection.
PPP is made up of two sub-protocols: Link Control Protocol Used for establishing thepoint-to-point link.
Network Control Protocol Used for configuring thevarious network layer protocols.
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PPP can carry packets from several protocol suitesusing NCP.
PPP controls the setup of several link options using LCP.
PPP Layered ArchitecturePPP Layered Architecture
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PPP Layered Architecture (Cont.)PPP Layered Architecture (Cont.)
- Asynchronous serial- Synchronous serial- High-Speed Serial Interface (HSSI)
- Integrated Services Digital Network (ISDN)
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PPP Layered Architecture (Cont.)PPP Layered Architecture (Cont.)
Authentication Compression Error detection
Multilink PPP Callback
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PPP Layered Architecture (Cont.)PPP Layered Architecture (Cont.)
For every network layer protocol used, aseparateNetwork Control Protocol (NCP) is provided.
NCP includes functional fields containing
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PPP Layered Architecture (Cont.)PPP Layered Architecture (Cont.)
Flag Indicates the beginning or end of aframe
and consists of the binary sequence01111110.
Address Consists of the standard broadcast
address, which is the binary sequence11111111.
Control 1 byte that consists of the binarysequence 00000011,
Protocol 2 bytes that identify the protocol
encapsulated in the data field of the frame. Data 0 or more b tes
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PPP LCP Configuration OptionsPPP LCP Configuration Options
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PPP Session EstablishmentPPP Session Establishment
Two PPP authentication protocols:PAP and CHAP
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Establishing A PPP SessionEstablishing A PPP Session
Link-establishment frames are used to
establish and configure a link. Link-termination frames are used to
terminate a link.
Link-maintenance frames are used to manageand debug a link.
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Establishing A PPP Session: Link-establishment phaseEstablishing A PPP Session: Link-establishment phase
In this phase each PPP device sends LCP framesto configure and test the data link.
LCP frames contain a configuration option fieldthat allows devices to negotiate the use ofoptions such as
maximum transmission unit (MTU),
compression of certain PPP fields,
link-authentication protocol.
If a configuration option is not included in an LCPpacket, the default value for that configurationoption is assumed
This phase is complete when a configurationacknowledgment frame has been sent andreceived.
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Establishing A PPP Session:Establishing A PPP Session: Authentication phaseAuthentication phase
Authentication phase (optional) Afterthe link has been established and theauthentication protocol decided on, the peermay be authenticated.
Authentication, if used, takes place before thenetwork layer protocol phase is entered.
LCP also allows for an optional link-quality
determination test.
The link is tested to determine whether thelink quality is good enough to bring up
network layer protocols
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Establishing A PPP Session:Network layer phaseEstablishing A PPP Session:Network layer phase
In this phase the PPP devices send NCPpackets to choose and configure one or morenetwork layer protocols, such as IP.
Once each of the chosen network layerprotocols has been configured, packets fromeach network layer protocol can be sent over
the linkThe show interfaces command reveals the
LCP and NCP states under PPP configuration
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Passwords sent in clear text
Peer in control of attempts
PPP Authentication ProtocolsPPP Authentication Protocols
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Hash values, not actual passwords, are sent acrosslink.
The local router or external server is in control ofattempts.
Challenge Handshake Authentication ProtocolChallenge Handshake Authentication Protocol
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PPP Authentication Protocols:CHAP OperationPPP Authentication Protocols:CHAP Operation
Sydney Hongkong
Challenge
01IDRandomSydneyUsername PasswordSysney cisco
Melbourne sanhinoon
MD5
Hash #
Response
02IDHash#Hongkong
Username PasswordHongkong cisco
Melbourne sanhinoon
MD5
Hash #
Is Equal?
03IDAck/NackSydney
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PPP Encapsulation And Authentication ProcessPPP Encapsulation And Authentication Process
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CONFIGURING PPP
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Configuring PPPConfiguring PPP
Enable PPP
Router(config)#interface serial 0/0Router(config-if)#encapsulation ppp
To configure compression over PPP, enter the followingcommands:
Router(config-if)#compress [predictor | stac]
Enter the following to monitor the data dropped on thelink, and avoid frame looping:
Router(config-if)#ppp qualitypercentage
The following commands perform load balancing acrossmultiple links:
Router(config-if)#ppp multilink
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Configuring PPP authenticationConfiguring PPP authentication
Step 1: Define username and password to expectfrom remote router
Router(config)#username remote password secret
Secret must be the same at both ends
Step 2: Enable PPP Router(config-if) encapsulation ppp
Step 3: Configure authentication
Router(config-if) Ppp authentication { pap|chap|pap-
chap|chap-pap}
Step 4: if IOS 11.1 or later, PAP must be enableon interface
Router(config-if)ppppap sent-username user
passwordpass
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Configuring PPP and AuthenticationConfiguring PPP and Authentication
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Configuring PPP authentication - PAPConfiguring PPP authentication - PAP
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Configuring PPP authentication - CHAPConfiguring PPP authentication - CHAP
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Verifying The Serial PPP Encapsulation ConfigurationVerifying The Serial PPP Encapsulation Configuration
Houston#sh int serial 1/0:1
Serial1/0:1 is up, line protocol is up
Hardware is DSX1
Internet address is 10.10.10.3/24
MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation PPP, loopback not setKeepalive set (10 sec)
LCP Open
Open: IPCP, CDPCP
Last input 00:00:09, output 00:53:17, output hang never
Last clearing of "show interface" counters 01:09:05Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 164
Queueing strategy: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/1/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)--More--
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Troubleshooting The Serial Encapsulation ConfigurationTroubleshooting The Serial Encapsulation Configuration
right#debug ppp negotiation00:02:28: %LINK-3-UPDOWN: Interface Serial0/0, changed state to
up
00:02:28: Se0/0 PPP: Using default call direction
right(config-i8: Se0/0 PPP: Phase is AUTHENTICATING, by both [0sess, 0 load]
00:02:28: Se0/0 CHAP: O CHALLENGE id 14 len 26 from "right"
00:02:28: Se0/0 CHAP: I CHALLENGE id 17 len 25 from "left"
00:02:28: Se0/0 CHAP: O RESPONSE id 17 len 26 from "right"
00:02:28: Se0/0 CHAP: I RESPONSE id 14 len 25 from "left"
00:02:28: Se0/0 CHAP: O SUCCESS id 14 len 4
00:02:28: Se0/0 CHAP: I SUCCESS id 17 len 4
leftright
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SummarySummary
Explain serial communication Identify the demarcation point in a WAN
Describe the functions of the DTE and DCE
Identify the advantages of using PPP
Explain the functions of the Link Control Protocol(LCP) and the Network Control Protocol (NCP)components of PPP
Identify the three phases of a PPP session
Explain the difference between PAP and CHAP
List the steps in the PPP authentication process
Configure PPP encapsulation
Configure CHAP and PAP authentication
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Q&AQ&A