CCNA Exp4 - Chapter02 - PPP

8/3/2019 CCNA Exp4 - Chapter02 - PPP

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Chapter 2 – PPP

CCNA Ex loration 4.0

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Introduction

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Serial Point-to-Point Links




Introducing Serial Communications


• Computers make use of relatively short parallel connections betweeninterior components, but use a serial bus to convert signals for mostexternal communications.





• In a parallel connection, it is wrong to assume that the 8 bits leaving the senderat the same time arrive at the receiver at the same time. Rather, some of thebits get there later than others. This is known as clock skew.





• Parallel wires are physically bundled in a parallel cable, and signals can imprintthemselves on each other. The possibility of crosstalk across the wiresrequires more processing, especially at higher frequencies.





• Serial Communication Standards – All long-haul communications and most computer networks use serial connections,

because the cost of cable and synchronization difficulties make parallel connectionsimpractical.

– The most significant advantage is simpler wiring. Also, serial cables can be longerthan parallel cables, because there is much less interaction (crosstalk) among theconductors in the cable.





TDM


• Time Division Multiplexing – Bell Laboratories invented time-division multiplexing (TDM) to maximize

the amount of voice traffic carried over a medium.

– TDM divides the bandwidth of a single link into separate channels or timeslots.

– TDM transmits two or more channels over the same link by allocating adifferent time interval (time slot) for the transmission of each channel.



TDM


• Statistical Time Division Multiplexing (STDM) – STDM uses a variable time slot length allowing channels to compete for

any free slot space. It employs a buffer memory that temporarily stores thedata during periods of peak traffic.

– STDM does not waste high-speed line time with inactive channels usingthis scheme.





TDM Examples




Demarcation Point




DTE-DCE


• The CPE, which is generally a router, is the DTE. The DTE could alsobe a terminal, computer, printer, or fax machine if they connect directlyto the service provider network.

• The DCE, commonly a modem or CSU/DSU, is the device used toconvert the user data from the DTE into a form acceptable to the WANservice provider transmission link. This signal is received at the remoteDCE, which decodes the signal back into a sequence of bits. Theremote DCE then signals this sequence to the remote DTE.



Cable Standards


• The DTE/DCE interface for a particular standard defines the following

specifications: – Mechanical/physical - Number of pins and connector type – Electrical - Defines voltage levels for 0 and 1 – Functional - Specifies the functions that are performed by assigning

meanings to each of the signaling lines in the interface – Procedural - Specifies the sequence of events for transmitting data



Cable Standards




Cable Standards




Parallel to Serial Conversion


• Your PC also has a Universal Asynchronous Receiver/Transmitter (UART) chip

on the motherboard. Since the data in your PC flows along parallel circuits, theUART chip converts the groups of bits in parallel to a serial stream of bits.• To work faster, a UART chip has buffers so it can cache data coming from the

system bus while it processes data going out the serial port.

• The UART is the DTE agent of your PC and communicates with the modem orother serial device, which, in accordance with the RS-232C standard, has a

complementary interface called the DCE interface.



HDLC Encapsulation


• HDLC - The default encapsulation type on point-to-point connections,dedicated links, and circuit-switched connections when the link usestwo Cisco devices. HDLC is now the basis for synchronous PPP usedby many servers to connect to a WAN, most commonly the Internet.



HDLC Encapsulation




Configuring HDLC Encapsulation


• Cisco HDLC is the default encapsulation method used by Ciscodevices on synchronous serial lines.• You use Cisco HDLC as a point-to-point protocol on leased lines

between two Cisco devices. If you are connecting to a non-Ciscodevice, use synchronous PPP.



Troubleshooting a Serial Interface


• You can identify any of the following five possible problem states in the interface statusline:

1. Serial x is down, line protocol is down2. Serial x is up, line protocol is down3. Serial x is up, line protocol is up (looped)4. Serial x is up, line protocol is down (disabled)

5. Serial x is administratively down, line protocol is down









• The command syntax varies, depending on the platform. Cisco 7000series routers use a cBus controller card for connecting serial links.With these routers, use the show controllers cbus command.




















• Activity 2.1.7.3






















Introducing PPP

• What is PPP? – Cisco HDLC is the default serial

encapsulation method when youconnect two Cisco routers.

– When you need to connect to a

non-Cisco router, you should usePPP encapsulation. – PPP establishes a direct

connection using serial cables,phone lines, trunk lines, cellulartele hones s ecialized radio links


or fiber-optic links.

– There are many features notavailable in HDLC:

• The link quality managementfeature monitors the quality ofthe link. If too many errors aredetected, PPP takes the link

down.• PPP supports PAP and CHAPauthentication. This feature isexplained and practiced in alater section.

PPP contains 3 main components:

1. HDLC protocol for encapsulatingdatagrams over point-to-point links.

2. Extensible Link Control Protocol(LCP) to establish, configure, and testthe data link connection.

3. Family of Network Control Protocols(NCPs) for establishing andconfiguring different network layer

protocols.



PPP Layered Architecture


• At the physical layer, you can configure PPP on a range of interfaces,

including: – Asynchronous serial – Synchronous serial – HSSI – ISDN



PPP Architecture - Link Control Protocol Layer


• The LCP provides automatic configuration of the interfaces at each end, including:

– Handling varying limits on packet size – Detecting common misconfiguration errors – Terminating the link – Determining when a link is functioning properly or when it is failing

• PPP also uses the LCP to agree automatically on encapsulation formats (authentication,compression, error detection) as soon as the link is established.



PPP Architecture - Network Control Protocol Layer




PPP Frame Structure




Establishing a PPP Session


• Phase 1: Link establishment and configuration negotiation

• Phase 2: Link quality determination (optional)

• Phase 3: Network layer protocol configuration negotiation



Extra: PPP Session Establishment (Detail)


1. Link establishment - (LCPs)

2. Authentication - Optional (LCPs)

3. Link quality determination - Optional (LCPs)4. Network layer protocol configuration (NCPs)

5. Link termination (LCPs)

C



Establishing a Link with LCP


• LCP operation uses three classes of LCP frames to accomplish the work of each of theLCP phases: – Link-establishment frames establish and configure a link (Configure-Request,

Configure-Ack, Configure-Nak, and Configure-Reject) – Link-maintenance frames manage and debug a link (Code-Reject, Protocol-Reject,

Echo-Request, Echo-Reply, and Discard-Request)

– Link-termination frames terminate a link (Terminate-Request and Terminate-Ack)

E bli hi Li k i h LCP



Establishing a Link with LCP


LCP P k t



LCP Packet


LCP P k t



LCP Packet


PPP Configuration Options





• PPP can be configured to support various functions including:1. Authentication using either PAP or CHAP2. Compression using either Stacker or Predictor3. Multilink which combines two or more channels to increase the

WAN bandwidth






NCP Explained



NCP Explained


NCP Explained



NCP Explained



NCP Explained



NCP Explained



NCP Explained



NCP Explained











• PPP may include the following LCP options: – Authentication – Compression – Error Detection – Multilink – PPP Callback

PPP Configuration Commands









• Example 1: Enabling PPP on an Interface – R3#configure terminal – R3(config)#interface serial 0/0

– R3(config-if)#encapsulation ppp• Example 2: Compression – R3(config)#interface serial 0/0 – R3(config-if)#encapsulation ppp


– R3(config-if)#compress [predictor | stac]

• Example 3: Link Quality Monitoring – R3(config)#interface serial 0/0 – R3(config-if)#encapsulation ppp – R3(config-if)#ppp quality 80

• Example 4: Load Balancing Across Links – Router(config)#interface serial 0/0 – Router(config-if)#encapsulation ppp – Router(config-if)#ppp multilink



Extra: More Information on Compression



Extra: More Information on Compression

Important notes on compression:

– The highest compression ratio is usually reached with highly compressible

text files.

– Already compressed files such as JPEG graphics or MPEG files, or filesthat were compressed with software such as PKZIP or StuffIt, are onlycompressed 1:1, or even less.

–


transferring the data without compression.

– Compressing data can cause performance degradation because it issoftware, not hardware compression.

– Compression can be CPU or memory intensive.

– Predictor is more memory intensive and less CPU intensive, whereasStacker and MPPC are more CPU intensive and less memory intensive.

Memory intensive means that an extra memory allowance is required.

Extra: Enable Link Quality Monitoring (LQM)



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• Link Quality Monitoring (LQM) is available on all serial interfaces runningPPP. LQM will monitor the link quality, and if the quality drops below aconfigured percentage, the router shuts down the link.

• The percentages are calculated for both the incoming and outgoingdirections. – The outgoing quality is calculated by comparing the total number of

packets and bytes sent with the total number of packets and bytes


.

– The incoming quality is calculated by comparing the total number ofpackets and bytes received with the total number of packets andbytes sent by the destination peer.

• When LQM is enabled, Link Quality Reports (LQRs) are sent, in place ofkeepalives, every keepalive period. All incoming keepalives areresponded to properly. If LQM is not configured, keepalives are sentevery keepalive period and all incoming LQRs are responded to with anLQR.

• LQR is specified in RFC 1989, PPP Link Quality Monitoring , by WilliamA. Simpson of Computer Systems Consulting Services.

Verifying a Serial PPP Encapsulation Configuration




Troubleshooting PPP Encapsulation



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g p












Configuring PPP


with Authentication

PPP Authentication Protocols




• The authentication phase of a PPP session is optional. If used, you canauthenticate the peer after the LCP establishes the link and choose theauthentication protocol. If it is used, authentication takes place beforethe network layer protocol configuration phase begins.

Password Authentication Protocol (PAP)




Challenge Handshake Authentication Protocol (CHAP)



• Initiating CHAP


• Responding CHAP

•• Completing CHAP

PPP Encapsulation and Authentication Process







Configuring PPP with Authentication







Example: Configuring PAP



172.25.3.0/24

Serial .1/S0.2/S0

DCEDTE

hostname SantaCruzusername HQ password HQpass

interface Serial0

ip address 172.25.3.2 255.255.255.0

hostname HQusername SantaCruz password SantaCruzpass

interface Serial0

ip address 172.25.3.1 255.255.255.0


Notes:

- sent-username and password must match remote username and password.

- Passwords are case-sensitive, but usernames are not.

- Hostnames are not involved.

encapsulation ppp

ppp authentication pap

ppp pap sent-username SantaCruz password SantaCruzpass

encapsulation ppp


ppp pap sent-username HQ password HQpass

Extra: One-way PAP authentication



(config)# hostname RA

(config)# interface serial 0

encapsulation ppp


ppp pap sent-username RA-X password CISCO-X

(config)# hostname RB

(config)# username RA-X password CISCO-X


encapsulation ppp


Extra: Two-way PAP authentication




(config)# username RB-X password CISCO-B


encapsulation ppp



ppp pap sent-username RA-X password CISCO-A

(config)# hostname RB

(config)# username RA-X password CISCO-A


encapsulation ppp


ppp pap sent-username RB-X password CISCO-B

Example: Configuring CHAP



172.25.3.0/24

Serial .1/S0.2/S0

DCEDTE

hostname SantaCruzusername HQ password boardwalk

ppp chap hostname SantaCruz (optional)

interface Serial0

hostname HQusername SantaCruz password boardwalk

ppp chap hostname HQ (optional)

interface Serial0


Notes:

- Hostnames are involved unless the ppp chap hostname command is used, and

must match remote router’s username command (not case-sensitive).

- Passwords are case-sensitive and must match

ip address 172.25.3.2 255.255.255.0

encapsulation ppp

ppp authentication chap

ip address 172.25.3.1 255.255.255.0

encapsulation ppp

ppp authentication chap

Extra: One-way CHAP authentication



(config)# hostname RA-X

(config)# username RB password CISCO(config)# interface serial 0

encapsulation pppOR



(config)# interface serial 0encapsulation pppppp chap hostname RA-Xppp chap password CISCO

(config)# hostname RB(config)# username RA-X password CISCO(config)# interface serial 0

encapsulation pppppp authentication chap

Troubleshooting a PPP Configuration with Authentication




• In the last line, the code = 4 means a failure has occurred. Other code values are as

follows: – 1 = Challenge – 2 = Response – 3 = Success – 4 = Failure

Extra: Configuring PPP Multilink (MLP)



Router(config)#interface serial 0/0

Router(config-if)#encapsulation ppp

Router(config-if)# ppp multilink


• In some environments, it may be necessary to bundle multiple seriallinks to act as single link with aggregated bandwidth.

• Multilink PPP provides load balancing over the router interfaces thatPPP uses.

Extra: Configuring PPP Multilink



hostname SantaCruz

multilink Virtual-Template 1

interface loopback 0

ip address 192.168.1.1 255.255.255.0

hostname HQ

multilink Virtual-Template 1

interface loopback 0

ip address 192.168.1.2 255.255.255.0


interface Virtual-Template1

ip unnumbered loopback0 ppp multilink

interface Serial0

no ip address

encapsulation ppp

ppp multilink

interface Serial1

no ip address

encapsulation ppp

ppp multilink

interface Serial2

no ip address

encapsulation ppp

ppp multilink

interface Virtual-Template1

ip unnumbered loopback0 ppp multilink

interface Serial0

no ip address

encapsulation ppp

ppp multilink

interface Serial1

no ip address

encapsulation ppp

ppp multilink

interface Serial2

no ip address

encapsulation ppp

ppp multilink

Extra: Configuring PPP Multilink



(config)# interface Multilink 1ip address 1.2.3.4 255.255.255.0


(config)# interface Serial 0/0

no ip addressencapsulation pppppp multilinkppp multilink group 1

(config)# interface Serial 0/1

no ip addressencapsulation ppp

ppp multilinkppp multilink group 1

Labs




Summary




Documents

CCNA Exp4 - Chapter02 - PPP