CCNA CHAPTER 9 BY jetarvind kumar madhukar

Release 16/07/2009 Jetking Infotrain Ltd.

Establishing Serial Point-to-Point Connection

Chapter 9

Release 16/07/2009Jetking Infotrain Ltd.

Chapter Objectives

Explain wide area network Explain data-link protocols of point-to-point

leased lines Explain HDLC Explain PPP


Recall - I ACL are the statements, which are grouped together

by using a name or number ACLs supports the following types:

Standard ACL Extended ACL

You can use the access-list command to create an ACL. The syntax to create an ACL is: access-list ACL_# permit|deny conditions


Recall - II

Wildcard masks can be used for matching a range of IP addresses in ACL, instead of manually entering it

A wildcard is similar to an inverted subnet mask the extended ACL filters the source and destination

IP address, IP protocols such as IP, TCP, UDP , ICMP etc. and protocol information such as port numbers or message types


Wide Area Network

The terms and components of WAN are: Data Communications Equipment (DCE) Data Terminal Equipment (DTE) Customer Premises Equipment (CPE) Demarcation point Toll network Central Office (CO) switch Local loop


Wide Area Network (WAN)


Types of WAN

WANs are available in four types, based on the distance covered and the equipment used

The four types of WAN are: Leased-Lines Connection Circuit-Switched Connection Packet-Switched Connections Cell-Switched Connections


Selecting WAN

While connecting a LAN to a WAN, you should be aware of the connection requirements

Some of the major factors that help to select a WAN are: Frequency Transfer rates Traffic load Cost


Data-Link Protocols

Data-link layer protocols are commonly called the data link protocols

These protocols communicate between two devices such as, routers, and bridges

Data packets are sent over the link created by the protocols

Data-link protocols consist of: High Level Data Link Control (HDLC) protocol Point-to-Point protocol (PPP)


HDLC Frames


HDLC Frame Fields

Field Name Description

Flag Contains a single byte which indicates the beginning or end of a frame

Address Contains the broadcast address which is a binary sequence

Control Contains a single byte of binary sequence. This calls for transmission of user data in a non-sequence frame

Proprietary Contains information about the way to carry multiple protocols on a single link

Data Contains encapsulated data. The range if this field is variable

FCS Contains 2 to 4 bytes. Improves error detection


Types of HDLC Frames


Configuring HDLC

The encapsulation on a Cisco synchronous serial interface is HDLC

HDLC needs to be configured if the data link protocol is change to some other protocol, and HDLC has to be set back to default

To configure the HDLC protocol to be set as default, use the router CLI


Output of HDLC Verification


PPP

The PPP allows computers to connect to the Internet using a dial-up telephone line and ISDN

PPP was originally designed to transport IP traffic over point-to-point links

PPP can transfer data over synchronous and asynchronous links

It supports a transfer of data over different network protocols


PPP Frame

The frame format of PPP is similar to the HDLC Frame

The only difference is that, PPP includes a Protocol field

The PPP frame is made up of six fields as shown in Figure


PPP Stack


Link Control Protocol (LCP)

The PPP Link Control Protocol can establish, configure, maintain and terminate point-to-point connection between the devices

LCP uses following three classes of frames for establishing, configuring, maintaining and terminating connection between the devices: Link Configuration frames Link Maintenance frames Link Termination frames


Communication Between Devices


LCP Configuration Options

The LCP configuration options are: Authentication Compression Error-detection Multilink PPP callback


PPP Session Establishment

Point-to-Point protocol is used to transmit data packets over serial point-to-point links

The three phases of session establishment are given as follows: Link establishment phase Authentication phase Network layer protocol phase


PPP Authentication - I

Point-to-Point protocol supports authentication of devices

Once a link is established between nodes the process of authentication starts

PPP supports two authentication protocols Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP)


PPP Authentication - II


CHAP Authentication


Configuring PPP

Cisco allows you to configure the PPP to be used on WAN interface

You can configure the PPP using encapsulation and interface commands in the configuration mode

The syntax of the command to configure PPP is: encapsulation ppp


Configuring PPP Authentication Once the serial interface is configured to support the

PPP encapsulation, you must configure PPP authentication on the routers

Before authentication process, it is required to set a hostname for the router if not already assigned

Also, you must set username and password for the remote router to which the router is connected

After the hostname, username and password is set , select the appropriate authentication for the router such as PAP or CHAP


Verifying PPP Encapsulation

PPP does not begin authentication until the Link Control Protocol (LCP) process is completed and open

PPP authentication needs to be set up on both ends for the authentication process to work

Using commands, such as show and debug you can solve problems for PPP


Mismatched WAN Encapsulations Routers can communicate in a network only if their

encapsulation methods are same If you connect two routers in the network using

point-to-point link but the encapsulation methods are different on each router, the connection between the routers is not established

In this case, if one router sends request to the other, it will never receive a response from that router


Mismatched IP Addresses

Routers configured with same WAN encapsulation method such as PPP, HDLC or Frame Relay connected in different subnets will have connection established between them

However, the data packets do not transfer between the routers. It becomes very difficult to identify this problem, as the link appears to be functioning properly

To resolve the problem, you can use the show running-config and show interface command on each router


Case Study

The Blue Diamond steel company, Gujarat branch has all Cisco routers connected in the network. The router of the Business Development department is damaged. The computers in this department cannot exchange data with the other departments in the network. The network administrator Robert replaces the damaged router with a new non-Cisco router.


Problem

The Business Development department still cannot have transaction with the other departments


Suggested Solution

Cisco routers by default use HDLC as the serial encapsulation method on Cisco serial links. If you connect a non-Cisco router to a Cisco router in the network, data transfer does not occur between them. To enable communication between the routers, implement the Point-to-Point encapsulation method. You must configure PPP on all the serial interfaces of both the routers


Comparing HDLC and PPP - I

HDLC PPP

Fails to provide a method of detecting errors

Uses FCS to detect errors while transmitting data

Consist of two types; ISO HDLC and Cisco HDLC

Based on ISO's HDLC frame format

Supports synchronous and asynchronous links

Supports synchronous, asynchronous, High-Speed Serial Interface (HSSI), and ISDN links


Comparing HDLC and PPP - IIUsed to perform encapsulation of data without using other encapsulation protocols

Used to transfer data. PPP cannot encapsulate data without the help of other encapsulation protocols, such as, HDLC and Synchronous Data Link Control (SDLC)

Fails to provide authentication between two nodes or devices

Provides authentication using protocols, such as, PPP Authentication Protocol (PAP), and Challenge Handshake Authentication Protocol (CHAP)


Comparing HDLC and PPP - IIIProvides a frame format that contains a proprietary field. The other six fields are similar to the PPP frame field. Note, the ISO HDLC frame contains only six fields, as the proprietary field is not present

Provides a frame format that contains a protocol field. The other six fields are similar to the HDLC frame field

Fails to check for quality of a link established

Uses Link Control Protocol (LCP) to the check for quality of an established link


Summary - I

WAN is a network that spans a large geographical area

Leased lines are a transmission line, which is provided by telephone companies to a particular customer

Frequency, usage, traffic and cost are factors that need to considered when selecting a WAN connection

Data-Link layer protocols are commonly called the data link protocols, which communicate between two devices


Summary - II

Configuring HDLC only needs to be done only if the data link protocol is change to some other protocol

The two types of HDLC: ISO HDLC Cisco HDLC

The Cisco HDLC contains proprietary field, which defines carrying a multiple protocols across a link

PPP enables computers to connect to the internet using a dial-up telephone line and ISDN

Configuring the PPP is to specify that PPP is to be used on the WAN


Summary - III Features of PPP are:

Authentication Link test Error-detection Compression

Components of PPP are: HDLC LCP NCPs

Authentication protocols supported by PPP are: PAP CHAP


Summary - IV

By default the authentication is not mandatory but must be specified to

PAP is a insecure protocol because the username and password is sent in plain text

Using CHAP protocol the server sends challenge messages to the node. The node calculates and sends the results back to the server

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CCNA CHAPTER 9 BY jetarvind kumar madhukar

Education