CCNA 2 :- Module 1 Router and Routing Basic Overview

Overview
A wide-area network (WAN) is a data communications network that connects user networks over a large geographical area. WANs have several important characteristics that distinguish them from LANs. The first lesson in this module will provide an overview of WAN technologies and protocols. It will also explain how WANs and LANs are different, and ways in which they are similar.

 

It is important to understand the physical layer components of a router. This knowledge builds a foundation for other information and skills that are needed to configure routers and manage routed networks. This module provides a close examination of the internal and external physical components of the router. The module also describes techniques for physically connecting the various router interfaces.

 

This module covers some of the objectives for the CCNA 640-801, INTRO 640-821, and ICND 640-811 exams. -

Students who complete this module should be able to perform the following tasks:

• Identify organizations responsible for WAN standards  
• Explain the difference between a WAN and LAN and the type of standards and protocols each uses  
• Describe the role of a router in a WAN  
• Identify internal components of the router and describe their functions  
• Describe the physical characteristics of the router  
• Identify LAN and management ports on a router  
• Properly connect Ethernet, serial WAN, and console ports

 

Notice for all viewers :)

Notice

The first semester of CCNA has publised with 11 Chapter. Please send feed back on my email, if all reader of have any question, please must write back. I feel happy.

The second semester will update after few days, this is under process. Hope all will enjoy.

Aqeel Haider
(Writer)

Summary of Module 11

Summary
This page summarizes the topics discussed in this module.


The primary duties of the transport layer, Layer 4 of the OSI model, are to transport and regulate the flow of information from the source to the destination reliably and accurately.

The transport layer multiplexes data from upper layer applications into a stream of data packets. It uses port (socket) numbers to identify different conversations and delivers the data to the correct application.

The Transmission Control Protocol (TCP) is a connection-oriented transport protocol that provides flow control as well as reliability. TCP uses a three-way handshake to establish a synchronized circuit between end-user applications. Each datagram is numbered before transmission. At the receiving station, TCP reassembles the segments into a complete message. If a sequence number is missing in the series, that segment is retransmitted.

Flow control ensures that a transmitting node does not overwhelm a receiving node with data. The simplest method of flow control used by TCP involves a “not ready” signal that notifies the transmitting device that the buffers on the receiving device are full. When the receiver can handle additional data, the receiver sends a “ready” transport indicator.

Positive acknowledgment with retransmission is another TCP protocol technique that guarantees reliable delivery of data. Because having to wait for an acknowledgment after sending each packet would negatively impact throughput, windowing is used to allow multiple packets to be transmitted before an acknowledgment is received. TCP window sizes are variable during the lifetime of a connection.

Positive acknowledgment with retransmission is another TCP protocol technique that guarantees reliable delivery of data. Because having to wait for an acknowledgment after sending each packet would negatively impact throughput, windowing is used to allow multiple packets to be transmitted before an acknowledgment is received. TCP window sizes are variable during the lifetime of a connection.

If an application does not require flow control or an acknowledgment, as in the case of a broadcast transmission, User Datagram Protocol (UDP) can be used instead of TCP. UDP is a connectionless transport protocol in the TCP/IP protocol stack that allows multiple conversations to occur simultaneously but does not provide acknowledgments or guaranteed delivery. A UDP header is much smaller than a TCP header because of the lack of control information it must contain.

Some of the protocols and applications that function at the application level are well known to Internet users:

• Domain Name System (DNS) - Used in IP networks to translate names of network nodes into IP addresses

• File Transfer Protocol (FTP) - Used for transferring files between networks

• Hypertext Transfer Protocol (HTTP) - Used to deliver hypertext markup language (HTML) documents to a client application, such as a WWW browser

• Simple Mail Transfer Protocol (SMTP) - Used to provide electronic mail services

• Simple Network Management Protocol (SNMP) - Used to monitor and control network devices and to manage configurations, statistics collection, performance and security

• Telnet - Used to login to a remote host that is running a Telnet server application and then to execute commands from the command line

SMTP / SNMP / Telnet

SMTP
11.2.5 This page will discuss the features of SMTP.


Email servers communicate with each other using the Simple Mail Transfer Protocol (SMTP) to send and receive mail. The SMTP protocol transports email messages in ASCII format using TCP.

When a mail server receives a message destined for a local client, it stores that message and waits for the client to collect the mail. There are several ways for mail clients to collect their mail. They can use programs that access the mail server files directly or collect their mail using one of many network protocols. The most popular mail client protocols are POP3 and IMAP4, which both use TCP to transport data. Even though mail clients use these special protocols to collect mail, they almost always use SMTP to send mail. Since two different protocols, and possibly two different servers, are used to send and receive mail, it is possible that mail clients can perform one task and not the other. Therefore, it is usually a good idea to troubleshoot e-mail sending problems separately from e-mail receiving problems.

When checking the configuration of a mail client, verify that the SMTP and POP or IMAP settings are correctly configured. A good way to test if a mail server is reachable is to Telnet to the SMTP port (25) or to the POP3 port (110). The following command format is used at the Windows command line to test the ability to reach the SMTP service on the mail server at IP address 192.168.10.5:

C:\>telnet 192.168.10.5 25

The SMTP protocol does not offer much in the way of security and does not require any authentication. Administrators often do not allow hosts that are not part of their network to use their SMTP server to send or relay mail. This is to prevent unauthorized users from using their servers as mail relays.

The next page will describe the features of SNMP.

SNMP
11.2.6 This page will define SNMP.


The Simple Network Management Protocol (SNMP) is an application layer protocol that facilitates the exchange of management information between network devices. SNMP enables network administrators to manage network performance, find and solve network problems, and plan for network growth. SNMP uses UDP as its transport layer protocol.

An SNMP managed network consists of the following three key components:

• Network management system (NMS) – NMS executes applications that monitor and control managed devices. The bulk of the processing and memory resources required for network management are provided by NMS. One or more NMSs must exist on any managed network.

• Managed devices – Managed devices are network nodes that contain an SNMP agent and that reside on a managed network. Managed devices collect and store management information and make this information available to NMSs using SNMP. Managed devices, sometimes called network elements, can be routers, access servers, switches, and bridges, hubs, computer hosts, or printers.

• Agents – Agents are network-management software modules that reside in managed devices. An agent has local knowledge of management information and translates that information into a form compatible with SNMP.

The next page will describe Telnet.

Telnet
11.2.7 This page will explain the features of Telnet.


Telnet client software provides the ability to login to a remote Internet host that is running a Telnet server application and then to execute commands from the command line. A Telnet client is referred to as a local host. Telnet server, which uses special software called a daemon, is referred to as a remote host.

To make a connection from a Telnet client, the connection option must be selected. A dialog box typically prompts for a host name and terminal type. The host name is the IP address or DNS name of the remote computer. The terminal type describes the type of terminal emulation that the Telnet client should perform. The Telnet operation uses none of the processing power from the transmitting computer. Instead, it transmits the keystrokes to the remote host and sends the resulting screen output back to the local monitor. All processing and storage take place on the remote computer.

Telnet works at the application layer of the TCP/IP model. Therefore, Telnet works at the top three layers of the OSI model. The application layer deals with commands. The presentation layer handles formatting, usually ASCII. The session layer transmits. In the TCP/IP model, all of these functions are considered to be part of the application layer.

This page concludes this lesson. The next page will summarize the main points from the module.

FTP and TFTP / HTTP

FTP and TFTP
11.2.3 This page will describe the features of FTP and TFPT.


FTP is a reliable, connection-oriented service that uses TCP to transfer files between systems that support FTP. The main purpose of FTP is to transfer files from one computer to another by copying and moving files from servers to clients, and from clients to servers. When files are copied from a server, FTP first establishes a control connection between the client and the server. Then a second connection is established, which is a link between the computers through which the data is transferred. Data transfer can occur in ASCII mode or in binary mode. These modes determine the encoding used for data file, which in the OSI model is a presentation layer task. After the file transfer has ended, the data connection terminates automatically. When the entire session of copying and moving files is complete, the command link is closed when the user logs off and ends the session.

TFTP is a connectionless service that uses User Datagram Protocol (UDP). TFTP is used on the router to transfer configuration files and Cisco IOS images and to transfer files between systems that support TFTP. TFTP is designed to be small and easy to implement. Therefore, it lacks most of the features of FTP. TFTP can read or write files to or from a remote server but it cannot list directories and currently has no provisions for user authentication. It is useful in some LANs because it operates faster than FTP and in a stable environment it works reliably.

The next page will discuss HTTP.

HTTP
11.2.4 This page will describe the features of HTTP.


Hypertext Transfer Protocol (HTTP) works with the World Wide Web, which is the fastest growing and most used part of the Internet. One of the main reasons for the extraordinary growth of the Web is the ease with which it allows access to information. A Web browser is a client-server application, which means that it requires both a client and a server component in order to function. A Web browser presents data in multimedia formats on Web pages that use text, graphics, sound, and video. The Web pages are created with a format language called Hypertext Markup Language (HTML). HTML directs a Web browser on a particular Web page to produce the appearance of the page in a specific manner. In addition, HTML specifies locations for the placement of text, files, and objects that are to be transferred from the Web server to the Web browser.

Hyperlinks make the World Wide Web easy to navigate. A hyperlink is an object, word, phrase, or picture, on a Web page. When that hyperlink is clicked, it directs the browser to a new Web page. The Web page contains, often hidden within its HTML description, an address location known as a Uniform Resource Locator (URL).

In the URL http://www.cisco.com/edu/, the "http://" tells the browser which protocol to use. The second part, "www", is the hostname or name of a specific machine with a specific IP address. The last part, /edu/ identifies the specific folder location on the server that contains the default web page.

A Web browser usually opens to a starting or "home" page. The URL of the home page has already been stored in the configuration area of the Web browser and can be changed at any time. From the starting page, click on one of the Web page hyperlinks, or type a URL in the address bar of the browser. The Web browser examines the protocol to determine if it needs to open another program, and then determines the IP address of the Web server using DNS. Then the transport layer, network layer, data link layer, and physical layer work together to initiate a session with the Web server. The data that is transferred to the HTTP server contains the folder name of the Web page location. The data can also contain a specific file name for an HTML page. If no name is given, then the default name as specified in the configuration on the server is used.

The server responds to the request by sending to the Web client all of the text, audio, video, and graphic files specified in the HTML instructions. The client browser reassembles all the files to create a view of the Web page, and then terminates the session. If another page that is located on the same or a different server is clicked, the whole process begins again.

The next page will describe the protocol used to send e-mail.

Introduction to the TCP/IP application layer / DNS

Introduction to the TCP/IP application layer
11.2.1 This page will introduce some TCP/IP application layer protocols.


The session, presentation, and application layers of the OSI model are bundled into the application layer of the TCP/IP model. This means that representation, encoding, and dialog control are all handled in the TCP/IP application layer. This design ensures that the TCP/IP model provides maximum flexibility at the application layer for software developers.

The TCP/IP protocols that support file transfer, e-mail, and remote login are probably the most familiar to users of the Internet. These protocols include the following applications:

• DNS
• FTP
• HTTP
• SMTP
• SNMP
• Telnet

The next page will discuss DNS.

DNS
11.2.2 This page will describe DNS.


The Internet is built on a hierarchical addressing scheme. This scheme allows for routing to be based on classes of addresses rather than based on individual addresses. The problem this creates for the user is associating the correct address with the Internet site. It is very easy to forget an IP address to a particular site because there is nothing to associate the contents of the site with the address. Imagine the difficulty of remembering the IP addresses of tens, hundreds, or even thousands of Internet sites.

A domain naming system was developed in order to associate the contents of the site with the address of that site. The Domain Name System (DNS) is a system used on the Internet for translating names of domains and their publicly advertised network nodes into IP addresses. A domain is a group of computers that are associated by their geographical location or their business type. A domain name is a string of characters, number, or both. Usually a name or abbreviation that represents the numeric address of an Internet site will make up the domain name. There are more than 200 top-level domains on the Internet, examples of which include the following:

.us – United States
.uk – United Kingdom

There are also generic names, which examples include the following:

.edu – educational sites
.com – commercial sites
.gov – government sites
.org – non-profit sites
.net – network service

The next page will discuss FTP and TFTP.

UDP

UDP
11.1.8 This page will discuss UDP. UDP is the connectionless transport protocol in the TCP/IP protocol stack.


UDP is a simple protocol that exchanges datagrams without guaranteed delivery. It relies on higher-layer protocols to handle errors and retransmit data.

UDP does not use windows or ACKs. Reliability is provided by application layer protocols. UDP is designed for applications that do not need to put sequences of segments together.

The following protocols use UDP:

• TFTP
• SNMP
• DHCP
• DNS

The following are the definitions of the fields in the UDP segment:

• Source port – Number of the port that sends data
• Destination port – Number of the port that receives data
• Length – Number of bytes in header and data
• Checksum – Calculated checksum of the header and data fields
• Data – Upper-layer protocol data

The next page discusses port numbers used by both TCP and UDP.

TCP and UDP port numbers
11.1.9 This page examines port numbers.


Both TCP and UDP use port numbers to pass information to the upper layers. Port numbers are used to keep track of different conversations that cross the network at the same time.

Application software developers agree to use well-known port numbers that are issued by the Internet Assigned Numbers Authority (IANA). Any conversation bound for the FTP application uses the standard port numbers 20 and 21. Port 20 is used for the data portion and Port 21 is used for control. Conversations that do not involve an application with a well-known port number are assigned port numbers randomly from within a specific range above 1023. Some ports are reserved in both TCP and UDP. However, applications might not be written to support them. Port numbers have the following assigned ranges:

• Numbers below 1024 are considered well-known ports numbers.
• Numbers above 1024 are dynamically-assigned ports numbers.
• Registered port numbers are for vendor-specific applications. Most of these are above 1024.

End systems use port numbers to select the proper application. The source host dynamically assigns source port numbers. These numbers are always greater than 1023.

This page concludes this lesson. The next lesson will focus on the application layer. The first page provides an introduction.