W&L Page 1 CCNA 200-120 CCNA 200-120 Training Jose Luis Flores / Amel Walkinshaw Aug, 2015.

W&L Page 1CCNA 200-120

CCNA 200-120 Training

Jose Luis Flores / Amel Walkinshaw

Aug, 2015


1.0 Operation of IP Data Networks

1.1 Recognize the purpose and functions of various network devices such as routers, switches, bridges and hubs 1.2 Select the components required to meet a given network specification 1.3 Identify common applications and their impact on the network 1.4 Describe the purpose and basic operation of the protocols in the OSI and TCP/IP models 1.5 Predict the data flow between two hosts across a network 1.6 Identify the appropriate media, cables, ports, and connectors to connect Cisco network devices to other network devices and hosts in a LAN


1.3 Identify common applications and their impact on the network

All communication, whether face-to-face or over a network, is governed by predetermined rules called protocols. These protocols are specific to the characteristics of the conversation. In our day-to-day personal communication, the rules we use to communicate over one medium, like a telephone call, are not necessarily the same as the protocols for using another medium, such as sending a letter. Think of how many different rules or protocols govern all the different methods of communication that exist in the world today. Successful communication between hosts on a network requires the interaction of many different protocols.

A group of inter-related protocols that are necessary to perform a communication function is called a protocol suite. These protocols are implemented in software and hardware that is loaded on each host and network device. One of the best ways to visualize how all of the protocols interact on a particular host is to view it as a stack. A protocol stack shows how the individual protocols within the suite are implemented on the host. The protocols are viewed as a layered hierarchy, with each higher level service depending on the functionality defined by the protocols shown in the lower levels. The lower layers of the stack are concerned with moving data over the network and providing services to the upper layers, which are focused on the content of the message being sent and the user interface.


Using layers to describe face-to-face communication

For example, consider two people communicating face-to-face. At the bottom layer, the physical layer, we have two people, each with a voice that can utter words aloud. At the second layer, the rules layer, we have an agreement to speak in a common language. At the top layer, the content layer, we have the words actually spoken-the content of the communication. Were we to witness this conversation, we would not actually see "layers" floating in space. It is important to understand that the use of layers is a model and, as such, it provides a way to conveniently break a complex task into parts and describe how they work.



Network Protocols

At the human level, some communication rules are formal and others are simply understood, or implicit, based on custom and practice. For devices to successfully communicate, a network protocol suite must describe precise requirements and interactions.

Networking protocol suites describe processes such as:

•The format or structure of the message•The method by which networking devices share information about pathways with other networks •How and when error and system messages are passed between devices •The setup and termination of data transfer sessions

Individual protocols in a protocol suite may be vendor-specific and proprietary. Proprietary, in this context, means that one company or vendor controls the definition of the protocol and how it functions. Some proprietary protocols can be used by different organizations with permission from the owner. Others can only be implemented on equipment manufactured by the proprietary vendor.



Protocol Suites and Industry StandardsOften, many of the protocols that comprise a protocol suite reference other widely utilized protocols or industry standards. A standard is a process or protocol that has been endorsed by the networking industry and ratified by a standards organization, such as the Institute of Electrical and Electronics Engineers (IEEE) or the Internet Engineering Task Force (IETF). The use of standards in developing and implementing protocols ensures that products from different manufacturers can work together for efficient communications. If a protocol is not rigidly observed by a particular manufacturer, their equipment or software may not be able to successfully communicate with products made by other manufacturers. In data communications, for example, if one end of a conversation is using a protocol to govern one-way communication and the other end is assuming a protocol describing two-way communication, in all probability, no information will be exchanged

The Interaction of ProtocolsAn example of the use of a protocol suite in network communications is the interaction between a web server and a web browser. This interaction uses a number of protocols and standards in the process of exchanging information between them. The different protocols work together to ensure that the messages are received and understood by both parties. Examples of these protocols are:



Application Protocol:Hypertext Transfer Protocol (HTTP) is a common protocol that governs the way that a web server and a web client interact. HTTP defines the content and formatting of the requests and responses exchanged between the client and server. Both the client and the web server software implement HTTP as part of the application. The HTTP protocol relies on other protocols to govern how the messages are transported between client and server.

Transport Protocol: Transmission Control Protocol (TCP) is the transport protocol that manages the individual conversations between web servers and web clients. TCP divides the HTTP messages into smaller pieces, called segments, to be sent to the destination client. It is also responsible for controlling the size and rate at which messages are exchanged between the server and the client.

Internetwork Protocol: The most common internetwork protocol is Internet Protocol (IP). IP is responsible for taking the formatted segments from TCP, encapsulating them into packets, assigning the appropriate addresses, and selecting the best path to the destination host.



Network Access Protocols:Network access protocols describe two primary functions, data link management and the physical transmission of data on the media. Data-link management protocols take the packets from IP and format them to be transmitted over the media. The standards and protocols for the physical media govern how the signals are sent over the media and how they are interpreted by the receiving clients. Transceivers on the network interface cards implement the appropriate standards for the media that is being used.



Technology Independent Protocols

Networking protocols describe the functions that occur during network communications. In the face-to-face conversation example, a protocol for communicating might state that in order to signal that the conversation is complete, the sender must remain silent for two full seconds. However, this protocol does not specify how the sender is to remain silent for the two seconds. Protocols generally do not describe how to accomplish a particular function. By describing only what functions are required of a particular communication rule but not how they are to be carried out, the implementation of a particular protocol can be technology-independent.

Looking at the web server example, HTTP does not specify what programming language is used to create the browser, which web server software should be used to serve the web pages, what operating system the software runs on, or the hardware requirements necessary to display the browser. It also does not describe how the server should detect errors, although it does describe what the server should do if an error occurs. This means that a computer - and other devices, like mobile phones or PDAs - can access a web page stored on any type of web server that uses any form of operating system from anywhere on the Internet.



We´ll go over the the different applications and services typically used in IP networks, and although there are many more protocols defined here, we´ll focus on the protocols most relevants to the CCNA objectives.

Here’s a list of the protocols and applications we´ll cover in this section:

• Telnet• SSH• FTP• TFTP• SNMP• HTTP• HTTPS• NTP• DNS• DHCP / BootP



Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. Through Telnet, an administrator or another user can access someone else's computer remotely.

Stands for "Secure Shell." SSH is a method of securely communicating with another computer. The "secure" part of the name means that all data sent via an SSH connection is encrypted. This means if a third party tries to intercept the information being transferred, it would appear scrambled and unreadable. The "shell" part of the name means SSH is based on a Unix shell, which is a program that interprets commands entered by a user.



Stands for "File Transfer Protocol." FTP is a protocol designed for transferring files over the Internet. Files stored on an FTP server can be accessed using an FTP client, such as a web browser, FTP software program, or a command line interface.

An FTP server can be configured to enable different types of access. For example, an "anonymous FTP" configuration allows anyone to connect to the server. However, anonymous users may only be allowed to view certain directories and may not be able to upload files. If anonymous FTP access is disabled, users are required to log in in order to view and download files.

The standard FTP protocol is not encrypted, meaning it is vulnerable to packet sniffers and other types of snooping attacks. Therefore, the FTPS and SFTP protocols were developed to provide secure FTP connections. FTPS (FTP with SSL security) provides SSL encryption for all FTP communication. SFTP (SSH File Transfer Protocol) is a secure version of FTP that uses SSH to encrypt all data transfers.



Stands for "Trivial File Transfer Protocol." TFTP is a file transfer protocol similar to FTP, but is much more limited. Unlike FTP, TFTP does not support authentication and cannot change directories or list directory contents. Therefore, it is most often used to transfer individual files over a local network. TFTP may also be used to boot a computer system from a network-connected storage device.

While FTP connections use the TCP protocol, TFTP connections are made over UDP, which requires less overhead than TCP. This means TFTP file transfers may be faster, but less reliable than FTP transfers. Port 20 is used for FTP transfers, while port 69 is used for transferring files via TFTP.



Stands for "Simple Network Management Protocol." SNMP is used for exchanging management information between network devices. For example, SNMP may be used to configure a router or simply check its status. There are four types of SNMP commands used to control and monitor managed devices: 1) read, 2) write, 3) trap, and 4) traversal operations.

The read command is used to monitor devices, while the write command is used to configure devices and change device settings. The trap command is used to "trap" events from the device and report them back to the monitoring system. Traversal operations are used to determine what variables a certain device supports.

SNMP has no authentication capabilities, which means it is not a very secure protocol. For this reason, SNMP is often used for monitoring networks rather than managing them. So, practically speaking, SNMP could be considered as a "Simple Network Monitoring Protocol" instead.



Stands for "Hypertext Transfer Protocol." HTTP is the protocol used to transfer data over the web. It is part of the Internet protocol suite and defines commands and services used for transmitting webpage data.

HTTP uses a server-client model. A client, for example, may be a home computer, laptop, or mobile device. The HTTP server is typically a web host running web server software, such as Apache or IIS. When you access a website, your browser sends a request to the corresponding web server and it responds with an HTTP status code. If the URL is valid and the connection is granted, the server will send your browser the webpage and related files.

Some common HTTP status codes include:

200 - successful request (the webpage exists) 301 - moved permanently (often forwarded to a new URL) 401 - unauthorized request (authorization required) 403 - forbidden (access is not allowed to the page or directory) 500 - internal server error (often caused by an incorrect server configuration)

HTTP also defines commands such as GET and POST, which are used to handle form submissions on websites. The CONNECT command is used to facilitate a secure connection that is encrypted using SSL. Encrypted HTTP connections take place over HTTPS, an extension of HTTP designed for secure data transmissions.



Stands for "HyperText Transport Protocol Secure." HTTPS is the same thing as HTTP, but uses a secure socket layer (SSL) for security purposes. Some examples of sites that use HTTPS include banking and investment websites, e-commerce websites, and most websites that require you to log in.

Websites that use the standard HTTP protocol transmit and receive data in an unsecured manner. This means it is possible for someone to eavesdrop on the data being transferred between the user and the Web server. While this is highly unlikely, it is not a comforting thought that someone might be capturing your credit card number or other personal information that you enter on a website. Therefore, secure websites use the HTTPS protocol to encrypt the data being sent back and forth with SSL encryption. If someone were to capture the data being transferred via HTTPS, it would be unrecognizable.



Network Time Protocol (NTP) is a protocol that is used to synchronize computer clock times in a network of computers.

NTP uses Coordinated Universal Time (UTC) to synchronize computer clock times to a millisecond, and sometimes to a fraction of a millisecond. UTC time is obtained using several different methods, including radio and satellite systems. Specialized receivers are available for high-level services such as the Global Positioning System (GPS) and the governments of some nations. However, it is not practical or cost-effective to equip every computer with one of these receivers. Instead, computers designated as primary time servers are outfitted with the receivers and they use protocols such as NTP to synchronize the clock times of networked computers. Degrees of separation from the UTC source are defined as strata. A radio clock (which receives true time from a dedicated transmitter or satellite navigation system) is stratum-0; a computer that is directly linked to the radio clock is stratum-1; a computer that receives its time from a stratum-1 computer is stratum-2, and so on.

Accurate time across a network is important for many reasons; even small fractions of a second can cause problems. For example, distributed procedures depend on coordinated times to ensure that proper sequences are followed. Security mechanisms depend on coordinated times across the network. File system updates carried out by a number of computers also depend on synchronized clock times. Air traffic control systems provide a graphic illustration of the need for coordinated times, since flight paths require very precise timing (imagine the situation if air traffic controller computer clock times were not synchronized).



The term NTP applies to both the protocol and the client/server programs that run on computers. The programs are compiled by the user as an NTP client, NTP server, or both. In basic terms, the NTP client initiates a time request exchange with the time server. As a result of this exchange, the client is able to calculate the link delay and its local offset, and adjust its local clock to match the clock at the server's computer. As a rule, six exchanges over a period of about five to 10 minutes are required to initially set the clock. Once synchronized, the client updates the clock about once every 10 minutes, usually requiring only a single message exchange. In addition to client/server synchronization, NTP also supports broadcast synchronization of peer computer clocks. Unfortunately, the NTP protocol can be exploited and used for denial of service (DoS) attacks because it will reply to a packet with a spoofed source IP address and because at least one of its built-in commands will send a long reply to a short request.

NTP, which was developed by David Mills at the University of Delaware, is designed to be highly fault-tolerant and scalable.



Stands for "Domain Name System." Domain names serve as memorizable names for websites and other services on the Internet. However, computers access Internet devices by their IP addresses. DNS translates domain names into IP addresses, allowing you to access an Internet location by its domain name.

Thanks to DNS, you can visit a website by typing in the domain name rather than the IP address. For example, to visit the Tech Terms Computer Dictionary, you can simply type "techterms.com" in the address bar of your web browser rather than the IP address (67.43.14.98). It also simplifies email addresses, since DNS translates the domain name (following the "@" symbol) to the appropriate IP address.

To understand how DNS works, you can think of it like the contacts app on your smartphone. When you call a friend, you simply select his or her name from a list. The phone does not actually call the person by name, it calls the person's phone number. DNS works the same way by associating a unique IP address with each domain name.



Unlike your address book, the DNS translation table is not stored in a single location. Instead, the data is stored on millions of servers around the world. When a domain name is registered, it must be assigned at least two nameservers (which can be edited through the domain name registrar at any time). The nameserver addresses point to a server that has a directory of domain names and their associated IP addresses. When a computer accesses a website over the Internet, it locates the corresponding nameserver and gets the correct IP address for the website.

Since DNS translation creates additional overhead when connecting to websites, ISPs cache DNS records and host the data locally. Once the IP address of a domain name is cached, an ISP can automatically direct subsequent requests to the appropriate IP address. This works great until an IP address changes, in which case the request may be sent to the wrong server or the server will not respond at all. Therefore, DNS caches are updated regularly, usually somewhere between a few hours and a few days.



Stands for "Dynamic Host Configuration Protocol." DHCP is a protocol that automatically assigns a unique IP address to each device that connects to a network. With DHCP, there is no need to manually assign IP addresses to new devices. Therefore, no user configuration is necessary to connect to a DCHP-based network. Because of its ease of use and widespread support, DHCP is the default protocol used by most routers and networking equipment.

When you connect to a network, your device is considered a client and the router is the server. In order to successfully connect to a network via DHCP, the following steps must take place.

• When a client detects it has connected to a DHCP server, it sends a DHCPDISCOVER request.• The router either receives the request or redirects it to the appropriate DHCP server.• If the server accepts the new device, it will send a DHCPOFFER message back to the client, which contains the

client device's MAC address and the IP address being offered.• The client returns a DHCPREQUEST message to the server, confirming it will use the IP address.• Finally, the server responds with a DHCPACK acknowledgement message that confirms the client has been given

access (or a "lease") for a certain amount of time.



DHCP works in the background when you connect to a network, so you will rarely see any of the above steps happen. The time it takes to connect via DHCP depends on the type of router and the size of the network, but it usually takes around three to ten seconds. DHCP works the same way for both wired and wireless connections, which means desktop computers, tablets, and smartphones can all connect to a DHCP-based network at the same time.

BOOTP (Bootstrap Protocol) definition

BOOTP (Bootstrap Protocol) is a protocol that lets a network user be automatically configured (receive an IP address) and have an operating system booted (initiated) without user involvement. The BOOTP server, managed by a network administrator, automatically assigns the IP address from a pool of addresses for a certain duration of time.BOOTP is the basis for a more advanced network manager protocol, the Dynamic Host Configuration Protocol (DHCP).



Exam Essentials

Identify process / applications layer protocols:

Telnet is a terminal emulation programthat allows you to login into a remote host and run programs. File Transfer Protocol (FTP) is a connection-oriented service that allows you to transfer files.TFTP (Trivial FTP) is a connectionless file transfer program.SMTP (Simple Mail Transfer Protocol) is a send mail program.

Describe the functions of DNS and DHCP in the network:

Dynamic Host Configuration Protocol (DHCP) provides network configuration information (including IP address) to hosts, eliminating the need to perform the configuration manually.Domain Name Service (DNS) resolves hostnames – both, internet and devices names – to IP address, eliminating the need to know the IP address of a device for connection purposes.



Bibliography

• http://www.cisco.com/c/en/us/td/docs/net_mgmt/subscriber_edge_services_manager/3-1-9/deployment/guide/deply/1intro.html• http://www.highteck.net/EN/Basic/Internetworking.html• http://searchnetworking.techtarget.com/definition/Telnet• http://techterms.com/definition/ssh• Christensson, P. (2007, October 11). SNMP Definition. Retrieved 2015, Aug 3, from http://techterms.com

http://www.cisco.com/c/en/us/td/docs/net_mgmt/subscriber_edge_services_manager/3-1-9/deployment/guide/deply/1intro.html

http://www.cisco.com/c/en/us/td/docs/net_mgmt/subscriber_edge_services_manager/3-1-9/deployment/guide/deply/1intro.html

http://www.highteck.net/EN/Basic/Internetworking.html

http://www.highteck.net/EN/Basic/Internetworking.html

http://searchnetworking.techtarget.com/definition/Telnet

http://searchnetworking.techtarget.com/definition/Telnet

http://techterms.com/definition/ssh

http://techterms.com/definition/ssh


Q&A

W&L Page 1 CCNA 200-120 CCNA 200-120 Training Jose Luis Flores / Amel Walkinshaw Aug, 2015.

Documents

network protocols

different protocols

individual protocols

communication rules

facetoface communication

rules layer

network protocol suite

cisco network devices