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NETWORK BASICS

Network A system of interconnected computers and computerized peripherals such as printers is called computer network. This interconnection among computers facilitates information sharing among them. Computers may connect to each other by either wired or wireless media. A computer network consists of a collection of computers, printers and other equipment that is connected together so that they can communicate with each other.  


Network application
A Network application is any application running on one host and provides a communication to another application running on a different host, the application may use an existing application layer protocols such as: HTTP(e.g. the Browser and web server), SMTP(e.g. the email-client). And may be the application does not use any existing protocols and depends on the socket programming to communicate to another application. So the web application is a type of the network applications. 
There are lots of advantages from build up a network, but the th…

NETWORK TROUBLESHOOTING TOOLS & STEPS

NETWORK TROUBLESHOOTING TOOLS & STEPSNetwork troubleshooting tools are a necessity for every network administrator. When getting started in the networking field, it is important to amass a number of tools that can be used to troubleshoot a variety of different network conditions. While it is true that the use of specific tools can be subjective and at the discretion of the engineer.



Ping 

The most commonly used network tool is the ping utility. This utility is used to provide a basic connectivity test between the requesting host and a destination host. This is done by using the Internet Control Message Protocol (ICMP) which has the ability to send an echo packet to a destination host and a mechanism to listen for a response from this host. Simply stated, if the requesting host receives a response from the destination host, this host is reachable. This utility is commonly used to provide a basic picture of where a specific networking problem may exist. For example, if an Internet connection is down at an office, the ping utility can be used to figure out whether the problem exists within the office or within the network of the Internet provider.

 Tracert/traceroute 

Typically, once the ping utility has been used to determine basic connectivity, the tracert/traceroute utility can used to determine more specific information about the path to the destination host including the route the packet takes and the response time of these intermediate hosts. Figure 2 below shows an example of the tracert utility being used to find the path from a host inside an office to www.google.com. The tracert utility and traceroute utilities perform the same function but operate on different operating systems, Tracert for Windows machines and traceroute for Linux/*nix based machines.

Ipconfig/ifconfig 

One of the most important things that must be completed when troubleshooting a networking issue is to find out the specific IP configuration of the variously affected hosts. Sometimes this information is already known when addressing is configured statically, but when a dynamic addressing method is used, the IP address of each host can potentially change often. The utilities that can be used to find out this IP configuration information include the ipconfig utility on Windows machines and the ifconfig utility on Linux/Unix based machines.

Nslookup

Some of the most common networking issues revolve around issues with Dynamic Name System (DNS) address resolution issues. DNS is used by everyone using the Internet to resolve commonly known domain names (i.e. google.com) to commonly unknown IP addresses (i.e. 74.125.115.147). When this system does not work, most of the functionality that people are used to goes away, as there is no way to resolve this information. The nslookup utility can be used to lookup the specific IP address (es) associated with a domain name. If this utility is unable to resolve this information, there is a DNS issue. Along with simple lookup, the nslookup utility is able to query specific DNS servers to determine an issue with the default DNS servers configured on a host.

Netstat 

Often, one of the things that are required to be figured out is the current state of the active network connections on a host. This is very important information to find for a variety of reasons. For example, when verifying the status of a listening port on a host or to check and see what remote hosts are connected to a local host on a specific port. It is also possible to use the netstat utility to determine which services on a host that is associated with specific active ports.

Speedtest.net/pingtest.net 

A very easy test that can be used to both determine the Internet bandwidth available to a specific host and to determine the quality of an Internet connection is the use of the tools available at the speedtest.net and pingtest.net websites.

The speedtest.net site provides the ability to determine the amount of bandwidth that is available to a specific host at a specific point in time; this is often a good tool to use when measuring how long it is going to take to upload or download information from a local to remote host. This measurement can also be used to determine whether the connection is offering the amount of bandwidth that was purchased from the Internet provider; keep in mind however that some amount of bandwidth difference is expected between the quoted bandwidth purchased and the measured bandwidth. The pingtest.net website is used to determine the quality of the connection by measuring the ping response times and jitter amounts over a short period of time. This information can be used to determine a likelihood of how well the measured connection will deal with certain types of high demand traffic like Voice over IP (VoIP) or gaming.

Pathping/mtr 

In an effort to take advantage of the benefits of both the ping and tracert/traceroute commands, the pathping and mtr utilities were developed. Both of these tools take the functionality and information that can be obtained from these types of tools and provide a more detailed single picture of the path characteristics from a specific host to a specific destination.

Flush Your DNS Cache 

Whenever you type a URL into a Web browser, your PC asks your domain name service server (DNS server) to translate that URL into an IP address, and caches that information. That cache can occasionally become outdated or corrupt, which can cause Internet connection problems. To clear your DNS cache, open the Command Prompt with Run as Administrator, type ipconfig /flushdns, and press Enter.

Network troubleshooting steps in windows 7 

Windows 7 is designed for networking and working with the Internet, so when your network connection isn’t working, it can be particularly frustrating. Fortunately, Windows 7 comes with a built-in troubleshooter that you can use to repair a broken network connection.

Step 1: 

Choose Start→Control Panel→Network and Internet. Then click the Network and Sharing Center link.

Click the Fix a Network Problem link.

The link pulls you straight into the Control Panel’s Troubleshooting guide for the network.

Step 2:

Click the link for the type of network connection that has been lost.

There are several different troubleshooters available:

o Internet Connections: When you can’t connect to the Internet or to a particular Web site
o Connection to a Shared Folder: When you can’t connect to a file or folder that you thought was shared
o Home Group: When you’re unable to view files or computers in your home group
o Network Adapter: When you’re unable to communicate with your router or modem
o Incoming Connections to This Computer: When you’re unable to let other computers in your network communicate with your PC

Work your way through the troubleshooting guide. Windows 7 will ask you a series of questions. As you respond, you’ll get closer and closer to the answer. If Windows suggests an action you must perform, such as plugging in a cable, do so.

Step 3: 

When the solution is found, close the Network troubleshooting guide.

Sometimes the troubleshooter isn't able to correct the problem. In that case, it’s best to delete the connection and just create it again by clicking the Setup a New Connection or Network link in the Network and Sharing Center window and entering the correct settings.

Review Questions 

A user cannot access the local intranet. Which action will not help you determine how to narrow the problem down to the intranet? 

a. Accessing the intranet from your workstation
b. Accessing the intranet from the user’s workstation as yourself
c. Replacing the patch cable on the workstation
d. Asking another user to access the intranet from the problem user’s workstation

A user can’t log in to the network. She can’t even connect to the Internet over the LAN. Other users in the same area aren’t experiencing any problems. You attempt to log in as this user from your workstation with her username and password and don’t experience any problems. However, you cannot log in with either her username or yours from her workstation. What is a likely cause of the problem? 

a. Insufficient rights to access the server
b. A bad patch cable
c. Server down
d. Wrong username and password

A user calls you, reporting a problem logging in to the corporate intranet. You can access the website without problems using the user’s username and password. At your request, the user has tried logging in from other workstations but has been unsuccessful. What is the most likely cause of the problem? 

a. The user is logging in incorrectly.
b. The network is down.
c. The intranet server is locked up.
d. The server is not routing packets correctly to that user’s workstation.

You have gathered information on a network issue and determined the affected areas of the network. What is your next step in resolving this issue? 

a. You should implement what the best solution for the issue is
b. You should test the best solution for the issue
c. You should check to see if there have been any recent changes to this affected part of the network. d. You should consider any negative impact to the network that might be caused by a  Solution.

You are troubleshooting a LAN switch and have identified the symptoms. What is the next step you should take? 

a. Escalate the issue
b. Create an action plan
c. Implement the solution
d. Determine the scope of the problem 

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