Computer network

Definition

A computer network is a group of computers that use a set of common communication protocols over digital interconnections for the purpose of sharing resources located on or provided by the network nodes.

A network consists of two or more computers that are linked in order to share resources (such as printers and CDs), exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams. … Local Area Network (LAN)

Computer Network Types

A computer network is a group of computers linked to each other that enables the computer to communicate with another computer and share their resources, data, and applications.

A computer network can be categorized by their size. A computer network is mainly of four types:

• LAN(Local Area Network)
• PAN(Personal Area Network)
• MAN(Metropolitan Area Network)
• WAN(Wide Area Network)

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LAN(Local Area Network)

• Local Area Network is a group of computers connected to each other in a small area such as building, office.
• LAN is used for connecting two or more personal computers through a communication medium such as twisted pair, coaxial cable, etc.
• It is less costly as it is built with inexpensive hardware such as hubs, network adapters, and ethernet cables.
• The data is transferred at an extremely faster rate in Local Area Network.
• Local Area Network provides higher security.

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PAN(Personal Area Network)https://9dee2b3c5c21db422e2e913c268dd11c.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.html

• Personal Area Network is a network arranged within an individual person, typically within a range of 10 meters.
• Personal Area Network is used for connecting the computer devices of personal use is known as Personal Area Network.
• Thomas Zimmerman was the first research scientist to bring the idea of the Personal Area Network.
• Personal Area Network covers an area of 30 feet.
• Personal computer devices that are used to develop the personal area network are the laptop, mobile phones, media player and play stations.

There are two types of Personal Area Network:https://9dee2b3c5c21db422e2e913c268dd11c.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.htmlhttps://imasdk.googleapis.com/js/core/bridge3.453.0_en.html#goog_6075664

• Wired Personal Area Network
• Wireless Personal Area Network

Wireless Personal Area Network: Wireless Personal Area Network is developed by simply using wireless technologies such as WiFi, Bluetooth. It is a low range network.

Wired Personal Area Network: Wired Personal Area Network is created by using the USB.

Examples Of Personal Area Network:

• Body Area Network: Body Area Network is a network that moves with a person. For example, a mobile network moves with a person. Suppose a person establishes a network connection and then creates a connection with another device to share the information.
• Offline Network: An offline network can be created inside the home, so it is also known as a home network. A home network is designed to integrate the devices such as printers, computer, television but they are not connected to the internet.
• Small Home Office: It is used to connect a variety of devices to the internet and to a corporate network using a VPN

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MAN(Metropolitan Area Network)

• A metropolitan area network is a network that covers a larger geographic area by interconnecting a different LAN to form a larger network.
• Government agencies use MAN to connect to the citizens and private industries.
• In MAN, various LANs are connected to each other through a telephone exchange line.
• The most widely used protocols in MAN are RS-232, Frame Relay, ATM, ISDN, OC-3, ADSL, etc.
• It has a higher range than Local Area Network(LAN).

Uses Of Metropolitan Area Network:

• MAN is used in communication between the banks in a city.
• It can be used in an Airline Reservation.
• It can be used in a college within a city.
• It can also be used for communication in the military.

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WAN(Wide Area Network)

• A Wide Area Network is a network that extends over a large geographical area such as states or countries.
• A Wide Area Network is quite bigger network than the LAN.
• A Wide Area Network is not limited to a single location, but it spans over a large geographical area through a telephone line, fibre optic cable or satellite links.
• The internet is one of the biggest WAN in the world.
• A Wide Area Network is widely used in the field of Business, government, and education.

Examples Of Wide Area Network:

• Mobile Broadband: A 4G network is widely used across a region or country.
• Last mile: A telecom company is used to provide the internet services to the customers in hundreds of cities by connecting their home with fiber.
• Private network: A bank provides a private network that connects the 44 offices. This network is made by using the telephone leased line provided by the telecom company.

Advantages Of Wide Area Network:

Following are the advantages of the Wide Area Network:

• Geographical area: A Wide Area Network provides a large geographical area. Suppose if the branch of our office is in a different city then we can connect with them through WAN. The internet provides a leased line through which we can connect with another branch.
• Centralized data: In case of WAN network, data is centralized. Therefore, we do not need to buy the emails, files or back up servers.
• Get updated files: Software companies work on the live server. Therefore, the programmers get the updated files within seconds.
• Exchange messages: In a WAN network, messages are transmitted fast. The web application like Facebook, Whatsapp, Skype allows you to communicate with friends.
• Sharing of software and resources: In WAN network, we can share the software and other resources like a hard drive, RAM.
• Global business: We can do the business over the internet globally.
• High bandwidth: If we use the leased lines for our company then this gives the high bandwidth. The high bandwidth increases the data transfer rate which in turn increases the productivity of our company.

Disadvantages of Wide Area Network:

The following are the disadvantages of the Wide Area Network:

• Security issue: A WAN network has more security issues as compared to LAN and MAN network as all the technologies are combined together that creates the security problem.
• Needs Firewall & antivirus software: The data is transferred on the internet which can be changed or hacked by the hackers, so the firewall needs to be used. Some people can inject the virus in our system so antivirus is needed to protect from such a virus.
• High Setup cost: An installation cost of the WAN network is high as it involves the purchasing of routers, switches.
• Troubleshooting problems: It covers a large area so fixing the problem is difficult.

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Internetwork

• An internetwork is defined as two or more computer network LANs or WAN or computer network segments are connected using devices, and they are configured by a local addressing scheme. This process is known as internetworking.
• An interconnection between public, private, commercial, industrial, or government computer networks can also be defined as internetworking.
• An internetworking uses the internet protocol.
• The reference model used for internetworking is Open System Interconnection(OSI).

What is Network Troubleshooting?

Feb 15, 2019

Network troubleshooting is the combined measures and processes used to identify, diagnose and solve problems within a computer network. It’s a logical process that network engineers use to resolve network problems and improve network operations. Troubleshooting is an iterative process, the more data you collect and analyze, the higher the likelihood of developing a correct hypothesis.

Example: A remote site recovers from a power outage.  All of the devices come back online, thus the event is perceived to be over.  Yet for the next few days, performance in that office seems to be slow.  Users in that office have a lot of VoIP call quality problems and call drops, and cloud services seem to crawl and suffer from disconnects.  What happened?  To fix the issue, you need to troubleshoot.

The standard troubleshooting formula
Having a systematic approach to solving the problem will make you a faster and smarter troubleshooter, and in every network nightmare scenario, the faster, the better. The formula at face value is a simple one. Define, isolate, and solve. Once you have checked the basics like making sure it isn’t a physical-layer problem (is it plugged in?), and that the involved devices respond to ping requests, the real troubleshooting starts. Most troubleshooting involves a rule-in and rule-out process to help narrow down the location and cause of the problem.

Troubleshooting steps:

1. Collect information
2. Develop a hypothesis
3. Test the hypothesis
4. Implement a fix
5. Verify the problem was solved
6. Notify the users
7. Document the fix

If I make this sound simple, it’s because it is, for a simple network. However, while vastly more complicated, the formula remains the same in a complex IT environment.

What Type of Information should be Collected?
When collecting information on the problem, it is critical to make sure that you know enough about the scope of what part of the network is included in the problem, and what part of the network can be safely excluded.  Otherwise, you might be stuck forever trying to collect and analyze information that might be unrelated to the problem.

Start by asking yourself the necessary questions to define the scope of the problem:

• Who is having the problem (one user, multiple users)?
• Is it just one application, or all applications?
• Has anything changed?
• Has this happened before, if so, when?
• Can we reproduce the problem?
• Was anything done differently?

Once the issue is defined, try to isolate it. This involves a process of elimination. If a workstation is having connection difficulties, determine if the problem is isolated to that specific workstation, all workstations in that physical location, or if it’s network-wide. If it’s local, you’ve eliminated a ton of unnecessary work, and you’re much closer to isolating the issue. Even if you haven’t yet solved the problem, you’ve now saved valuable time.

If the problem is related to only one particular application, it can be a valuable clue.  For example, if a user has no problems with accessing web applications, but is having VoIP/UC call quality problems, it may be related to queueing or packet loss, or an issue related to a voice gateway or SIP trunk.

Troubleshooting in a complex network
In a data center, the sheer number of technologies that could be the cause of your simple support ticket can cause your head to spin. There are times when troubleshooting will account for up to ninety percent of a network admin’s time. No one wants to spend their time continually putting out one fire only to find another, but there isn’t always a choice. Effective troubleshooting tools and procedures enable you to quickly respond to those crises and keep your network operating as designed.

Faster troubleshooting is better troubleshooting
All engineers engage in troubleshooting but getting to the root cause of a problem is key. This is a different activity than just monitoring a network and requires different information to achieve its goal. Organizations that rely solely on monitoring software end up having problems when it comes to troubleshooting issues in their environment.

Troubleshooting a network can be a manual process, or it can be automated. There are network troubleshooting automation tools that help you swiftly identify the root cause and its location essentially completing the first two (most time consuming) steps so that you can begin working on the solution.

So, what caused the performance problems that resulted from the remote site power outage problem? A duplex mismatch on the Internet router’s WAN link when it came back online caused a significant amount of packet loss that caused the slowdowns and call quality issues.

BASIC COMMANDS FOR NETWORK TROUBLESHOOTING

Ping

Ping is likely the number one utility that every tech pro will use on a daily basis. It helps us to determine two things: latency and packet loss. Because ICMP is typically the lowest priority packet in the pecking order, it doesn’t tell us what the problem is. Instead, it tells us that there is a problem that needs to be addressed. Usually, if there is either packet loss or latency (or both) this can indicate bandwidth saturation over a link or even a bad network cable or port on a switch. Regardless, this will almost always be your first go-to utility when you begin your troubleshooting process. Figure 1 shows ping running in Windows 10.

Figure 1: Ping Tool

9. Traceroute / Tracert

This is probably second in the top three utilities you’ll use on a daily basis. Traceroute is invaluable for telling us what network devices are between one point and another, and gives us some data on what those devices are doing. Some of the extra data it provides are latency values (min, average and max) and host names of the devices, if they’re configured to have them. This also helps us to figure out where these “hops” are, as ISPs typically include some sort of nomenclature to determine which state or country they’re in. On a private network, this may be less obvious. Traceroute can also help to diagnose routing issues, especially when we have more than one network connection to the outside world. Figure 2 shows a tracert in Windows 10.

Figure 2: Tracert

8. Ipconfig / Ifconfig

Rounding out the last three are Ipconfig (Windows) and Ifconfig (Linux / Unix). When we need to know the IP address(es) of the host that we’re working on, these are the utilities to use. Not only will it provide IPv4 information, but it will also provide IPv6 addresses, MAC addresses, DNS servers, default gateways and data with regard to how much traffic is flowing over the interface along with errors and dropped packets. Figure 3 shows the Ipconfig command in Windows 10.

Figure 3: Ipconfig

7. Nslookup

This is a great utility for two things: locating the IP addresses associated with a domain name and checking to see that DNS (Domain Name System) resolution is working for our host. When we enter www.google.com into our web browser, the computer invisibly queries the DNS server to find the IP address attached to that host name. Nslookup has the ability to not only query our configured DNS server, but also to query any other DNS server we wish. This can help us test remote DNS servers for our clients or even for our own ISP. Figure 4 shows a Windows 10 Nslookup.

Figure 4: Nslookup

6. Whois

This one is an oldy, but a goody. Sometimes we want to know who owns a domain name or a range of public IP space. Whois allows us to do this with ease. Whois will give us details about who has registered a particular domain name and often includes contact details for the registrar. Finding out who owns a range of IP space can help us determine where odd traffic on our network is coming from. Windows 10 does not have Whois installed by default, but it’s downloadable from its website. Many other free websites also offer this service. Figure 5 shows a Web based Whois.

Figure 5: Web based Whois Result

5. Netstat

Ever wonder which ports on your hosts are open and listening? Enter netstat. This utility is especially helpful on servers or hosts that run their own firewalls—like SQL Server or Apache. Each uses different network ports to communicate. For instance, if we want to run a web server, but for some reason IIS isn’t “listening” for communications on port 80, it won’t serve up its web pages to anyone. Netstat also tells us who else is connected to our host and on what ports. This can be especially helpful if we suspect that our security has been compromised. We may not see anything in the task manager, but netstat can help us root out a culprit by showing us if there are any strange ports active and communicating. Figure 6 shows a Windows 10 netstat.

Figure 6: Netstat

4. Putty / Tera Term

The need for a remote console cannot be overstated, especially when dealing with Linux or Unix-like systems. A remote console (or terminal) is a must-have for “headless” systems that don’t have a desktop environment. The console is a powerful tool in the right hands and in the Linux/*nix world. It’s absolutely essential for server tasks. It’s also one of the best ways to get into a network with connectivity problems. It takes almost no bandwidth to make a connection and terminal software is very forgiving when it comes to packet loss. Figure 7 shows a Putty session and Figure 8 shows tera term session.

Figure 7: Putty

Figure 8: Tera Term

3. Subnet and IP calculator

Sometimes we just don’t want to be bothered with doing a whole bunch of binary number crunching. There are a multitude of downloadable and free web-based IP and subnet calculators available should we wish to use them. This can be a quick solution when we’re in a hurry and haven’t memorized the proper subnet for a /30 IP range. Figure 9 shows an example of one such calculator.

A web-based calculator can be found here: http://www.subnet-calculator.com/

A downloadable calculator can be found at Solarwinds, here: https://www.solarwinds.com/engineers-toolset/use-cases/subnet-calculator

Figure 9: Subnet Calculator

2. Speed test

Getting to know your bandwidth. If you stream a lot of Netflix at home, you’ll be familiar with the little spinning circle that lets you know that the video is buffering. Oftentimes, this is due to a lack of bandwidth when your roommate is also streaming the latest DOTA match on Twitch. Websites like Speedtest.net help us to determine how much bandwidth we have in and out of our Network. Figure 10 shows an instance of Speedtest.

Figure 10: Speedtest.net

1. IP Scanner

Having an IP scanner is priceless in a network environment, especially when we don’t have login credentials to the router. Being able to scan an entire subnet enables us to find IP addresses of devices that might otherwise elude us. There are many devices on a network that don’t have a quick interface to tell us what their addresses are such as printers and scanners. This can also help us to find devices that have mistakenly been configured with incorrect or duplicate IPs. An excellent IP scanner can be found below as well as an image in Figure 11.

Figure 11: IP Scanner

I have been using all of these tools for many years. The interfaces have changed on some, but others (such as command prompt tools) are exactly the same. There are many switches that come with each tool. For instance, the /t in a ping command does a continuous ping instead of the four pings it would normally do. With Linux, ping will continue without the /t. Understanding the use and value of switches will help you become the fastest and most valued troubleshooter in your office.

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