Troubleshooting Network Connections

– Alex “crazygerman” Byron –

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Summary

Networking has seen a huge gain in popularity over the last several years. Prices for networking equipment have dropped, a whole slew of network products are available for both business and home networking, the majority of new PCs and laptops come equipped with network adapters right out of the box, and setup has become much easier. As a result, many computers are connected to office and/or home networks, both wired and wireless.

As easy as it can be to set up a new network, networks can be complex and involve many parameters and components that can easily be misconfigured or fail. Troubleshooting a broken network connection can be a daunting task for the average user. Following instructions to set up a basic network from scratch is one thing – finding a problem is a whole different story. This article covers a number of typical scenarios of a PC connected to a network and offers a list of logical and straight forward troubleshooting steps for each specific scenario to make the troubleshooting process easier and take some of the scariness out of it.

The instructions and troubleshooting steps found in this article are mainly geared towards computers running Windows 2000 or XP as they are currently the most common Windows operating systems connected to networks. While Windows 9x/ME can also be connected to a network, they are outdated versions of Windows and can be a pain in the ass to get to work on a network. However, even though the examples given are usually Win2K / XP commands, they either will work in other operating systems or have similar equivalent commands. Additionally, most of the troubleshooting steps are generic enough that they apply to other operating systems as well.

When the instructions refer to checking a setting or configuration parameter for a certain piece of hardware such as a gateway device, they are purposely generic as every device is different. It is up to you to consult the manual and figure out how to get to the appropriate menu option or section.

Contents

Networking Basics

Before delving into the troubleshooting process, it is important to understand the basic concept of networking. The purpose of connecting a PC to a network is to exchange data with another PC such as sending an email, viewing a web page, or copying a file. The other PC can be physically close such as in the same room (home network) or the same building (office network), or physically remote such as a web server in a different state or country. The Internet is nothing but a gigantic network of countless computers, all interconnected via a myriad of hubs, switches, routers, and firewalls. By connecting your PC to a DSL or cable modem or plugging into an office network you get access to this network and the ability to exchange data with a number of other machines that are on that network.

To participate in a network, a PC requires the following components:

  • Operating system (or short OS) – Pretty obvious. Without an operating system installed such as Windows or Linux, the PC isn’t good for much.
  • Network application – to participate in a network you need a program that can send and receive data over the network. This could be a web browser, an email program, an FTP client, a Telnet client, a game with multi-player capabilities such as Half-life or Quake, or a chat program such as Yahoo or IRC, just to name a few.
  • Network protocol – All operating systems usually automatically install a networking protocol, normally TCP/IP which is the most common network protocol. There are others such as IPX/SPX, but TCP/IP is by far the most popular one as the entire Internet and the vast majority of all home and office networks are based on it.
  • Network configuration – Every computer that wants to participate in a network, requires a number of pieces of information. Most importantly, it needs an address so it can be uniquely identified on the network. This is just like everybody with a telephone having a unique phone number. This address is called an IP address and could look like this: 10.0.2.25. It also needs a subnet mask which indicates the size of the network, the network number, and its broadcast address. It could look like this: 255.255.0.0. Then it needs the IP address for the gateway. This identifies the computer on the network that passes data back and forth between the network the PC is on and the next network segment. These are the absolute minimum configuration requirements to successfully configure TCP/IP for network connectivity.
  • Network adapter – Also known as network interface card (or short NIC) or ethernet adapter / card. This can be a PCI card inserted in the motherboard of a PC, a PCMCIA card inserted into a laptop, or an external adapter connected via USB. The network adapter can be either for a wired or a wireless network.
  • Driver – No matter which type of network adapter is used, it has to have a driver installed in the operating system. A driver is a small piece of software specific for each OS that is provided by the manufacturer of the adapter. It contains instructions and information that allow the OS to communicate with the network adapter and pass data and instructions back and forth. Depending on the OS and the type of adapter, the driver may be already provided and automatically installed. If not, it needs to be manually installed.
  • Network cable – If the adapter is for a wired network, a cable is required to physically connect the network adapter to a network jack in a wall, hub, switch, router, etc. A network cable is also often referred to as a Cat 5 cable, short for Category 5 which is currently the most common type of network cable. There are two main types of Cat 5 cable: straight-through and cross-over. This refers to the way the 2 of the 4 wire pairs inside a Cat 5 cable that transmit the data are arranged on each end. More details about this can be found in the Cat 5 Do-it-yourself article.
  • A functional network – Of course a working network is required to connect the network cable to. This can be a corporate network in the office, a small home network, or the Internet directly via a broadband connection such as DSL or cable modem. This network consists of more cables, hubs, routers, switches, etc. that all have to be configured and function properly for your data to be able to reach its destination and the reply to return to you.

In a simplified manner, here’s how a data transmission over a network functions. When an application wants to communicate over the network, it cannot access the network directly. It has to format its request according to the rules set by a protocol and pass it down. The request will be handled by several layers which are known as the 7 layers of the OSI model. Each layer will wrap and tag the data package and pass it on to the next until it is finally placed by the network card in form of an electrical signal on the actual wire and transported to the next stop on the way. The packet has to pass a number of “hops”, which are routers that redirect it along the way to help reach its target. Depending on the location of the target, this could be just one or two hops if it’s on the same network, or 20 – 30 hops if it is far away in a different state or country. At the final destination the packet is passed through all 7 layers, this time in reverse order, and finally ends up at the recipient. Here the request gets processed, the reply will be packaged and passed through all layers to be sent back to the originator.

This whole process is pretty complex and could take a book to explain, which is beyond the scope of this article. The point of this summary is to present an idea of how many devices and wires the data has to travel to reach its destination. Given the complexity of networking and the vast amount of components and parameters involved, it’s quite amazing that everything works together so well, enabling us to send and receive data from around the globe in a matter of seconds. However, once something breaks, this complexity comes back to bite us in the ass because there are so many things to check when troubleshooting a network connectivity problem.

 

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