Analyse Your WiFi Environment Objectively #2

When you have a WiFi LAN, and want to find out why it doesn't perform as well as you'd expect to, the first thing most folks will instruct you is

Do a WiFi site survey. Find out what your neighbours are doing.

When a site survey must be done, the best known procedure is to run NetStumbler.

But NetStumbler, for all its highlights of being easy to use, and well known, has shortcomings.

• It doesn't support 802.11n client equipment.
• It doesn't reliably detect 802.11n networks.
• It doesn't run under Windows Vista.

Fortunately, there are new WiFi spectrum analysers, available now, that may provide help where NetStumbler fails. Two such products are InSSIDer (from MetaGeek), and the Xirrus Wi-Fi Monitor Gadget for Windows Vista.

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Powerline Networking - A Cabled Network Without Ethernet Cables

When it comes to networking your home or small office, I like to say "Ethernet for security and stability, WiFi for convenience". Unfortunately, you'll occasionally have a problem where you can't run Ethernet cables, and WiFi won't do the job either. Fortunately, any building with computers, and most without, has a third possibility - one that uses cables already installed - the power cables in the walls.

Ethernet Over Power, or Powerline Networking, is pretty simple. At each location where you need a network connection, you plug an EOP bridge into the wall, and an Ethernet cable connects to that. The other end of the Ethernet cable you connect to a single computer, or to a hub, switch, or router.

There are several vendor choices for EOP bridges, and here are 3 examples.

• Linksys PLEBR10
• Netgear HDX101
• Netgear XE102

Ethernet Over Power has its disadvantages, of which you must remain aware.

1. They have a limited market, so you'll have less choices and you'll find them relatively pricey, as compared to WiFi.
2. They are proprietary - each of the 3 choices above will only work with others in the same product line.
3. They use the 120V power circuits, and on a typical 240V service you will have to ensure that all units are plugged in to the same 120V half of the 240V.
4. Like WiFi, they are half duplex. All EOP devices, even if they will not network together, will still have to share the powerline signal spectrum.

Issue 1 is simple economics. More WiFi components are sold than Powerline Networking / Ethernet Over Powerline. More sales volume = more competition = lower prices = more sales volume. Look at the choices for WiFi, and compare that to EOP.

Issue 2 is unfortunate. The HDX101 and the XE102, even with both made by Netgear, will not participate in a network.

An HDX101 may coexist with HomePlug 1.0 products, but is not compatible nor interoperable with NETGEAR’s XE104, XEPS103, XE103, XE102 or WGXB102 Powerline products.

Issue 3 is a fascinating concern. In a typical domestic wiring system in the USA, you'll have a 240V service, which includes 2 hot leads providing the 240V. There will be a third lead, neutral, such that the neutral and either one of the hot leads, in combination, provides 120V. This is a 240V split service, providing 2 "legs" of 120V each.

Small appliances and light bulbs, in the USA, use 120V. With a 240V split service, half of the appliance / lighting circuits will be on one hot lead (1 "leg" of the service), and the other half on the other leg, providing a balanced load. When you setup your EOP bridges, they will all have to be on the same 120V leg, or there will be no signal between the bridges.

Essentially, you could (unreliably) have two EOP broadcast domains. All EOP devices on one leg will irregularly receive signals from the EOP devices on the other leg. When you turn on your kitchen stove, or other 240V appliance, you may get signals from one leg to the other; at other times, both legs will be isolated. If you don't plan for this to happen, you will learn it the hard way.

To identify which legs your prospective EOP bridge locations are on, examine your circuit breaker box. First, identify the breaker servicing each location. Verify the proper breaker, by plugging a lamp into the outlet, flipping the breaker, and watching the lamp go off then on. Having verified the breakers, examine their relative locations. Most breaker boxes will have the breakers arranged in two vertical columns, with alternating rows of breaker slots on different legs.

If you have two breakers vertically adjacent (in either column), it's likely that the two circuits will be on different legs. With breakers separated by 1 breaker slot, they will be on the same leg. With breakers separated by 2 breaker slots, they will be on different legs. And so on.

Note that two breakers, separated by a double width breaker (240V circuit, occupying 2 slots), will still be on opposite legs. Two slots (one double width breaker) is the same as two slots (two single width breakers); and the two breakers on opposite sides of the two slots will be on different legs.

Issue 4 is similar to WiFi. All EOP devices on the same service will have to asynchronously share the powerline signal spectrum, regardless of product line, and only one device can transmit at any time. The more EOP devices you have, the less efficient your powerline network will be. Despite different product lines being incompatible with each other, they all still have to share the powerline spectrum, as peers.

Despite the above problems, though, Powerline networking is a good solution when you can't run Ethernet cables, and when you can't get a WiFi signal to reach.

Note that EOP, for computer networking, is a relatively new technology. X-10 Remote Control Appliances / Lighting, which also sends signals over the AC power grid, is not. The problem of signal propagation on a 240V split service has been a long time problem for X-10 owners. There may be X-10 solutions that are usable in EOP scenarios. It's also likely that EOP and X-10 may be incompatible, on the same service or in the same neighbourhood. X-10 also makes remote (wireless) stereo speaker systems, which may present the same challenge.

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New Equipment In Your LAN

Every week, someone writes for advice

I just got a new router, and now I can't access my computers from each other.

or

I just got a new router, and none of my computers can access the Internet.

Frequently, the cause of these problems will fall in two categories - new features, and settings.

New Features
Many new, and high end, routers come with protection that emphasise Internet access, and make file sharing an optional activity, to protect the individual computers from each other. Look carefully in the Owner's Manual, for a "DMZ", "Isolation Mode", "Virtual Server", or "VLAN" setting - either on a single port, or affecting the entire LAN.

And if you are setting up a WiFi router, make sure that the radio is turned on. Some WiFi equipment is delivered with the radio turned off, to ensure that you will intentionally activate it, and be prepared for when this is done.

Settings
Any time that I was changing my network equipment, I would take a snapshot of all network settings from all computers. You can never tell when this might be a life saver. Logs from "browstat status", "ipconfig /all", "net config server", and "net config workstation" could all be useful when troubleshooting. Make a set before, and after, any change. Compare each, line by line, and if you spot any differences, explain or fix them before continuing.

If you're having trouble accessing the Internet, check to see if your computers are using manual assignments. New equipment will probably include an IP address change for the router - some vendors provide a default LAN on 192.168.0.0/24, others 192.168.1.0/24, and others have additional variations. Maybe the router handles DNS differently too.

If you're having trouble with Windows Networking, either an Error 5 aka "Access Denied" or an Error 53 aka "Name not Found" may be seen, or you may simply not see any computers in Network Neighbourhood. If this is the problem, check the security components on the computers - since a new router will probably result in a new subnet address, check personal firewalls and anti-worm programs, for settings that are IP address sensitive.

If All Else Fails
Get into Troubleshooting Internet Connectivity, or into Troubleshooting Network Neighbourhood, depending upon the problem being observed.

And of course, make sure that the new router has the current firmware, obtained from the vendor.

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Windows Vista And Routers

As I've written separately, the networking stack in Windows Vista is significantly different from the networking stack in previous versions of Windows. These differences are discussed, in detail, by experts like Joe Davies of Microsoft.

Like any improvements, the many improvements in networking, in Vista, use more resources - memory and processor - on the host computer. Resources on any peripherally connected computer - or router - will likewise be used more intensively. In testing Vista, Microsoft engineers found out that older routers won't perform as well when used with computers running Vista, as with computers running earlier versions of Windows.

As you integrate your computer running Windows Vista with the rest of your network, you'll find a few challenges with the various computers running other operating systems. Those differences you'll have to work around, with configuration changes.

If you get a new computer running Vista, and your router is a few years old, it's time to replace the router too. Or at least upgrade the firmware - if any is available - obtained from the vendor.

For more discusssion:

• CompatDB.org Forums: Problem with Wireless causing Router Resets


• Mike Salsbury: The Windows Vista Experience


• MSDN: Weird one - Router Death by Vista


• PChuck's Network: AutoTuning In Vista Maybe Not Ready For Prime Time

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The Weak Point In Your Internet Service - The Power

If you have a typical Internet service, you likely (hopefully) have 2 mysterious network devices, connected between your computer and your ISP's service.

• The modem (dialup, cable, or DSL) connects directly to the wire coming out of the wall.
• The router connects between the modem, and your computer.

Both the modem and router have power supplies - also known as "wall warts", because they have big plugs - 3 - 4" cube shaped, that make it hard to find a power outlet with room to plug it in. If you have these, you should know what I mean.

Recently, I thought that my router was slightly faulty. Several times / week, I was losing Internet service, even though the diagnostic lights on my DSL modem, and the router, were normal. Restarting both the modem and router would restore my service, but only until the next time.

I bought a universal power supply at Radio Shack for $15 or so, and swapped it for the power supply for the router for a while, but saw no improvement in the symptom. Service was going out too frequently - first a couple times / week, then daily, and finally multiple times daily. I put the vendor power supply for the router back in service, took the replacement universal power supply, and tried it on the modem, and the problem was solved.

It's summer time here in North America, and I'll bet heat sensitivities are part of the problem. If your Internet service has been acting up on you for a few weeks, and you've been pestering your ISP with no results, check your equipment, and start with the power supplies.

In this situation, the "universal power supply" is a key item. Each different electronic device - modem, router, or what have you, will have differently designed power requirements. Plug size, polarity, and voltage will differ from device to device. In my case, my modem uses 6V DC +, and my router uses 12V DC +. Being able to try the same power supply on both units, by simply changing the switch on the wall wart, made it possible for me to solve my problem.

When you setup the power supply for your modem or router, read the instructions carefully. Plug size (6 choices) is obvious. Polarity and voltage are not obvious, but getting them right is essential. In most cases, the wall warts from the vendor will have clearly labeled requirements, with both polarity and voltage obviously described. Carefully following the instructions with the replacement power supply, you can swap units in a couple minutes.

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Driver Problems Causing Intermittent Network Problems

Recently, on computers running Windows Vista, and occasionally on computers running Windows XP, you might start the process of copying a relatively large file from one computer to the other. The copy process starts out smoothly (ruling out complex issues like name resolution, or permissions, or even visibility).

Well into the copy process, with several Megs of file content copied, the process abruptly terminates with a monolithic message

The network location is no longer available

Well, what now? Did the other computer go off the network?

So, you start layered diagnostics.

• Check physical issues.
• Check name resolution.
• Check permissions.

And, you find no problem, with either the copy source, or target. Maybe you try copying in the other direction, or start the copy from the other computer, and sometimes this will make a difference.

Frequently, the cause of this problem will be simple. With Windows Vista having been on the market for a rather brief amount of time, the vendors of the various networking adapters are still developing drivers for their products. Either the vendor of the network adapter in your Vista computer has not produced a driver specifically written for Vista, or the driver produced has not been sufficiently tested.

So now, you contact the vendor, and ask about a newer driver. But go to the vendor, not to Microsoft.

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No WiFi Connectivity? Check The Power Settings

So you just got yourself a new laptop computer, and of course a WiFi router so you can use the new computer while lying in bed (no we won't discuss why you want that). And you followed all of the instructions, and you run the WiFi client setup where it lists networks for you to connect to, and you see

No wireless networks are within range.

Dohh! Guess you won't be surfing the web from the bed after all.

But before you give up, and take it all back to the store, check everything again. To start, check power. There are up to 4 power settings, and yes, I will describe the obvious ones too.

• The laptop has a power switch.
• The router should (but probably doesn't) have a switch. But check the power cord. Of course, since you just ran the router setup (connected by Ethernet cable), the router must be on. OK, move on.
• If the laptop has built-in WiFi, it's got a power switch for the radio. The radio is the part of the WiFi device that uses the most power, so every laptop lets you turn the radio off. Most laptops ship with the radio turned off, so you won't use it without knowing that it's on. Read The Manual.
• Check the router setup, and make sure that the radio there is on. Most WiFi routers ship with the radio turned off, so you don't set one up, with the radio on, without knowing that it's on. This keeps you from inadvertently providing free Internet service to your neighbours. Again, Read The Manual.

Always check the power, after you set everything up. Then check all of the physical issues again.

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Electrical Issues In Ethernet Networking

If you wire your house with Ethernet, you'll have a houseful of computers, all connected to the power system, and all connected to each other through the Ethernet network, and through the electrical system ("mains"). This is an obvious, but not trivial, issue.

With all computers connected within the same building, it's not a major issue. All computers are connected to the same main power supply, fed through the same power feed from the electric company, and grounded at the power distribution panel (electric meter et al). All computers, on properly maintained electrical and Ethernet networks, should have the same ground potential.

If you're lucky enough to have a large property, maybe you have a garage or shed out back of your house, with a separate electrical feed. If you decide to install a computer out there, networking that computer won't be a trivial issue. Getting past the issue of running cable between the two buildings (bury it, and risk underground problems), or string it through the air (and risk birds and other wildlife damage), you have a major code and safety issue.

Two separate buildings will have different ground potentials, amplifying the damage from lightning strikes. To fulfill electrical code requirements, you must ground electrical feeds, to separate buildings, separately. If you run Ethernet cable between your buildings, and lightning were to strike one building, the lightning would possibly travel from one computer to the other, through the Ethernet cable, and eventually to ground at the other building.

If you were unlucky enough to be working at either computer when this happened, you'd probably not live to worry about it. If you were lucky enough to not be in front of a computer, you could at least kiss the computers goodbye.

Even ignoring the possible damage from a lightning strike, a computer network with different computers connected at different ground potential won't do much for network stability. A properly functioning network depends upon ground at every network point having the same (identical) voltage level. Any variances, as can happen between any two separately grounded objects, will cause chronic and intermittent packet loss.

The bottom line? If you can't ground both ends of the Ethernet cable very securely, fiber or WiFi is a much better choice for connecting two separate buildings. Fiber-Optic cable doesn't conduct electricity, just light. And WiFi isn't a physical media at all.

If you have 2 buildings, limit the dangers of lightning to each building alone. Don't tie the two together, inadvertently.

For more discussion:

• Cabling Installation & Maintenance: Ground potentials and damage to LAN equipment
• Citel: Overview of Transient Overvoltages
• SelfHelp Forums: Cat 5 between buildings

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Connecting Two Dissimilar Networks, Intentionally

Microsoft Windows operating systems in general, and Windows NT (2000, XP, 2003) in particular, use Internet Protocol for connectivity. In most cases, when I'm providing advice about connecting two dissimilar networks, I'll advise using a router.

• With two different networks, using a different medium, the differing nature of the network traffic justifies use of a router, for efficiencies sake.
• With two dissimilar networks, with differing security levels, the security differences justifies use of a router.

But what about those cases where you own and control both networks, and you intentionally want to keep the traffic on both networks equal? If you have a LAN, you want all computers on the LAN to be able to access each other, seamlessly. But Windows Networking in general, and NetBIOS Over TCP in particular, doesn't pass thru a router transparently.

What you need is a simple switch, but for two different network mediums. And that is called a bridge.

Now if you do WiFi, you may have already read about making a WiFi bridge from a NAT router. That's a standard solution. But what if you only have a computer, but with 2 different network connectors? Pick 2 of any:

• Ethernet.
• Personal Area Network.
• WiFi.

If you have 2 computers, and a network, and only one of the 2 computers has the proper equipment to connect to the network, but both computer can connect to each other, what do you do? If the one computer (with 2 connections) is connecting to a public network, and the second computer needs access to that public network, you can run Internet Connection Sharing on the first computer.

But ICS provides a routed connection. When the first computer is connecting to a public network, connecting the second computer thru a router makes sense - a router is the outer layer in a layered security strategy.

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Centralised (Structured) Wiring In Your Home

If you have two computers, you connect the two computers with a single cable, Computer A to Computer B. I'll bet (hope) that you don't have just that, though. You probably have at least one more computer - your router (which is connected to the broadband modem). So you have a cable from the router to each computer. This is assuming that you aren't using WiFi to connect either computer, and again I'll point out that WiFi is not a good substitute for Ethernet cable.

So you have your router, and a couple computers, in the same room, and you run Ethernet cables between them. But are all computers in the same room? Not if you have a well planned house. You'll probably have one or more of

• An office computer, for financial and secure activities.
• An entertainment computer, in the den / family room, for fun.
• A second computer, in the den / family room, for music / videos, with a large screen (what used to be called a television / stereo / home entertainment center).
• In your kitchen, you need a computer for recipe access, maybe for inventorying and ordering food.
• How about one in the garage, for reference when you work on the car?
• The bedroom, for late night web surfing (no, we won't discuss that any further).

Now, there are so many reasons why having separate computers, with different designs, will be relevant.

• Locational convenience. Why walk into another room, to use a computer in there, if you have one in front of you?
• Redundancy. One computer will not last forever. Maybe last year's office computer is now in the bedroom, and your first computer, old and grungy, is in the garage. If one computer dies, it will be inconvenient to walk into the other room to continue the current activity, but you can do that easier than having to fix the one computer on the spot.
• Security. The web is full of dangers. Each different website may have its own dangers, and I'd bet that different types of websites will focus those dangers. Restricting different activities to different computers makes sense. Keep your office computer, with financial secrets, safe and secure, by keeping it very clean. Other computers, other activities.
• Sharing house space. One person can be in the office, doing financial chores, another in the garage, doing auto or home maintenance, and a third in the kitchen, preparing a meal. And each using a separate computer.

So now that we've admitted to needing computers all over the house, how do you plan to wire them to each other? One long cable - Garage to kitchen to den to living room to office to bedroom? Please don't do that.

Any properly planned business has one or more centralised and secured rooms for wiring and for central equipment (servers). The home of the future will too. The hub room will be where the video communications ("cable TV") and voice communications ("telephone") services will enter from the outside. There you connect your internal cabling. And from there, you make home runs to each room.

This is where you start. More and more homes are being built, with network cabling designed and installed just as coax ("television"), electrical, and voice ("telephone") cabling is. A requirement, not a luxury.

• Bob Catanzarite: Structured Wiring How To


• Total Voice Control: Residential Wiring For The New Millennium

And by the way, if your garage (or maybe a shed) happens to be separate from the house itself, be aware of one specific wiring safety issue.

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What Is A CrossOver Cable, and Why Do I Need One

In any conversation between two people or computers, you speak and the other listens. Or it speaks, and your computer listens. This means that your mouth has to connect to the ear on the other end. This is called cross-over.

If you look at any hub / switch / router 10 years ago, you would probably see the various ports labeled "X-1", "X-2", "X-3"... This meant those were cross-over ports. Your computer would speak (transmit) thru a pair of wires in the Ethernet cable. When the connection went into the router port at the other end, the cross-over function connected the transmit wire pair from your computer to the receive port at the other end, and the receive pair from your computer to the transmit pair at the other end.

If you had to connect a pair of routers directly to each other, you would have a cross-over port at one end connecting to a cross-over port at the other end. This would cause a cancellation of the cross-over function, so you would use a cross-over cable.

If you connected a pair of computers directly, you would similarly need a cross-over cable.

This meant that everybody with a computer network had to have cross-over cables handy.

To eliminate the need for using cross-over cables, router manufacturers developed Auto-MDIX. A router port with Auto-MDIX will listen to see if it is connected to another cross-over port, and switch itself to non-cross-over mode if necessary. Some computers, likewise, have Auto-MDIX. If you connect a pair of computers directly, and one (or both) have Auto-MDIX, you can use a straight-thru (aka patch) cable, and they will connect just fine.

Auto-MDIX is a significant development, in the networking world. Having said that, I don't believe that Auto-MDIX can be relied upon, as a complete solution. I will still advise you to have a cross-over cable, or connector, handy for diagnosing network problems.

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Your Neighbour's WiFi

One of the limitations of WiFi is that it's not scalable, and it has a finite capacity. You cannot get more than (currently) 108M bandwidth. You simply won't be able to stream the latest movie in 3D multi-colour to every media computer in your house without seeing some performance limitations. And that is your own performance limitation. If your neighbour has a WiFi LAN, you will also have to share the bandwidth with him (her). WiFi simply does not have unlimited bandwidth, new technology or not.

In any domestic situation with neighbours, for a problem like a loud stereo, the tendency is to turn your own stereo up. Crank that sucker. This is, however, not a good, long term solution.

• You possibly have up to 8 immediate neighbours, and more beyond them. Some of those neighbours, also currently suffering from your neighbour stereo, now have to suffer from yours too.
• Your neighbour will probably turn his volume up yet again, to overcome the new "noise" from your system.

Like every analogy, this one suffers from a major problem. With loud stereos, it's easy to find where the noise is. Just follow your ears. Then call the police, and have them deal with the problem.

If your neighbour has a "loud" WiFi LAN (ie SuperG or MIMO), you won't be able to follow your ears. Nor will, I suspect, the police be interested in becoming involved. You're going to have to find your neighbour, and you're going to have to convince him to turn his stereo (WiFi) down. Or suffer in silence.

You can start with NetStumbler, and triangulate the problem. Then, you'll have to use diplomacy, not technology. You'll not solve the problem by getting a high power AP.

I, and others like me, have seen this situation coming for some time. Here is one possible real life example, and here is a second possible real life example. And even if neither discussion is diagnosed with this cause, this scenario is coming. Channel saturation, and unexplainable intermittent bandwidth variation, will become the norm, not the exception.

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Choose Your WiFi Client Manager Carefully

When I got my laptop, it came with built-in WiFi, and with 3 programs ("Client Managers") to manage the WiFi connection.

• HP - The laptop vendor.
• Intel - The WiFi card vendor.
• Microsoft - The operating system vendor.

The problem is, only one program can manage a WiFi card at any time. Multiple managers = confusion = random disconnects. Each Client Manager program will be different.

• Information displayed.
• Organisation of wizards to make settings changes.
• Security options.

The Microsoft product, Wireless Zero Config, has one major advantage. WZC runs as a service. If you depend upon your computer having connectivity without you being logged in, or even immediately after you login, you may find this a useful feature.

Just make sure that only one client manager is run, at any time.

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Analyse Your WiFi Environment Objectively

When you setup a network of computers, in your home or small office, a mass of Ethernet cables running everywhere can be a problem. WiFi, or Wireless networking, can provide relief from the mass of cables. But WiFi is not an effortless replacement for Ethernet. Installing a WiFi network takes careful preparation.

There are many reasons why you won't get the expected bandwidth from any WiFi network. Some of them you can correct, others you can't. And sometimes, even without you making any changes, you'll have problems. All the planning you do is useless when your neighbours install a WiFi LAN next door.

With all of that in mind, you need to evaluate your WiFi environment objectively, both before setting up a WiFi LAN, and after. When "it stops working", find out why. When your Ethernet network stops working, you can start with a simple IP scan of the subnet. With a WiFi network, you have to go a level deeper than Internet Protocol (sometimes, IP may not even be relevant).

There are many tools to objectively analyse your WiFi network; some are free, others cost good money. Here are but two.

Netstumbler makes a free, lightweight WiFi spectrum analyser from your computer and WiFi adapter of your choice. Netstumbler continuously scans the WiFi spectrum covered by your WiFi adapter, identifying each WiFi network device (whether access point / router, or client), and recording a dozen or so metrics about each network device found.

NetStumbler has two displays, both very useful. The display that you see immediately is the AP inventory, which enumerates each AP observed, and includes over a dozen very useful details about each. But you can discover more.

If you identify an interesting AP from the main list, you can find the MAC address for that AP. From a tree entry in the left column, you select a specific MAC address, and you can observe a running signal to noise graph for that network device.

Netstumbler, though free, and easy to use, has disadvantages.

• It does not work with every known WiFi adapter.
• It does not analyse non WiFi signals. If you have a cordless phone, microwave oven, or nearby ham radio operator, NetStumbler will show those merely as "noise", as part of the signal to noise ratio for any WiFi network device.
• NetStumbler binds to the WiFi adapter just like any other WiFi client. If you run NetStumbler while you're attached normally to your network, using WiFi, you'll experience the same instabilities as when when you run multiple WiFi client managers.
• It's not compatible with Windows Vista.

The Wi-Spy Spectrum Analyzer overcomes some of the disadvantages of Netstumbler. The Wi-Spy is a USB dongle / WiFi receiver, that will receive and analyse signals in the WiFi spectrum.

• It does not require an add-on WiFi adapter, and has no compatibility problems like NetStumbler.
• It provides the same sort of analyses about all detectable WiFi network devices, as NetStumbler. Also, it analyses the noise (signals from non-WiFi devices) in the spectrum, and attempts to identify the device producing the noise, from a database of known interference sources.
• It works with Linux, Mac, and Windows (Windows 2000 or XP, and yes, Vista).
• It is not inexpensive, but it is worth the price.

Note that NetStumbler has its shortcomings, in lack of support for new technology. Fortunately, alternative products are available.

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A Set Of Simple Network Components Definitions

Many folks, when they start connecting their computers, get lost in the terminology. Justifiably so, I would think. I can hear the pain in their voice.

• I want to connect my computers. One guy in the store showed me a hub. Somebody else told me to buy a switch. And in the forum, I was told that a router was the only way to go. Help!
  
• I want to connect my computers, but avoid using cables everywhere. One guy told me to buy a wireless router. Somebody else recommended an access point. And I hear about bridges, and repeaters.
  

• Introduction to Networking
  
• Wired Devices - Bridges, Hubs, Routers, and Switches.
  
• Wireless Devices - Access Points, Bridges, Repeaters, Routers, and Switches.
  
• Summary and References
  

Introduction to Networking
To learn about network components, and what each one does, you first need to learn the concept of the OSI network model. All network components are defined in term of the network layer which they work in. Components in any one layer connect to other components in that layer, or to components in the layer above or below.

A network cable would be an example of a component in the Physical, or bottom, layer. Ethernet, which is one of the most common network standards in use today, incorporates both the Physical Layer, and the Data Link Layer. An Ethernet cable, then, connects thru both the Physical (Layer 1) and Data Link (Layer 2) layers, and can connect to a Network device, such as a router.

Routers, which operate at Layer 3, connect networks that use Internet Protocol (IP). For intensive instruction in IP networking, see Microsoft TCP/IP Fundamentals for Microsoft Windows.

WiFi, which is not a totally physical medium, is similar to Ethernet, excepting that it uses a radio channel, instead of cable.

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Wired Devices - Bridges, Hubs, Routers, and Switches

Hubs, routers, and switches are devices used to connect computers, that are physically attached (using cables), or logically attached (using WiFi).

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A hub is one of the most basic network components; like a cable, it is a Physical (Layer 1) device. It is not addressable, it connects passively to a group of Ethernet (or other media) cables.

A hub effectively connects a group of computers in one big conversation, much like an old fashioned telephone party line. With all computers in a network connected by hubs, only one computer will be able to transmit, to another computer, at any time. Computers connected in this way must use a communications technique called Carrier Sense Multiple Access/Collision Detection (CSMA/CD).

CSMA/CD is a pretty inefficient protocol. If you are chatting with a friend, maybe over the telephone, do you ever notice that sometimes one of you wants to speak when the other is still talking? How about if both of you start talking simultaneously? What if a group of you, and many friends, try to carry on a conversation that way? Sometimes, you have to spend as long deciding who's going to speak next, as actually speaking.

In effect, with a hub connecting your computers, the more computers that get connected, the less productive network work will get done. Hubs are just not scalable - that is, you can't keep adding computers to a hub, and get any decent production out of a network.

Since the purpose of networking computers is to transmit massive amounts of data between those computers, the switching hub was developed.

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A switch is a Data Link (Layer 2) device. A switch, which was originally called a switching hub, connects specific computers to each other selectively, much like a telephone switch, for individual conversations. Individual computers are addressed (selected), by a switch, using their MAC addresses.

With a switch, individual pairs of computers can carry on simultaneous conversations. Essentially, a switch is to private line telephone (which is the telephone service we all take for granted) as a hub is to party line telephone (if any of you are old enough to remember that). A switch operates in full duplex mode (each computer can send and receive simultaneously), where a hub operates in half duplex mode.

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A bridge is a type of switch. Where a switch, in general, connects two or more networks that use identical media (such as Ethernet), a bridge may connect networks that use different media. In Internet connectivity, a modem will act as a bridge, and connect:

• The Public Switched Telephone Network (PSTN) to a serial cable, leading to a computer or router (or connect as an internal component in your computer). A properly selected NAT router (though not all NAT routers) can connect to a properly selected external modem.
  
• A cable broadband network to Ethernet, or USB cable.
  
• A DSL broadband network to Ethernet, or USB cable.
  

A WiFi Bridge connects (bridges) Ethernet to WiFi.

There is one other difference between a bridge and a switch. A switch, by definition, connects multiple computers, and has 4 or more ports. A bridge generally connects only 2 different networks, and has 2 ports. A bridge with more than 2 ports generally has a hub or switch attached to one of the bridge ports.

Since the MAC address is factory assigned, and intentionally unique in all circumstances, it would be practically useless to designate groups of computers by MAC address. Switches are more effective than hubs for connecting large groups of computers, but the groups need to be local to each other for efficiency.

To associate groups of computers, where not all groups are local to each other, you need the ability to associate computers in location based groupings. This is where Internet Protocol addressing comes in to use - the IP address is assigned by physical grouping of computers.

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A router is a Network (Layer 3) device, that connects networks that use Internet Protocol. A router connects specific computers to each other selectively, like a switch. Unlike a switch, which addresses individual computers by their MAC addresses, a router addresses computers by their IP addresses.

Since a router addresses computers by their IP addresses, a router only transports Internet Protocol traffic. IPX/SPX and NetBEUI, which are alternate transports, do not produce routable traffic. Networks which use either alternate transport must be connected by hubs or switches, they won't work with routers.

Since Ethernet connects thru both the Physical (Layer 1) and Data Link (Layer 2) layers, an Ethernet cable can connect either a hub (Layer 1), a switch (Layer 2), or a router (Layer 3). A group of computers, connected by Ethernet or WiFi, thru a collection of hubs, switches, and routers, makes up a Local Area Network (LAN), or a Wide Area Network (WAN). Since the IP address is assigned to each group of computers based upon their physical location, all computers in one physical location can be easily identified by IP address grouping, or subnet.

A router is essentially a big switch, with multiple connections, each connection leading to one or more subnets. A subnet can be locally attached (by Ethernet), or distantly attached (by a long distance communications line). By knowing what subnet is accessible (immediately, or distantly), from any connection, a router can decide which connection should be used for a packet destined for any given IP address or subnet.

Now if you are buying, or just bought, a router for your home or small office, you probably are looking at a NAT router. A NAT router has the functionality of a regular router, and more. For a description of a NAT router, please see my article What Is A NAT Router?.

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Wireless Devices - Access Points, Bridges, Repeaters, Routers, and Switches

A WiFi channel is similar to a hub, in that all computers using a single WiFi channel have to share it with each other. They can choose not to listen to the conversations of their neighbors (properly designed software won't participate in conversations which don't apply to the network that it connects to), but you should not assume this to be true in all cases. You absolutely must practice WiFi security.

And whether or not a WiFi device listens to a conversation on another network, it won't be able to use the channel, while the other network is using the channel. The WiFi channel can only be used by one conversation at any time. All WiFi devices, within range of each other (able to detect radio from each other) have to share the channel, and only one device can transmit at any time. This is why we say that WiFi is a half duplex medium.

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A WiFi router is similar to a wired router, but with one extra component - a radio connected to the LAN switch. The computers that connect by WiFi become peers to the computers connected to the Ethernet LAN ports.

All computers connected directly to the Ethernet switch have the capability of multiple simultaneous, full duplex, communications, with all other computers connected directly to the Ethernet switch. All computers that connect by WiFi, though, have to share the channel with all other nearby WiFi devices.

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A WiFi bridge is similar to a wired router, but with one extra component - a radio connected to the WAN port. Like the wired router, all client computers connect to the bridge by Ethernet.

All computers connected directly to the Ethernet switch have the capability of multiple simultaneous, full duplex, communications, with all other computers connected directly to the Ethernet switch. Connection to the rest of the network, thru the WiFi WAN port, will have to share the WiFi channel with all other nearby WiFi devices.

You can buy WiFi bridges made for that purpose, and some WiFi NAT routers can be converted to bridge configuration. The Linksys WRT54G, with third party firmware, can be configured as a bridge.

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A WiFi access point is a wired switch, with a radio. As with a WiFi router, the computers that connect by WiFi become peers to the computers connected to the Ethernet LAN ports on the switch.

The computers connected to the Access Point - both wired and wireless - will have the same capabilities and restrictions as those connected to a WiFi router.

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A WiFi repeater is, simply, a radio that alternately receives and sends. Placed at a distance from a WiFi router (at a midpoint between the router and the clients), a repeater can extend the range of the router. A repeater that operates on one channel, though, will be very slow. It has to:

• Receive a packet from one WiFi computer, that's intended for another.
  
• Retransmit (repeat) the same packet.
  
• Wait for a reply from the computer that the packet was intended for.
  
• Pass that reply back to the sending computer.
  
• Receive another packet from the sending computer.
  

Summary and References
All equipment, excepting the NAT Router component of any device, operates at Layer 2 of the OSI network model. Excepting the NAT Router component, all equipment will transport IPX/SPX and NetBEUI network traffic, in addition to IP traffic.

Any configuration of equipment, done thru your browser, will typically require Internet Protocol though. Most network components, when designed to be managed thru the network, is addressed (managed) by IP address. Both WiFi routers, and Wired Routers, will only transport IP traffic.

For additional discussion about wired components, see Hard Forum Networking FAQ Q1.

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Proper Network Design

Setting up a network of computers is a lot of fun, even if you're getting paid to do the job. But maintaining, and using, a properly designed and setup network is a lot more fun than maintaining, and using, an improperly designed one. Be aware of some common pitfalls. Proper design, in many cases, is cheaper, and less complex, in the long run.

• Cabling. Making your own Ethernet cables may look like fun, but it's not.
  
• Grouping. Setting up a domain is not for everybody, but it will make your life easier in many ways.
  
• Networking. Using a NAT router for connecting just one computer to the Internet, or for connecting just 2 computers to each other, is cheaper and safer in the long term.
  
• Wired or Wireless LAN? Using WiFi is great - when you truly need it. But know the limitations.
  
• Firewire / USB Networking. In a pinch, a Firewire or USB port can work as an emergency network device. But they aren't good long term solutions.
  

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Ethernet Cabling - It's Not A Good First Time Project
An Ethernet cable is more than a simple group of small wires - it's actually an electrical system in its own right. The specifications for a 10M Ethernet cable are pretty complex - for 100M cable, you have to be more careful. And Gigabit Ethernet cable requires special equipment.

If you're a professional, and setting up a large office, hire an experienced and licensed electrician. If you're setting up your own small network, whether for a small office or for your home, and you're just starting with Computer Networking, buy premade, and tested, cables at a computer store.

Don't learn computer networking starting with making your own cables. Setting up an infrastructure, using reliable cabling, is cheaper, and easier in every respect. Don't start with do-it-yourself Ethernet cabling, when you're setting up a network.

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Domain vs Workgroup - A Little Effort Can Go A Long Way

Every Windows computer will act as a server, but only computers running a true server Operating System - Windows 2000 Server, or Server 2003 - can provide a domain. And setting up a domain is not a good project for your first network. But domains have their advantages as well as disadvantages.

If you have any network expertise, and a server operating system, consider setting up a domain. It's good for you, in the long run.

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Networking Computers Is Cheaper, and Simpler, With a NAT Router
If you have one computer, sitting in your office, and connected to nothing, you have just one computer. If you connect that computer to the Internet, or to another computer, you have a piece of, or the beginning of, a network.

• The simplest way to connect your single computer, to the Internet, is to connect the modem (Cable, dial-up, or DSL), externally, to your computer. Or install the modem internally.
  
• The simplest way to connect your two computers, to each other, is to connect them using a cross-over cable. Using a pair of WiFi adapters, one in each computer, you could eliminate the Ethernet cable, and have an ad-hoc WiFi network.
  

In neither case is this true, in the long term.

• Using a NAT router to connect as few as one (as well as multiple) computers, to your Internet service, is an essential component in layered security.
  
• Using a NAT router to share Internet service, between as few as two (as well as multiple) computers, is almost as cheap as using ICS. And it's far simpler. ICS was a good idea long ago, but it's not today.
  
• Using a NAT router to connect your computers, and / or to share your Internet service, is easily scalable. When you get your second (or third or whatever) computer, just connect it to an available router port. How do you do that with ICS and a cross-over cable?
  

When you get your first computer, buy your first NAT router. And make sure the router can share the Internet service.

• If the Internet service is dialup, make sure that you get an external dialup modem, and a router capable of handling dialup.
• If the Internet service is broadband, cable or DSL, make sure that you get a broadband modem with an Ethernet port. If the modem only has a USB port, get a better modem.

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Choosing A Wired or Wireless LAN Is An Important Decision
When you setup a network of computers, in your home or small office, a mass of Ethernet cables running everywhere can be a problem. WiFi, or Wireless networking, can provide relief from the mass of cables. But WiFi is NOT a replacement for Ethernet, for many reasons.

• Scalability. With a 100M Ethernet cable, you could have up to 200M of data flow (with send and receive simultaneously), between a single pair of computers. Each pair of computers in your office can conduct a separate, yet simultaneous, 200M conversation.
  
  With 54M WiFi, all of the computers in your home or office, and all of the computers in your neighbors home or office, will all share the same 54M channel. Actually, there are 3 54M channels - but if you have even 1 neighbor, chances are that you'll have more than 3, so you'll have to share with at least one other network. And all of your computers will share that one 54M channel. The 54M channel is not a maximum - a 108M channel is a possibility. But there are limitations to that possibility.
  
  And there are other factors which will prevent you from getting an actual 54M, let alone 108M, of data flow.
  
  
• Security. Ethernet cables stay in your home or office - when you lock your door, your cables, and computers, are secure. The WiFi signal, on the other hand, travels thru your walls, and down the block, to your neighbors computers. You have to use extra security precautions, with a WiFi LAN.
  
  
• Stability. Your WiFi neighbors will come and go, constantly. You have WiFi devices politely, and impolitely, sharing the channel. And, you'll have noise on the channel. Noise can come from many electronic sources.
  
  
  
  • Baby monitors.
    
  • Computers.
    
  • Cordless phones.
    
  • Microwave ovens.
    
  • Wireless stereo speakers.
    
  
  

If you truly need WiFi, then use it. The convenience of surfing the Internet from your bedroom is great. But know the limitations of WiFi, before investing a lot of time, and money, needlessly. For many LANs, Ethernet cabling will always be a better solution, excepting for one specific electrical code and safety issue.

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Firewire / USB Networking
Ethernet and WiFi are two dominant standards in networking. Ethernet for massive bandwidth (10G networks are coming closer), and WiFi for convenience. They both have tradeoffs.

Now just about any desktop computer that you may buy today will have an onboard Ethernet port. Most laptops that you buy will too, and most laptops will also have WiFi. And both desktop and laptop computers have a third networking possibility - Personal Area Networking, aka Firewire / USB. Firewire and USB are competing standards. Most computers will have one, if not both, ports. These ports allow you to connect most modern computer peripherals, such as a keyboard, pointing device (pka mouse), even a portable mass storage device (pka disk drive).

Properly designed Firewire / USB devices will use drivers already installed in Windows, and will support hot plugging. You'll be able to connect or disconnect such a device with the system running, at a moments notice.

And that's the strength of Personal Area Networks - the ability to attach and remove any accessory to your computer at will.

Now a PAN is a client (peripheral) - server (computer) relationship. The client attaches to the server (peripheral to computer). Networking computers is more or less a peer - peer relationship. But it's possible to buy a Firewire or USB cable, with an embedded hub, that will act like a client to the PAN bus, and like a peer to the networking stack in the operating system. With a special cable, you can setup a PAN between two computers.

So if one or more computers don't have an Ethernet or WiFi adapter, you can setup a physical network conveniently. But you will still have to define the logical network between the two computers. Setting up an IP based network, to share files between 2 computers, requires a significant amount of effort. That's in addition to loading the drivers to support the PAN itself. And there's no absolute guarantee that any PAN driver will work, between any 2 computers.

Ethernet and WiFi, on the other hand, are de facto standards for networking computers. They are designed for long term connection of computers. And there are a lot of people who know how to install, configure, and support Ethernet and WiFi.

And what if you have another device connected to the PAN bus on your computer? If you have a USB keyboard / mouse, and you're using a USB based network to connect to the Internet, your Internet access will have to share activity with your typing and cursor movement. The Ethernet bus was designed for inter computer connections, and is dedicated to that purpose.

In short, if you have an emergency, and can't open up your computer to install an Ethernet adapter, AND both computers in question have Firewire or USB ports, AND you have a Firewire or USB networking hub / cable, using Firewire or USB is a good short term solution. But in the long run, using Ethernet or WiFi to connect your computers makes more sense.

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Driver Updates From Microsoft? Please Pass.

To have a stable and secure system, you need to keep your software current. This includes downloading and updating both Microsoft, and third party, software.

Microsoft provides the Windows Update, and Automatic Update, facilities. On a monthly basis (or sometimes more often), Microsoft will issue recommended updates to the Operating System, to Microsoft applications, and even to third party drivers which may be relevant to your computer.

Whether you enable Automatic Updates, or retain control and monitor recommendations by Windows Update, is not the question here. Both have their advantages. But please, whatever you do, don't routinely download third party drivers from Microsoft.

Any time that you install a new computer accessory, consider the possibility that a firmware upgrade, for your product, was applied to units in the product line after your unit was packaged at the factory. The vendors aren't going to open each box, containing a given product, to apply a firmware upgrade. You have to do this yourself. So make it a consistent practice.

This is especially a relevant practice if one of the computers in your network is running Windows Vista. Right now, Windows Vista is subject to change; the drivers developed for Vista are, likewise, subject to change. Every change in Vista (and there have been a lot of changes since it was officially RTM) may affect a driver already released. Always check for new Vista drivers.

If there is a third party driver update that's relevant to your system, get it directly from the vendor, or from the manufacturer of the chip itself - that's what Microsoft does. Sometimes, what Microsoft may have available thru Windows Update is out of date, or is simply defective. You can get anything that's available directly from the manufacturer or the vendor, whenever you need it. If you need help locating the appropriate website, use Google, or websites like Network-Drivers.com.

But, whether you get updates from the vendor of the packaged product (whoever sold the computer to you), or from the manufacturer of the individual chip itself (who built the chip that needs the driver update), be selective about what you install.

• Find the manufacturer / vendor website.
• Read the documentation about the updates that are available, and decide whether what they offer will help you, with your specific problem.
• Download what they're offering, if you decide that you need it.
• Install the update, selectively removing the crap that you don't need.

Note that you need to be selective, when installing (or not) any driver update.

• Unless you see a security warning regarding your product in question, or you see mention of a specific problem that you're experiencing, be selective in what updates you apply. Don't waste time trying to fix what isn't broken.
• Any vendor of a consumer product probably bundles "extra offers" to "increase the consumer value" of what you install. Extra software, maybe trial offers of security products, is routinely added to many driver packages. Don't waste time applying software that you don't need.

Use Windows Update to keep your computer up to date with Microsoft products, but take its driver update notices simply as reminders. Then, if appropriate, follow the reminder, and get updates from the manufacturer or vendor, selectively choosing what you're offered.

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Networking Your Computers

Setting up a computer network, whether to share files, or Internet service, can be a lot of fun. It's more fun, though, if you set it up properly, from the start. I'll try and make that possible, if you work with me.

• Learn about the OSI Network Model.
  
  
• Learn basic networking skills
  • Linksys: Home Networking Basics.
  • Microsoft: (KB813936): How to set up a small network ...
  
  
  
• Learn basic terminology.
  • Microsoft: Glossary of Acronyms for PC and Server Technologies
  • PChuck: Physical Network Components Terminology.
  • PChuck: Windows Networking Terminology.
  
  
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• Design and setup the physical network.
  
  
  
  • I highly recommend, in all cases,
    
    
    
    • Use a LAN (Ethernet, FiberOptic Cable, or WiFi), for any permanent networking needs. Use a PAN (Firewire or USB), for any short term emergency needs. And understand the difference between the two.
    
    
    • If your Internet service is by broadband, a broadband (NAT) router is, by far, a good choice.
    
    
    • If you're setting up a WiFi network, know how to Setup WiFi Effectively.
    
    
    • If you're connecting two or more LANs thru the Internet, use a properly planned and designed Virtual Private Network.
      
  
  
  • I recommend, in most cases,
    
    
    
    • Use Ethernet, not WiFi, for the majority of your network.
    
    
    • Buy premade and tested, Ethernet cables.
    
    
    • Buy a router, whether you have one computer, two computers, or a household of computers.
    
    
  
  
  • I suggest, in specific cases,
    
    
    
    • Consider one specific code and safety issue, where FiberOptic Cable, or WiFi, would be preferred over Ethernet.
    
    
    • Read about installing electrical cable inside your home.
    
    
    • If you are connecting a NAT router between a broadband modem and a previously connected computer, know how to set the modem to recognise the router.
    
    
    • If you have 2 or more computers, you can connect them without using a router / wireless access point, using an ad-hoc network. With Ethernet cards on the computers, the simplest network you can setup is by directly connecting two computers with a cross-over cable; with WiFi adapters, you can setup an ad-hoc WiFi network. Know when and how to use a crossover cable, or how to setup an ad-hoc WiFi network, to connect your computers.
    
    
    • If you have your computers, connected by an ad-hoc network, and you wish to enjoy Internet service on each, one solution is to connect one directly to your Internet service, run ICS on it, and the others will have service too. Know when and how to use ICS to share Internet service.
    
    
    • If your Internet service is by dial-up, you can still protect yourself, and share service, with a dial-up compatible NAT router.
    
    
  
  


• Having completed the physical setup, test physical connectivity.


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• Design and setup the logical network.
  
  
  
  • I highly recommend, in all cases,
    
    
    
    • Read and understand the issues of Windows Networking.
    
    
    
    
  • I recommend, in most cases,
    
    
    
    • On a computer running Windows XP, run the Network Setup Wizard on each computer (as neccessary), and enable NetBIOS Over TCP (NetBT), the Microsoft supported networking transport, for file sharing, except for specific conditions.
    
    
    • On a computer running Windows Vista, run the Networking and Sharing Center wizard, and set the Network Location Type to Private.
    
    
  
  
  • I suggest, in specific cases,
    
    
    
    • If your LAN uses just one router, you have a simple broadcast domain, and file sharing should work right out of the box. If your LAN has to use two or more routers, you need to read about File Sharing On A LAN With Two Routers.
    
    
    • If you have two computers, each with its own Internet service, and pay for 2 IP addresses from your ISP, and want to run file sharing also, please disable NBT and use IPX/SPX for file sharing.
    
    
    • There may be legitimate reasons for using IPX/SPX or NetBEUI for file sharing. Know the advantages and disadvantages of using an alternate transport for file sharing.
    
    
    • Be aware of complications that you may experience when connecting different computers or routers directly to your broadband modem.
    
    
  
  


• Having completed the logical setup, test logical connectivity.


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• Design and setup the applications and security.
  
  
  
  • I highly recommend, in all cases,
    
    
    
    • Understand the differences between the various versions of Windows Vista and XP, and between Windows Vista / XP and other versions of Windows.
      • If you haven't purchased your Windows operating system yet, know about the different editions of Windows XP, and of Windows Vista, and choose the right one.
      • If you are setting up a network, with the operating systems already in place, understand the differences when setting up file sharing between each computer running Windows Vista / XP.
      • Know the issues when networking computers running Windows Vista / XP and older operating systems on the same LAN.
    
    
    • Even if you have just one computer, or especially if you have more than one computer, please Layer Your Defenses.
    
    
    • If you're setting up a WiFi network, know how to Setup WiFi Securely.
    
    
  
  
  • I recommend, in most cases,
    
    
    
    • If you have more than a couple computers, at least consider setting up a domain.
    
    
  
  
  • I suggest, in many cases,
    
    
    
    • If you're setting up a LAN to share a printer, be aware of the complexities of printer sharing, in addition to file sharing.
    
    
  
  


• Having completed the application and security setup, test Windows Networking connectivity.

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With the basic issues out of the way, you can get detailed instruction from plenty of websites, that will give you illustrated instructions. Here are but five, listed in alphabetical order.

• CableSense


• HomeNetHelp


• Microsoft Home Network Guide


• PracticallyNetworked


• Windows Networking

If you have properly chosen and setup your equipment, advice from any one of the above should get your network in order. The various guides are written by different organisations, and each has a different style, so check them all out if possible. Find the one which works best for you.

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Solving Problems
If you're here because you have problems, please start by reading Solving Network Problems.

Now, what is your specific problem? Is it accessing the Internet? Then read Troubleshooting Internet Connectivity. Or is the problem with File Sharing? Then read Troubleshooting Network Neighborhood (Windows Networking).

One major issue that the websites listed above won't help you with, if your problem is with file sharing, is the browser. Now when I mention the browser, don't start with "My Internet access is not a problem". The browser is the program that provides the contents of Network Neighborhood on your LAN. It's frequently involved in problems when "I can't see the other computers", or "I get access denied when I try to access another computer". Please read my article Windows NT (NT/2000/XP/2003) and the Browser.

Do you have a LAN with both Windows 9x (95, 98, ME) computers and Windows NT (NT, 2000, XP) computers? Then you should read Windows 9x (95/98/ME) and the Browser.

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In Conclusion
All of the above articles link to dozens of other articles, so read carefully. And be patient with me, as I add to this blog occasionally. Check back here periodically. Or write to my Guestbook.

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Does Your Computer Lose Network Connectivity When Not In Use?

Are you tired of turning your computer off and on again, after you let it sit for a while, unused, just to restore network connectivity?

Check Power Management settings, in the Network Adapter Settings wizard, which is accessible from the Connection Properties wizard.

On the Power Management tab, look at "Allow the computer to turn this device off to save power". Is that checked? If so, uncheck it.

If the above solution doesn't work, or isn't applicable, diagnose the problem a bit. When this happens again, open a command window, and type two commands, one after the other:

ipconfig /release
ipconfig /renew

Observing whether or not this helps can be a useful step in diagnosing the problem.

Dealing With Physical Network Problems

Network connectivity issues can easily be caused by physical network problems. Always ensure that you have a reliable and working connection between each computer and another, or each computer and a router.

Diagnosing a possible problem with a wired connection requires checking 3 components.

• The network card on this computer.
  
• The network cable.
  
• The network card on the other computer, or the router port.
  

Does your computer connect to another computer or to a router? If to a router, try another port on the router - preferably swap ports with another, working computer. Also, swap network cables with another computer. Always test with currently known good components, when possible. And please, always start with a pre-made network cable - this is NOT the time to try making your own Ethernet cable!

Remember that the network card on this computer, and the network card on the other computer (or the router) are all computers in their own right. Each device uses drivers and / or firmware. Check with the vendor, and see if this is a known problem, and / or is there a driver or firmware update available? Whenever you have a problem, start with updated software. If you ever go the vendor for advice, that is the first thing they will ask you about.

Examine the network card, or read the manual. Make sure that it doesn't contain an embedded hardware firewall, like the nVidia nForce.

Also, look at whether the problem is constant and permanent, or chronic. If chronic, is there a pattern to when it occurs, and / or is there a consistent workaround? One common example of this possibility would be loss of connectivity when the computer is idle for an hour or so.

Read Practically Networked Problems with Network Cards for suggestions on dealing with problems that originate with a network card itself.

Run the Device Manager (System Properties - Hardware tab), find the network adapter in question, and Troubleshoot it. See if the system can identify a hardware problem.

Always use the right kind of network cable, and always have a spare on hand. If you are connecting a computer to a router, you'll probably use a straight-thru aka patch cable. If you are connecting two computers directly, you will probably need a cross-over aka null-modem cable. Some newer network cards may support use of a straight-thru cable, to connect directly to another computer. But always have a spare cross-over cable to diagnose this problem.

Does the network card, and maybe the router port, have one or two colored lights that light up or change color? Observing their behaviour, and checking the owners manual, could save you a trip to your nearby computer store to buy the wrong component.

On most network cards, the Green light indicates Link (connectivity), while the Yellow light indicates Transmission (activity). The Green light should be solid, while the Yellow light may be either blinking (light activity), or solid (heavy activity).

Windows XP has the Local Area Connection status indicator in the tooltray. Windows Vista has the Network System Icon. Both will indicate logical network status, in some detail, if enabled (Local Area Connection Properties "Show icon ...").

If a router is the other end of the connection, try checking the router access log too. Having a second computer is very useful here.

If your network includes WiFi components, your issues may be even more complex to diagnose.

• WiFi operates at Layer 2 of the OSI Network Model, but it has its own network setup procedures.
  
• Besides networking, WiFi involves radio (really). The WiFi radio signal won't be uniformly available in your work area; however, it will leak into your neighbours work area (and your neighbours signal into your area).
  
• You can control your own network, but you cannot control your neighbours network. And your neighbours network use will affect your network.
  
• You must protect your network from your neighbour's use of it, intentional or not.
  

... or maybe not. If you have no connectivity at all, check that the radios on the computer and on the router / AP are powered on. Seriously.

For more information about WiFi, see Microsoft: A Support Guide for Wireless Diagnostics and Troubleshooting.

And in some cases, if you have XP SP2 on the computer, the (KB893357): WPA2 / WPS IE update for XP SP2 may help.

For truly unacceptable problems, prepare to uninstall the drivers for one or more network adapters.

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