Document the solution

Like the comprehensive testing step of the strategy, this step is likely to be done poorly or not at all – after all, the problem has been fixed. However, this step may be the most important. Not only will complete documentation be invaluable the next time a problem such as this occurs, but it will also record the changes made and how to revise them if the solution does end up affecting network performance.

If external help was required, the documentation should be completed so that this help can be easily enlisted again in the case of a similar problem. Details such as telephone

numbers, email addresses and web sites used should be recorded.

Rather than file the documentation under date (although this information is useful), it should be categorised and stored accordingly. If the documentation is stored on an online database, it should follow a defined standard, as should a paper-based system, with the network administrator completing certain information that will assist in the easy retrieval of the document at a later date, if required.

Troubleshooting problems in different topologies

Bus

The most common bus topology implementation is Ethernet using coaxial cable with termination at both ends. Most problems occur due to poor cable installation and incorrect termination.

To work properly, each end of the bus must be properly terminated with a connector of the appropriate resistance; one of the ends must also be grounded. The end connector is used to absorb signals that reach the end of the bus, if the resistance is incorrect, signal bounce may occur with the signal travelling back down the wire and causing interference. If both ends are grounded, this may cause a ground loop, which can also adversely affect the network.

Star/hierarchical

The star topology is most common network topology used today ranging from small SOHO (small office or home office) networks to large enterprise networks. The star topology scales well and is generally more cost-effective to set up and run than the other topologies. All that is required in a simple star topology is some machines with NICs connected by cable to a central hub or switch.

The strength of a star topology, that of a central hub, is also its main weakness. If this central device is faulty, the whole network will fail. However, if a workstation attached to the hub fails, this will have no effect on the other devices on the network and the network will perform as usual.

Mesh

In a mesh topology, every device is connected to every other device. A mesh is a very robust topology with a lot of redundancy; however, it is rarely found in the form of a LAN and is more likely to be found in a WAN implementation.

The problems beset by the other topologies would not typically affect the mesh because of its in-built redundant links, therefore, if there was a cable break the network would still continue to function. Any problem with a mesh topology would tend to be very serious with a complete centre or node down.

Ring

All of the devices on a ring topology are dependant on each other. A common ring implementation is token ring, where a token is passed around the network from device to device to allow communication. However, the problem with this is that if a workstation is faulty it may not be able to pass the ‘token’; therefore the whole network will be down, as no-one has the required token to be able to transmit. This is in a contrast to the star where it would not matter if a workstation is not working.

Network Concepts: Advanced COLEG

The other problem with the ring is the cabling. If the cabling is damaged, the network will fail. One solution to this is to have two rings operating simultaneously but with the token travelling in the opposite direction in each.

Wireless

The cabling problems found in all of the other topologies do not exist in the wireless

topology, but that is not to say that this topology is without its connectivity problems. These problems are generally due to protocol issues and signal interference.

The two popular wireless protocols in use are Bluetooth and 802.11. These protocols do not work together and as such a device using Bluetooth will not be able to connect to an 802.11 network and vice versa.

Signal interference and signal loss in a wireless topology come about due to other products that operate at the same frequency as the network. This includes items such as cordless phones and microwave ovens. Signal loss can occur due to a user being too far away from a wireless access point (AP).

Troubleshooting SOHO network failure

The growth of SOHO (small office/home office) workers goes hand in hand with the advent of high-speed connections to the Internet and to organisation’s internal networks. The technologies embraced by the SOHO movement include digital cable and DSL services.

The rise in use of these technologies has brought many benefits, not the least being the cost savings of having SOHO workers; however, it has also brought new challenges for the network administrator, who prior to this was in control of a network within a single location, usually the same building. Now the network administrator has to deal with external clients to the company LAN. This makes troubleshooting network problems more problematic.

There are many ways that a network administrator can allow remote connectivity to the company LAN:

• Remote node: This works by viewing the SOHO machine as being just a normal machine with the dial-up being just another network cable. A SOHO worker will then be able to log in as normal as if they were at a terminal within the company.

• Remote control: This works by using a remote control (host) machine within the company LAN, which is remotely controlled by the SOHO machine. Any work carried out by the user is sent to the host machine where all of the processing is carried out. The home machine is only really being used for input and output purposes.

• SSH (Secure SHell): This is a program that allows the remote logging in to a remote machine. The connection is safe and secure and allows the user to issue encrypted commands to the remote system, although this is invisible to the user.

The functionality is similar to that of TELNET, but with complete security.

• VPNs: This is a popular and secure method of using the Internet to connect to a remote computer. VPN hardware and software are used to create a secure pipeline between the SOHO computer and the company LAN using encryption. The user will login to the remote system as normal and be able to use their home office PC as they would a PC within the company.

Troubleshooting SOHO xDSL

Many SOHO users are now turning to broadband digital technology for remote access.

The term broadband implies the use of one cable that can handle many signals, as opposed to baseband, where only one signal can travel on the single line. The rise of broadband has led to homes using cable not only for computing purposes but also for television through cable.

One broadband technology, DSL, offers high-speed digital connection using pre-existing copper telephone wires. The speed difference can be up to 35 times faster than a normal dial-up connection. Because they are broadband, DSL services are ‘always on’, which eliminates the connection problems experienced by dial-up users.

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The DSL technology is commonly referred to as xDSL because there are variations on the type of service and system. The most common xDSL technologies are:

• Asymmetric Digital Subscriber Line (ADSL)

• Symmetric Digital Subscriber Line (SDSL)

• Adaptive Rate Digital Subscriber Line (aRDSL)

• ISDN Digital Subscriber Line (IDSL)

The drawback to DSL provision is distance from the user to their local telephone exchange. The nearer the user is, the more likely it is that they will have DSL services available to them. Typically, if the user is more than approximately 5 kilometres away from the exchange, their DSL options are limited. For the users who are within this limitation they can make use of high-speed DSL services by using the normal copper telephone wire without need for any other connection media.

When a problem occurs with DSL is it not usually at the user’s side. However, there are a few things that can be checked before the network administrator gets in touch with the DSL provider:

• Is the DSL router switched on? This may seem like common sense but it pays never to overlook the obvious, especially if the network administrator is going to contact the DSL provider. This may be the first question they ask.

• Are all the correct LEDs on? These will vary between DSL devices, but there should be a WAN and LAN light. The WAN link light should stay on permanently. If this light is off or blinking then there is a problem with the DSL loop.

• Is the router correctly connected to the SOHO PC? The DSL router should be connected by a cable from its Ethernet port to the PCs, NIC or hub. The link lights on the router and on the local device should be on; if they are not, the problem is usually the patch cable used to connect the devices. The network administrator should try changing the cable or the port on the hub the cable is going into.

• Does pinging a remote link work? The network administrator will start by pinging the Ethernet port of the DSL router, then the default gateway, and finally an

address on the Internet. The point at where the ping fails will help determine where the problem lies.

Troubleshooting SOHO cable

The main difference between cable and DSL broadband technologies is that with cable the data travels over a shared loop, which means that transfer rates drop as more users access the resource. However, the connection performance is not only limited by the number of users, but what these users are doing that may affect the data transfer rates.

As far as the network administrator is concerned, the main problem with cable is with regards to security in what is basically a shared medium, e.g. the SOHO user’s LAN may be peer-to-peer, which means that a shared printer on one device would be available to

any of the users using the shared cable. The local user must therefore make sure that the appropriate security measures are in place for high risk items.

Troubleshooting cable is similar to troubleshooting DSL in that if there is a fault it will not usually be on the user’s side. Therefore, the same troubleshooting steps as before should be carried out. One possible difference is concerned with connection to the cable device.

In many cases this will be a one-to-one connection from the cable device to PC rather than from a cable box to a hub or a switch and then to the PC. In the case of a direct

connection, a further troubleshooting step should be to check the computer’s IP settings.

These settings may give an additional clue to what is wrong. The following are typical errors:

• IP address missing or set to 0.0.0.0. The network administrator should check the cables from the cable box to the PC and change if required. If this doesn’t work then the NIC and its drivers should be checked.

• IP address is in range 169.254.xxxx.xxxx. This is an APIPA (automatic private IP addressing) allocation and it means that the machine has failed to get an address from a DHCP server. This private address will let the user onto the local machine to work on it, but they will not be able to access the Internet or their company

network. The network administrator may be able to fix this by power cycling the systems, making sure that the cable router is turned on first.

• IP address is in the range 192.168.100.xxxx. This is an IP address allocated by the cable router’s inbuilt DHCP server. This allows the user to use the machine and indicates that the cable router is working but is not connecting to the cable provider. The network administrator will have to contact the cable provider.

Troubleshooting SOHO satellite Internet

In some cases, satellite Internet may be the only option a SOHO user has to get access to a high-speed digital connection. This technology does not need physical telephone lines or cables but rather needs a satellite dish for digital communication. Satellite is probably about 10 times faster than dial-up connections.

The network administrator must be aware that there may be problems getting the satellite system set up because professional installation is not available in all areas. With this in mind, the network administrator should take heed of manufacturer’s documentation and other advice regarding setup.

Once the system is set up and working, the problems that may arise are within the nature of the technology. As with satellite television, satellite Internet is vulnerable to adverse weather conditions and obstacles. The most common problem with satellite is dish placement and alignment. If the reflector is positioned properly, the SOHO user will get a strong signal; however, if it is not then the signal will be weakened. Adjusting the reflector can be aided with the use of satellite diagnostic software. This would primarily be a job for two people. One to make slight changes to the satellite reflector and the other to monitor the progress on computer.

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Troubleshooting SOHO wireless

The key differences between wire-based and wireless networks is the absence of the physical connection media and the methods used to access the media. Radio waves are used in place of the wires to allow network devices to communicate between each other.

There are many wireless standards available, however, the most common in SOHO environments are:

• IEEE 80211b Wi-Fi (Wireless Fidelity)

• Home Radio Frequency (HomeRF)

• Bluetooth Wireless

Generally, the problems for wireless will be exactly the same as that for wired networks.

Problems such as incorrectly configured network devices and software will still be present, e.g. TCP/IP settings, and can be solved as stated previously. Similarly, wireless hardware devices such as access points can be visually checked to make sure that the link lights are working and also that the interconnect cable are properly in place.

Other problems, specific to wireless networks, come in the form of distance limitations and signal interference. Users must be made aware of these limitations and know that they should stay within the defined area to avoid signal degradation. This would apply to wireless networks that utilise multi-access points as well as single access points.

Signal interference can be a problem because of the many normal elements in a SOHO environment that could interfere, such as electrical wires, lights, telephone lines and even kitchen appliances. Therefore, although wireless devices can work through walls, ceilings and floors the user has to realise that there may be hidden elements that could interfere with the network signal. As well as educating the user to this, the

network administrator may be able to solve some problems by the repositioning of the access point(s).

Troubleshooting PSTN or POTS

When troubleshooting for SOHO users the network administrator must keep in mind that not all connections will be high speed. There may be users that are still using dial-up connections over the telephone system, the derogatory term for which, as we have already seen is plain old telephone system (POTS). Initially, this was the most popular means of remote connection because all that was needed was a modem to connect to each end of the communications link and an operating system that supports dial-up connections, which all of the major ones do.

Generally dial-up systems using POTS are quite reliable; however, there may still be problems. The common problems areas are:

• Logon issues: login user name and password errors

• Hardware issues: the modem

• Software issues: the software drivers used

• Connection issues: the telephone line

Concerning the first item, it is widely recognised that many network problems can be resolved by the user logging on and logging off correctly. The network administrator must make sure that any network changes that could affect the remote user are communicated to them, e.g. a change of domains.

The second two issues should not arise if the modem is installed correctly in the first instance. Therefore, it is vital that when a modem is installed the correct drivers are used.

If it is feasible, the network administrator should check the modem manufacturer’s website to ensure that the latest drivers are downloaded.

If the local modem is installed correctly, other possible problems involve the company host modem. The network administrator must make sure that the host modem being dialled is available and answering. One way to check this is to use a normal telephone to dial into the host modem. If this is working, the network administrator should hear a high pitched sequence of modem noise. The next step is to see if the local modem is responding to the host modem on dial-up. This can be done through the use of software, such as

Hyperterminal, and the use of Hayes AT commands. These commands can be used to check if the local modem is working. The local machine’s COM port can be ruled out from the process if the other COM port is used. If this fails, a replacement modem can be used to eliminate the local modem as the point of failure.

Interference on telephone lines is another area where problems may occur. If a connection is made and the lines are unacceptably slow or there are line drops occurring, special line testers can be used to check the line. However, these tools are extremely expensive and as such the best option is to contact the telephone company and get their help.

One final issue to do with telephone lines is that they are at the mercy of intermittent, unforeseen events. These events include weather problems such as storms and extremely hot or cold weather.

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Troubleshooting remote connectivity problems

Remote access to the private company network is vital for today’s users who are constantly on the move. It is vital for the user who is mobile to have a guaranteed connection to the company network. If they do not then they cannot do their job.

Troubleshooting RAS

The key piece of equipment that must be maintained for remote access is a RAS (remote

The key piece of equipment that must be maintained for remote access is a RAS (remote