Infrastructure Troubleshooting


No doubt, you will find yourself troubleshooting wiring and infrastructure problems less frequently than you'll troubleshoot client connectivity problemsand thankfully so. Wiring- and infrastructure-related problems can be very difficult to trace, and sometimes a very costly solution is needed to remedy the situation. When troubleshooting these problems, a methodical approach is likely to pay off.

A network infrastructure refers to the physical components that are used to create the network. This includes the media used, switches, routers, bridges, patch panels, hubs and so on.

When troubleshooting the infrastructure it is important to know where these devices are on the network and what they are designed to do. In this section we explore two essential infrastructure components, media and hardware components.

Troubleshooting Network Media

The physical connections used to create the networks are sometimes at the root of a network connectivity error. Troubleshooting wiring involves knowing what wiring your network uses and where it is being used. When troubleshooting network media consider:

Media range (attenuation) All cables used in networking have certain limitations, in terms of distance. It might be that the network problems are a result of trying to use a cable in an environment or a way for which it was not designed. For example, you might find that a network is connecting two workstations that are 130 meters apart with Category 5 UTP cabling. Category 5 UTP is specified for distances up to 100 meters, so exceeding the maximum cable length can be a potential cause of the problem. The first step in determining the allowable cable distance is to identify the type of cable used. Determining the cable type is often as easy as reading the cable. The cable should be stamped with its typewhether it is, for example, UTP Category 5, RG-58, or something else. Refer to Chapter 2 for more information on network media characteristics.

EMI and crosstalk interference Copper-based media is subject to the effects of EMI and crosstalk interference. UTP cables are particularly susceptible to EMI caused by devices such as power lines, electric motors, fluorescent lighting and so on. Consider using plenum rated cable in environments where cables are run through areas where EMI may occur. This includes heating ducts, elevator shafts and through ceilings around lighting fixtures. Crosstalk occurs when cables are run in close proximity and the signals from one interfere with the signals on the other. This can be hard to troubleshoot and isolate, so when designing a network ensure that crosstalk preventative measures are taken.

Throughout limitations A problem with a particular media may be simply that it cannot accommodate the throughout required by the network. This would create network-wide bottlenecks. It may be necessary to update the network media to correct the problem, for instance, upgrading the network backbone to fiber optic media.

Media connectors Troubleshooting media requires verifying that the connectors are correctly attached. In the case of UTP or coaxial, sometimes it may be necessary to swap out a cable with a known working one to test. For fiber, different types of connectors are used in fiber optic cabling. Before implementing a fiber solution, ensure that the switches and routers used match with the connectors used with the fiber optic cable.

For more information on cabling characteristics and connectors, refer to Chapter 2 "Cabling and Connectors."

Before running a particular type of media, place identification tags at both ends of each cable, which will be helpful while troubleshooting a failed cable.


Troubleshooting Infrastructure Hardware

If you are looking for a challenge, troubleshooting hardware infrastructure problems is for you. It is often not an easy task and usually involves many processes, including baselining and performance monitoring. One of the keys to identifying the failure of a hardware network device is to know what devices are used on a particular network and what each device is designed to do. Some of the common hardware components used in a network infrastructure are shown in Table 11.1.

Table 11.1. Common network hardware components, their function and troubleshooting strategies.

Networking Device Signs

Function

Troubleshooting and Failure

Hubs

Hubs are used with a star network topology and UTP cable to connect multiple systems to a centralized physical device.

Because hubs connect multiple network devices, if many devices are unable to access the network, the hub may have failed. When a hub fails,all devices connected to it will be unavailable to access the network. Additionally, hubs use broadcasts and forward data to all the connected ports increasing network traffic. When network traffic is high and the network is operating slowly, it may be necessary to replace slow hubs.

Switches

Like hubs, switches are used with a star topology to create a central connectivity device.

The inability of several network devices to access the network may indicate a failed switch. If the switch fails, all devices connected to the switch will be unable to access the network. Switches forward data only to the intended recipient allowing them to better manage data than hubs.

Routers

Routers are used to separate broadcast domains and to connect different networks.

If a router fails, network clients will be unable to access remote networks connected by the router. For example, if clients access a remote office through a network router and the router fails, the remote office would be unavailable. Testing router connectivity can be done using utilities such as ping and tracert.

Bridges

Bridges are commonly used to connect network segments within the same network. Bridges manage the flow of traffect between these network segments.

A failed bridge would prevent the flow of traffic between network segments. If communication between network segments has failed, it may be due to a failed bridge.

Wireless Access Points

Wireless access points provide the bridge between the wired and wireless network.

If wireless clients are unable to access the wired network, the WAP may have failed. However, there are many configuration settings to verify first.


For more information on network hardware devices and their function, refer to Chapter 3 "Network Devices."

Troubleshooting a Wireless Infrastructure

Wireless networks do not require physical cable to connect computers; rather, they use wireless media. The benefits of such a configuration are clearusers have remote access to files and resources without the need for physical connections. Wireless networking eliminates cable faults and cable breaks. It does, however, introduce its own considerations such as signal interference and security.

Wireless Signal Quality

Because wireless signals travel through the atmosphere, they are subjected to environmental factors that can weaken data signals. Everything from electrical devices, storms, RF interference, and obstacles such as trees can weaken wireless data signals. Just how weakened the signal becomes depends on many factors; however, all of these elements serve to decrease the power of the wireless signal.

Wireless signals degrade depending on the construction material used. Signals passing through concrete and steel are particularly weakened.


If you are troubleshooting a wireless connection that has a particularly weak signal, there are a few infrastructure changes that can be done to help increase the power of a signal.

  • Antenna Perhaps the first and most obvious thing to check is to ensure that the antenna on the wireless access point is positioned for best reception; this will often take a little trial and error to get the placement right. Today's wireless access cards commonly ship with diagnostic software that displays signal strength.

  • Device Placement One of the factors that can degrade wireless signals is RF interference. Because of this, it is important to try and keep wireless devices away from appliances that output RF noise. This includes devices such as microwaves, certain cordless devices using the same frequency, and electrical devices.

  • Network Location Although there might be limited choice, as much as possible, it is important to try to reduce the number of obstructions that the signal must pass through. Every obstacle strips a little more power from the signal. The type of material a signal must pass through also can have a significant impact on the signal integrity.

  • Boost Signal If all else fails, it is possible to purchase devices such as wireless repeaters that can amplify the wireless signal. The device takes the signal and amplifies it so that the signal has greater strength. This will also increase the distance that the client system can be placed from the WAP.

In order to successfully manage the wireless signals, you will need to know the wireless standard that you are using. The standards that are used today specify range distances, RF ranges, and speeds. It might be that the wireless standard is not capable of doing what you need. Table 11.2 highlights the characteristics of common wireless standards.

Table 11.2. Comparing Wireless Standards

Standard

Speed

Range

Frequency

Concerns

802.11a

Up to 54Mbps

2575 feet

5GHz

Not compatible with 802.11g or 802.11b

802.11b

Up to 11Mbps

Up to 150 feet

2.4GHz

Might conflict with other devices using the 2.4GHz range

802.11g

Up to 54Mbps

Up to 150 feet

2.4GHz

Might conflict with other devices using the 2.4GHz range

Bluetooth

720Kbps

33 feet

2.4GHz

Might conflict with other devices using the 2.4GHz range


As you can see in Table 11.2, the speeds are listed with the "Up to" disclaimer. This is because each standard will decrease the data rate if there is interference. 802.11b wireless link offers speeds up to 11Mbps, but it will automatically back down from 11Mbps to 5.5, 2, and 1Mbps when the radio signal is weak or when interference is detected. 802.11g auto sensing rates are 1, 2, 5.5, 6, 9, 12, 18, 24, 36, 48, and 54 Mbps. Finally, 802.11a provides rates up to 54Mbps, but will automatically back down to rates 48, 36, 24, 18, 12, 9, and 6Mbps.

Be prepared to answer questions on the specific characteristics of wireless standards on the Network+ exam.


Wireless Channels

RF channels are important parts of wireless communications. A channel is the frequency band used for the wireless communication. Each standard specifies the channels that can be used. The 802.11a standards specifies radio frequencies ranging between 5.15 and 5.875GHz. In contrast, 802.11b and 802.11g standards operate between the 2.4 to 2.497GHz range. As far as channels are concerned, 802.11a has a wider frequency band, allowing more channels and therefore more data throughput. As a result of the wider band, 802.11a supports up to eight nonoverlapping channels. 802.11b/g standards use the smaller band and support only up to three nonoverlapping channels.

It is recommended that the nonoverlapping channels be used for communication. In the United States, 802.11b/g uses 11 channels for data communication as mentionedthree of these, channels 1, 6, and 11, are nonoverlapping channels. Most manufacturers set their default channel to one of the nonoverlapping channels to avoid transmission conflicts. With wireless devices, you have the option of selecting which channel your WLAN operates on in order to avoid interference from other wireless devices that operate in the 2.4GHz frequency range.

When troubleshooting a wireless network, be aware that overlapping channels can disrupt the wireless communications. For example, in many environments, APs are inadvertently placed closely together. Perhaps two access points in separate offices are located next door to each other or between floors. Signal disruption will result if there is channel overlap between the access points. The solution here is to try and move the access point to avoid the problem with the overlap or change channels to one of the other nonoverlapping channels. For example, switch from channel 6 to channel 11.

As far as troubleshooting is concerned, you would typically only change the channel of a wireless device if there is a channel overlap with another device. If a channel must be changed, it must be changed to another nonoverlapping channel.

SSIDs

The Service Set Identifier (SSID) is a configurable client identification that allows clients to communicate to a particular base station. In application, only clients that are configured with the same SSID can communicate with base stations having the same SSID. SSID provides a simple password arrangement between base stations and clients.

As far as troubleshooting is concerned, if a client is not able to access a base station, ensure that both are using the same SSID. Incompatible SSIDs are sometimes found when clients move computers, such as laptops, between different wireless networks. They obtain an SSID from one network and then if the system is not rebooted, the old SSID won't allow communication to a different base station.

WEP Settings

The Wired Equivalent Privacy (WEP) is a security protocol for wireless networks that encrypts transmitted data . WEP is easy to configure with only three possible security optionsOff (no security), 64-bit (basic security), and 128-bit (stronger security). WEP is not difficult to crack, and using it reduces performance slightly.

If your network operates with WEP turned off, your system is very open for someone to access your data. Depending on the sensitivity of your data, you can choose between the 64-bit and 128-bit encryption. Although the 128-bit WEP encryption provides greater security, it does so at a performance cost. 64-bit offers less impact on system performance and less security.

As far as troubleshooting is concerned, in order for wireless communication to take place, wireless devices must all use the same WEP setting. Most devices are set to Off by default; if changed, all clients must use the same settings.

Wireless AP Coverage

Like any other network media, APs have a limited transmission distance. This limitation is an important consideration when deciding where an AP should be placed on the network. When troubleshooting a wireless network, pay close attention to the distance that client systems are away from the AP.

When faced with a problem in which client systems cannot consistently access the AP, you could try moving the AP to better cover the area, but then you might disrupt access for users in other areas. So what can be done to troubleshoot AP coverage?

Depending on the network environment, the quick solution might be to throw money at the solution and purchase another access point, cabling, and other hardware, and expand the transmission area through increased hardware. However, there are a few things to try before installing another wireless access point. The following list starts with the least expensive solution to the most expensive.

  • Increase transmission power Some access points have a setting to adjust the transmission power output. By default, most of these settings will be set to the maximum output; however, it is worth verifying just in case. As a side note, the transmission power can be decreased if trying to reduce the dispersion of radio waves beyond the immediate network. Increasing the power would provide clients stronger data signals and greater transmission distances.

  • Relocate the AP When wireless client systems suffer from connectivity problems, the solution might be as simple as relocating the WAP to another location. It might be that it is relocated across the room, a few feet, or across the hall. Finding the right location will likely take a little trial and error.

  • Adjust or replace antennas If the access point distance is not sufficient for some network clients, it might be necessary to replace the default antenna used with both the AP and the client with higher end antennas. Upgrading an antenna can make a big difference in terms of transmission range. Unfortunately, not all WAPs have replaceable antennas.

  • Signal amplification RF amplifiers add significant distance to wireless signals. An RF amplifier increases the strength and readability of the data transmission. The amplifier provides improvement of both the received and transmitted signals, resulting in an increase in wireless network performance.

  • Use a repeater Before installing a new AP, you might want to first think about a wireless repeater. When set to the same channel as the AP, the repeater will take the transmission and repeat it. So, the WAP transmission gets to the repeater, and then the repeater duplicates the signal and passes it forward. It is an effective strategy to increase wireless transmission distances.



    Network+ Exam Cram 2
    Network+ Exam Cram 2
    ISBN: 078974905X
    EAN: N/A
    Year: 2003
    Pages: 194

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