Network Troubleshooting
7.0 Network Troubleshooting
7.1 Definition
- Network
troubleshooting means recognizing
and diagnosing networking problems with
the goal of keeping your network running
optimally.
- As
a network administrator, your primary concern
is maintaining connectivity of all devices (a process often
called fault management).
- You
also continually evaluate and improve your network's performance.
- Because
serious networking problems can
sometimes begin as performance
problems, paying attention to performance can help you address issues before they become serious.
7.2
About Connectivity Problems
- Connectivity
problems occurred when end stations cannot communicate with
other areas of your local area network (LAN) or wide area network (WAN).
- Using
management tools, you can often fix a connectivity problem before users even
notice it.
- Connectivity
problems include:
·
Loss of
connectivity - When users
cannot access areas of your network, your organization's effectiveness is
impaired. Immediately correct any connectivity breaks.
·
Intermittent connectivity -
Although users have access to network resources some of the time, they are
still facing periods of downtime. Intermittent (on/off) connectivity problems can indicate that your network is on the verge of a major
break. If connectivity is erratic, investigate the problem immediately.
·
Timeout
problems - Timeouts
cause loss of connectivity, but are often associated with poor network
performance.
methodically and resolve it with minimal disruption(error) to network
users.
- It is also important to have an accurate
and detailed map of your current network environment.
- Beyond that, a good approach to problem
resolution is:
- You
may discover network problems in
several ways:
- Users may complain that the network seems slow or that they cannot connect to a server.
- You may pass your network management station and notice that a node icon is red.
- Your beeper may go off and display the message.
- User Comments
Although you can often solve
networking problems before users notice a change in their environment, you
invariably get feedback from your users about how the network is running, such
as:
b. Analyzing Symptoms
-When a symptom occurs, ask yourself these
types of questions to narrow the
location of the problem and to get
more data for analysis:
- To what degree is the network not acting normally (for example, does it now take one minute to perform a task that normally takes five seconds)?
- On what sub network is the user located?
- Is the user trying to reach a server, end station, or printer on the same sub network or on a different sub network?
- Are many users complaining that the network is operating slowly or that a specific network application is operating slowly?
- Are many users reporting network logon failures?
- Are the problems intermittent? For example, some files may print with no problems, while other printing attempts generate error messages, make users lose their connections, and cause systems to freeze.
c. Understanding the Problem
-When
communication becomes problematic, you must determine why data are not traveling as expected and then find a solution.
-The
two most common causes for data not moving reliably
from source to destination are:
- The physical connection breaks (that is, a cable is unplugged or broken).
- A network device is not working properly and cannot send or receive some or all data.
- The
test must conclusively prove or disprove your theory.
- For
example, with "LAN sentry Manager", you can set alarms and automatic packet capture filters to monitor your network and inform
you when the problem occurs again.
- Although
network management tools can provide a
great deal of information about problems and their general location, you may still need to swap equipment or replace components of your network until you
locate the exact trouble spot.
e. Sample Problem Analysis
- You
need to establish two areas of
information:
- What you know - In this case, the user's workstation cannot communicate with the mail server.
- What you do not know and need to test?
- Can the workstation communicate with the network at all, or is the problem limited to communication with the server? Test by sending a "Ping" or by connecting to other devices.
- Is the workstation the only device that is unable to communicate with the server, workstations?
- If other workstations cannot communicate with the server, can they communicate with other network devices? Again, test the connectivity.
- If
one solution does not work, continue with another.
o
Upgrading software
or hardware (for example, upgrading
to a new version of agent software or installing Gigabit Ethernet devices)
o
What users communicate with which servers?
Network
load
7.4 Common Physical Problems in Network
-When you experience network troubles, begin
by checking the physical network devices and connections.
- In my experience, about 25–30 percent of all networking
problems result from
problems with the physical network. These problems are also the most easily fixed.
-Make a thorough physical inspection of
your network.
o
Is the router plugged in?
o
Have you accidentally substituted a
cross-over cable for a regular network cable?
o
Are all the network cables in good condition
and well seated?
o
Has the dog been chewing on your network
cable?
- Microsoft Windows XP can help you see if a
network cable is unplugged. As shown in Figure 2, if your cable is completely
unplugged, this status appears in your Network Connections window. But a cable
that is damaged or partially removed may not appear as disconnected.
Figure
2 cable is completely unplugged
1. Cabling problems
- Check that your cable type is appropriate for the line speed you are using. For example, category 3 cable cannot be used for 100 Mbps.
- Is the cable wired correctly?
- Do all cables, patch cables, and patch panels the network, switch or hub support your line speed? For example, if the line speed is configured at 100 Mbps, the cable must be category 5 to support the speed.
2.
Connectivity Problem
A connectivity problem with
one or more devices in a network can occur after a change is made in
configuration or by a malfunction of a connectivity component, such as hub, a
router or a Switch.
3.
Excessive Network Collisions:
These often lead to slow connectivity. The problem can occur as a result of bad
network setup/plan, a user transferring a lot of information or jabbering
network card.
4.
Software Problem:
Network problems can often be traced to software configuration such as DNS
configuration, WINS configuration, the registry etc.
5.
Duplicate IP Addressing: A
common problem in many networking environments occurs when two machines try to
use the same IP address. This can result in intermittent communications.
- Following is a list of some common problems
that occur:
- Faulty RJ-45 - The network connection fails intermittently.
- Faulty wiring on patch cable - No network communications.
- mdi to mdi (no mdi-x) - Media data interfaces, such as hubs, are not connected to another mdi device. Many hubs have a port that can be switched to become an mdi-x mdi crossover port.
- Badly configured encryption - Once encryption is configured, things are not as they appear. Standard tools such as ifconfig, and netstat will not locate the problem. Use the snoop utility to view the contents of packets to determine if all is normal.
- Hub or switch configured to block the MAC - Modern hubs and switches are configured to block specific MAC addresses or any addresses if the connection is tampered with. Access to the console of the hub or switch is necessary to unblock a port.
- Bad routing tables or rogue router - Routing tables can be corrupted. Sometime a rogue router can appear of the network due to installation of multihomed host.
- Rogue DHCP server is present in DHCP environment. Often happens when somebody installs Windows server on the network without understanding what they are doing.
- Protocol not being routed - for example if jumpstart or bootp is being used across routers.
- Interface not plumbed - Additional interfaces, when configured, are not plumbed. The interface will appear to be functioning, but it will not pass traffic.
- Connection to the wrong interface on multihoned host.
- Bad information in the /etc/hosts or NIS database - The IP address of systems is incorrect or missing.
7.4.1 Troubleshooting software-interaction problems
-If the physical network is fine and your
basic configuration looks right, it's time to think about a software problem.
- The most common software problems are related to firewalls
- Many third-party antivirus programs, such
as Trend Micro's PCCillin or Norton AntiVirus, include built-in firewalls.
-You may not realize that you installed the firewall component when you installed
the antivirus software, and now that
firewall is getting in the way of connectivity on your home network.
- Network software, such as Ping, NSlookup, and Netstat and traceroute (tracert).
- Network monitoring devices, such as Analyzers and Probes.
- Tools, such as Cable Testers, for working on physical problems.
7.4.1 Trouble shooting using Ping command
a. Introduction
- Ping attempts to transmit
a packet from one device to a
station on the network, and listens
for the response to ensure that it was correctly received.
- You
can validate connections on the parts of your network by pinging different
devices:
- Some
network devices, like the Core Builder 5000, must be configured to be able to respond to Ping messages.
-
If you are not receiving responses from a
device, first make sure that it is set up to be a Ping
responder.
-
Strategies for using ping are ping devices
when your network is operating normally
so that you have a performance baseline
for comparison.
b. Strategy using Ping
command
2.
This method allows you to Ping your network segments in an organized
way, rather than having to remember
all the hostnames and locations.
3.
Ping your Domain Name System (DNS) if the server is down and your system cannot look up host
names properly.
6.
To troubleshoot problems that involve large
packet sizes, Ping the remote host repeatedly, increasing the packet size each time.
7.
To determine if a link is erratic, perform a continuous Ping
(using ping -s on UNIX), which indicates
the time that it takes the device to respond to each Ping.
8. Consider
creating a Ping script that periodically sends a Ping to all necessary networking devices.
9.
If a Ping failure message is received, the script can perform some action to notify you of the problem, such as paging
you.
10. Use
the Ping functions of your network management
platform. For example, in your HP OpenView map, select a device and click the
right mouse button to gain access to ping functions.
7.4.2
Trouble shooting using IPconfig
-ipconfig is
a command line utility available on
all versions of Microsoft Windows starting with Windows NT.
- ipconfig is designed to be
run from the Windows command prompt.
- This utility allows you to get the IP address information of a Windows
computer.
- Ipconfig can be used to display TCP/IP network configuration values, discard the current IP and
DHCP settings for a device, and renew the DHCP settings for a device.
- Below list a ipconfig
command:
- Ipconfig /? displays all the Ipconfig commands and the syntax of the program.
- Ipconfig /all displays the network settings for a TCP/IP device on the network, as you can see in figure.
- You can use this information to track the IP addresses assigned to computers on your network, and make sure that there is no conflict caused by two computers having been assigned the same address.
- Ipconfig /release send a message to the DHCP server to release the current IP address for a device on the network.
- Ipconfig /renew sends a message to the DHCP server to renew the IP address of your computer, provided your computer is set up to automatically obtain its IP address. The results of running this command on my computer are shown in figure.
- ipconfig /showclassid, ipconfig /setclassid - These options manage DHCP class identifiers. DHCP classes can be defined by administrators on a DHCP server to apply different network settings to different types of clients. This is an advanced feature of DHCP typically used in business networks, not home networks.
7.4.3
Trouble shooting using Traceroute (tracert)
-Traceroute is the program that shows you the route over the
network between two systems, listing all the intermediate routers a
connection must pass through to get to its destination.
- It can help you determine why your connections to a given server might be poor, and can often help you figure out where exactly the
problem is.
- It also shows you how systems are connected to each other, letting you see how your ISP connects to the Internet as well as how
the target system is connected.
-traceroute
also called diagnostic tool for displaying the route (path) and measuring transit delays
of packets across an Internet Protocol (IP) network.
- For example see line (7), myren.net.my is an ISP for psmza.
-How to Use TRACERT to
Troubleshoot
- -You can use TRACERT to find out where a packet stopped on the network.
- In the following example, the default gateway has found that there is no valid path for the host on 22.110.0.1.
- Probably, either the router has a
configuration problem, or the 22.110.0.0
network does not exist, reflecting a bad IP address.
- The command:
C:\>tracert
22.110.0.1
The output from the command:
Tracing route to 22.110.0.1 over a maximum of 30 hops
-----------------------------------------------------
1 157.54.48.1 reports: Destination net unreachable.
Trace complete.
-Traceroute utilities work
by sending packets with low time-to-live (TTL) fields or hop. - The TTL value specifies how many hops the packet is
allowed before it is returned.
- When a packet can't reach its destination because the
TTL value is too low, the last host
returns the packet and identifies itself.
- By sending a series of packets and incrementing the TTL value with each
successive packet, traceroute finds
out who all the intermediary hosts are.
7.4.4
Trouble shooting using Netstat
-
Netstat is a common command line TCP/IP networking utility available
in most versions of Windows, Linux, UNIX and other
operating systems.
- Netstat provides information and statistics about protocols in use and current TCP/IP network connections.
(The name derives from the words network
and statistics.)
- The Windows help screen (analogous to a
Linux or UNIX man page) for netstat
reads as follows:
- Displays protocol statistics and current
TCP/IP network connections.
-a (active connections
display),- to view and remove phantom connections.
-i (active interfaces display),
-to troubleshoot incoming and outgoing packet errors.
-m (streams allocation), -to
check on streams failures.
-r (routing tables),
-to verify the presence of needed routes.
-e Displays Ethernet statistics.
This may be combined with the -s option.
- Netstat
can be a helpful forensic tool when trying to determine what processes and
programs are active on a computer and involved in networked communications.
- It
can provide telltale signs of malware compromise
under some circumstances and is a good tool to use to observe what kinds of
communications are underway at any given time.
7.4.5
. Trouble shooting using NSlookup
- Nslookup is
a network administration command-line
tool available for many computer operating systems for querying the Domain Name
System (DNS) to obtain domain name
or IP address mapping or for any
other specific DNS record.
- The
name nslookup means name
server lookup.
- Nslookup
uses the operating system's local Domain
Name System resolver library to perform its queries.
- It
will also do reverse name lookup and
find the host name for an IP address you specify.
- For
example,
o
Go Run and type cmd
o
Type nslookup
o
Require for www.psmza.edu.my, its will show
default server, ip address, ip number (provide by ISP) as below.
- nslookup
sends a domain name query packet to
a designated (or defaulted) domain name system (DNS) server. Depending on the
system you are using, the default may be the local DNS name server at your
service provider, some intermediate name server, or the root server system for
the entire domain name system hierarchy.
- You
can also access NSLOOKUP online from the following websites.
- To use the Windows version of nslookup, open a
command prompt and launch the tool as follows:
C:\>
nslookup
Default Server: resolver1.opendns.com
Address: 208.67.222.222
\>
Default Server: resolver1.opendns.com
Address: 208.67.222.222
\>
- This first step identifies
which DNS server configured on the PC is in use for look-ups.
- By default, nslookup responds with the
primary IP address associated with a
domain specified. To query the primary address of about.com, for example:
C:\>
about.com
Address: 67.215.65.132
Address: 67.215.65.132
7.5
Hardware/Device to diagnosis problem on Network
a.
Network Analyzers
- An analyzer, which is
often called a Sniffer, is a
network device that collects network
data on the segment to which it is attached, a process called packet capturing.
- Software on the device analyzes this data, which is a process referred to as protocol analysis.
- Most analyzers can interpret different
types of protocol traffic, such as
TCP/IP, AppleTalk, and Banyan VINES traffic.
- You usually use analyzers for reactive troubleshooting.
- When you see a problem somewhere on your
network, you attach an analyzer to
capture and interpret the data from that area.
- Analyzers are particularly helpful for
identifying intermittent problems.
-For example, if your network backbone has
experienced moments of instability that prevent users from logging on to the network,
you can attach an analyzer to the backbone to capture the intermittent problems
when they happen again.
b.
Probes
- Like Analyzers,
a probe is a network device that collects network data. Depending on its type,
a probe can collect data from multiple segments simultaneously.
-It stores the collected
data and transfers the data to an analysis site when requested. - - - Unlike an
analyzer, probes do not interpret data.
- The
Transcend Enterprise Monitor 500 series and the SuperStack® II Monitor
series are stand-alone RMON probes.
Transcend Enterprise Monitor 500 series
SuperStack® II Monitor series
-
LANsentry Manager and Traffix Manager use data from probes that comply with
the "RMON MIB" or
the "RMON2 MIB".
LANsentry Manager
Stand-alone RMON probes
-
You can use a probe daily to determine the health of your network.
-
The Transcend NCS applications can interpret and report this data, alerting you
to possible problems so that you can proactively manage your network.
-
For example, an RMON2 probe can help you to analyze traffic patterns on your
network.
-
Use this data to make decisions about reconfiguring devices and end stations as
needed.
c.
Cable Testers
-
They are most commonly used to ensure that building wiring and cables meet
Category 5, 4, and 3 standards.
-
For example, network technologies such as Fast Ethernet require the cabling to
meet Category 5 requirements.
-
Testers are also used to find defective and broken wiring in a building.
Cable Testers
d.
LANScan Network Monitoring
and Diagnostic Software
-LANScan is a fast and easy to use
program for monitoring network activity.
-Fully compatible with Microsoft Windows XP,
2000 and ME/98, LANScan requires no special hardware to instantly see
into your network.
-Install LANScan on any PC on your
network and it will collect data automatically.
-Built in real time graphics and dynamic
lists display network activity in a way that is easily understood by all
users.
-Use LANScan to solve common network
problems including network slowdowns; device availability; inappropriate use;
application failures and more.
-LANScan identifies all network
devices and reports on their activity making it easy to identify unwanted or
unexpected users.
- LANScan Network Monitor is full of features
for monitoring your network, locating problems, analyzing performance and
managing usage.
e. Network Diagnostic Tool (NDT)
-The Network Diagnostic Tool
(NDT) is a client/server program that provides network configuration and
performance testing to users desktop or laptop computer.
- The system is composed of
a client program (command line or java applet) and a pair of server programs (a
webserver and a testing/analysis engine).
- Both command line and web-based clients
communicate with a Web100-enhanced server to perform these diagnostic
functions.
- Multi-level results allow novice and expert
users to view and understand the test results.
e. Monitor Network Latency with Enhanced Ping
- Continuously monitor servers, routers, workstations, or other devices and show real-time response rates
- View graphical results as ribbon charts, bar charts, column charts, step charts, or area charts
- Enhanced Ping can be used to continuously monitor a number of servers, routers, workstations, or other devices and continually show real-time response rates.
- Enhanced Ping has a robust graphing utility that allows you to view ping results in a ribbon chart, bar chart, column chart, step chart or area chart.
- Its provide the option of creating and saving a network latency profile of your network devices for future benchmarking.
- Network latency is plotted against packet loss, even tracking the network latency high/low limit recorded during the sample period.
More visit http://www.solarwinds.com/products/toolsets/EnhancedPing.aspx
7.6
Common faults in cabling
Cabling Faults
-
Many established networks contain a mixture
of old and new cables, but which are Cat 4, Cat 5, or Cat5e.
-
Sometimes when networks are upgraded older
patch cables are left in place.
-
Just because a cable was fine on the old
network does not mean it will work on the new upgraded network. It can be hard
to identify these faults without some kind of test kit.
-
Is the cable itself faulty? Checking the
pairs will identify faults.
Network Speed
-Something that reports
network speed is very useful.
- Link testing can be used
to identify the network speed. It’s useful to find out additional network
information using DHCP.
- If you are running Gigabit
on your network you need to ensure that you’re cabling is up to the Cat5e
standard, the older Cat5 standard is fine for 100M but needs careful checking
if you intend to run Gigabit. Many organizations only discover this too late.
Cable Length
-
The longer the cable the more the signal is
reduced (attenuated), ultimately to the point where no signal gets through.
-
Measuring cable lengths to check that they
are within specification is important and remember that attenuation increases
with network speed, so your new faster network may have cable lengths that were
fine on your old network, but are now too long.
Wiremapping
-
Most of these faults can be detected using a
continuity test, but some, like split pairs, require a signal to be sent down
the wire. Something that can send a signal or tone is required.
-
You can also use tone generators for signal
tracing and cable identification.
Connectivity Testing
- Ping tests
confirm connectivity across the network, to PCs and Network Cards.
Voltage on the wire
-
Phantom voltages or electrical noise can
cause faults on the network.
-
It’s useful to be able to check where voltages
are occurring, either intentionally or not.
Conclusion
-
As a Network Manager you will be expected to
deal with day to day cabling problems.
-
You probably can’t justify the cost of the
specialist testers used by cabling professionals, but a simple testing kit will
allow you to check for the most common problems, save you time chasing
phantoms, and help you resolve issues faster and more efficiently.
7.6.1 Solution in Faulting Cabling
1. Identify the cable. When
documentation isn't present, first locate each end of the cable. Send a digital
tone over the cable run. If there's a network patch panel, use a tone probe to
check each port on the panel for a tone. A digital probe will provide a visual
and audible signal strength indication. Once the port with full signal strength
is identified, the digital probe can be plugged into the port for 100 percent
confirmation.
2. Qualify the cable. Check the bandwidth of
any suspicious cables. A qualification tester, which checks for opens, shorts, wire
map, crosstalk, impedance faults, and cable length, generates a list of
supportable speeds. If any of the results display faults, proceed to step 3.
3. Troubleshoot disqualified results. A
qualification tester will also display any speeds that aren't supported. At the
first layer of detail, the tester will identify whether the failure is due to
faulty wire map, excessive length, and/or poor signal performance. At the
second layer, it will display the type and location of the fault.
4. Save the results. After identifying,
qualifying, and troubleshooting a suspicious cable, save the test results and
cable location in the test tool for future reference. Saving the results to a
PC that other technicians can access will prevent unnecessary duplication in
future troubleshooting efforts.
7.7
Troubleshoots in WLAN
7.7.1
Introduction
-When a wireless network fails, there are a few key areas to look to first.
- Configuration issues that
can plague a wireless LAN. With this information, we can troubleshoot our
wireless network with confidence.
- There several factors
reduce the connectivity of WLAN signal. Its also have a way to diagnose and troubleshoot WLAN.
7.7.2
Diagnose and troubleshoot WLAN
a. Check connectivity to the access
point
- First,
we should perform a communications test to see if the access point is
responding.
- Open a Command
Prompt window on a PC on our wired
network and ping our wireless access point’s IP address (ping your
router).
- The
wireless access point should respond
to the ping.
- If
it doesn’t, there’s either a break in the communications link or the access point is completely malfunctioning.
- If
the wireless client is unable to ping
the access point, the access point
could be malfunctioning.
Pinging
your access point
- Try unplugging the access point to reset it
and then plug it in again.
- Wait
for a minutes and then try pinging the
access point from both the wireless and the wired clients again.
b. Low Signal Strength
-Practically any appliance that operates on the same frequency level (2.4 GHz) as 802.11b or 802.11g can cause interference with your wireless network.
-Be sure to keep cordless phones, microwaves and
other electrical equipment at least 1m away from the access
point.
-Try changing channels on the
access point and test it out on one of the clients.
-To change the radio channel
on the access point login to the
configuration (usually a web based interface) and go to the Wireless Settings (will vary
depending on vendor/product) section, select a different channel and save
settings.
- On the client, go to Device Manager, right click your
wireless network adapter and go to Properties.
- In the advanced tab select
the Channel Property and change the
Value to the same number as the one you chose on the Access Point.
- Disable and then re-enable the
wireless connection.
Changing
wireless channels
Check
status wireless on desktop panel
c. Verify the SSID
- An SSID
is the name of a wireless local area
network (WLAN).
All wireless devices on a
WLAN must employ the same SSID in order to communicate with each other.
- Remember, if the SSID doesn’t specify the correct network,
we won’t be able to ping the access
point.
- Instead, our laptop/pc
will ignore the access point’s existence and search for an access point with
the specified SSID.
Verifing
the SSID in wireless pc card
Verifying
the SSID on Dlink Router
Verifying
the SSID on LINKSYS router
d. Verify the WEP key
- A WEP key is a security code used on
WLAN networks
- Check
out the wired equivalent privacy (WEP)
encryption configuration.
- If WEP is configured
incorrectly, we will not be able to ping the access point from a wireless
client.
- Different brands of NICs
and access points ( e.g. router)
require us to specify the WEP encryption
key differently.
- For example, one brand
requires us to enter the encryption key
in hex format, while another brand requires the key to be entered in decimal format.
Some
examples of WEP keys
- Likewise, some brands
support 40-bit and 64-bit encryption,
while other brands support only 128-bit
encryption.
- For WEP to function, all settings must match exactly between the client and the access point.
- For WEP to function, all settings must match exactly between the client and the access point.
- Wireless Encryption will
vary depending on which type of network
you are connecting to.
- In Windows XP, on the
Association tab of your wireless network properties dialog box, verify that
your network key has been entered correctly and is valid for the network you
are attempting to connect to.
- WEP is designed to help protect your computer from attack by
malicious users or by malicious software such as viruses that use unsolicited
incoming network traffic to
attack your computer.
Set WEP
Key in WLAN in CISCO router
Generate
WEP Key for your WLAN in CISCO router
e. Access Point Location
- We may also want to try changing the position of our access point antenna to improve performance.
- Change
around with its position and see if our
notice a difference.
- Sometime we find that if we point the
antenna sideways or downwards, we have better reception on the floor below. The
following images demonstrate:
Antenna pointing upwards (default)
Antenna pointing sideways
-
The location of your access point is vital.
-
Try
and place it in a central location,
as much as possible avoiding physical
obstructions and reflective surfaces.
-
Remember that
wireless signals bounce of windows and mirrors, thus decreasing the range.
f. Check the wires and wireless network adapter
-
Checking that all your wires are plugged in at the router and from the plug is one of the first things you should do –
provided of course that you have access to them.
-
Verify
that the power cord is connected and that all the lights of the router and cable/DSL modem are on.
-
This may seem like a ridiculous suggestion but you should never disregard the obvious.
-
We will also want to check that your wireless network adapter is switched on.
-
Some laptops
come with a small blue or red button on the side while others require us to
enable it from the operating system.
-
In
Windows, go to device manager and check that your wireless network adapter is enabled.
g. Check a MAC (Media Access Control) Address Filters
- MAC Address Filters are a list of MAC addresses belonging to the clients that are allowed access to the network.
- This will only permit clients with the specified MAC Addresses to communicate
with the network.
- Verify that the problematic client’s MAC is
in the address list. If the network card had to be changed or a new device
purchased recently, is sure to add it to the list.
Manufacturers
MAC for LinkSYS adapter
Other
manufacturers MAC of network interface adaptor
Set
MAC address in LinkSYS router
h. Installing a Repeater for a Performance Boost
-
If we are looking for a boost, we can always choose to install a repeater.
-
The
job of a repeater is to receive the
signal, regenerate it and rebroadcast it therefore extending the range of
your wireless network.
-
This would sit somewhere between your Access Point and your wireless client.
-
Some repeaters, like the Range Expander series from LinkSys,
don’t require it to be directly
connected to the network via a cable.
-
However, if security is an issue for you then
is careful as some of these ignore
certain security methods such as MAC address filtering.
-
Also, some
repeaters will only repeat wireless signals coming from its own product family,
-
For example if we have a D-Link Wireless
Router, we will have to get a D-Link repeater.
-
The image below demonstrates the job of a
repeater.
- The
Access Point transmits the signal. As it travels it decreases, until it hits
the repeater and gets boosted.
- The
newly transmitted signal is then received by an in-range wireless client.
Wireless repeater boost
signal
7.3 IP
Detection Problems
7.3.1
Introduction
-
TCP/IP has gone from being the protocol that
only geeks use, to a universal protocol that everyone uses, thanks to the
widespread use of the Internet.
-
TCP/IP has been around for decades and is a
solid, reliable, mature protocol. Most of the time when there is a TCP/IP related problem, the problem
is related to the way that one or more
of the hosts on the network are configured.
7.3.2 Diagnose connectivity based on IP detection
The problem raised from IP
number in several factors, but we able to diagnose it trough certain way
below:
a. Check the Configuration
- The
first step in the troubleshooting process is to check the TCP/IP configuration.
- The easiest way to do this is to open a Command Prompt window and enter the IPCONFIG /ALL command. Windows will
then display the configuration results.
- It’s
important to point out that some computers have multiple network interface
cards, and Windows may also treat a Firewire port as a network adapter.
- You
must therefore be careful to make sure that you are looking at the
configuration that’s bound to the interface that’s actually connected to the
network.
b.
Check DHCP
-IP addresses can be assigned manually (static), or via a DHCP (dynamic) server.
-If your
organization uses a DHCP server to assign IP addresses, then try entering the
following series of commands to see if the machine is able to obtain an IP
address:
IPCONFIG /RELEASE
IPCONFIG /RENEW
IPCONFIG /ALL
IPCONFIG /RENEW
IPCONFIG /ALL
c.
Check Cabling
-
If the machine is still unable to obtain an
IP address, then there are several things that could be causing the problem.
-
For example, the DHCP server might have
already given out all of its addresses. You can check the server’s logs to see
if this is the case.
-
Another possible cause is that you might have
a bad network cable.
-
Try
attaching another machine to the network cable / network jack
that the malfunctioning machine is attached to and see if the known good
machine is able to attach to the network.
d.
Check Operating system / network card related
-
Still another possible problem is that the network card is not installed
correctly through Windows.
-
In most cases, Windows XP will automatically
detect a network card and load the drivers for it automatically.
-
However, Windows XP is notorious for misidentifying network cards.
-
If you are having trouble attaching to the
network, it might be a good idea to pop
the computer’s case open and check to make sure that the make and model of
the network card that’s installed matches the driver that is loaded into
Windows.
e.
Check Driver
- If the driver matches and you are still
having problems, try going to the network card manufacturer’s Web site and downloading the newest driver for the card.
- We have seen several situations in which a new driver fixed the problem.
- If
we have tried everything that I have suggested and are still unable to acquire
an IP address, try reseating or replacing the network card.
-
Network cards have been known to go bad for no apparent reason.
Network cards updating
driver on Win XP
7.4
Troubleshoot and Helpdesk
7.4.1
Documenting Troubleshoot
a. Documenting the Solution
- Although it is often neglected in the troubleshooting process, documentation
is as important as any of the other troubleshooting procedures.
- Documenting a solution involves keeping a record of all the steps
taken during the fix not necessarily just the solution.
- For the documentation to be of use to other network
administrators in the future, it must include several key pieces of information.
- When documenting
a procedure, we should include the following information:
·
Date When was the solution implemented? It
is important to know the date because if problems occur after your changes,
knowing the date of your fix makes it easier to determine whether your changes
caused the problems.
·
Why Although it is obvious when a problem is
being fixed why it is being done, a few weeks later, it might become less clear
why that solution was needed. Documenting why the fix was made is important
because if the same problem appears on another system, you can use this
information to reduce time finding the solution.
·
What The successful fix should be
detailed, along with information about any changes to
the configuration of the system or network that were made to achieve the fix.
Additional information should include version numbers for software
patches or firmware, as appropriate.
·
Results Many administrators choose to
include information on both successes and failures.
The documentation of failures might prevent you from going down the same road
twice, and the documentation of successful solutions can reduce the time it
takes to get a system or network up and running.
·
Who It might be that information is left
out of the documentation or someone simply wants to ask a few questions about a
solution. In both cases, if the name of the person
who made a fix is in the documentation, he or she can easily be tracked down.
Of course, this is more of a concern in environments in
which there are a number of IT staff or if system
repairs are performed by contractors instead of actual
company employees.
Documenting procedure reduce
work load
Sample
of chart due to documenting procedure to solve problem
7.4.2
Help Desk
a.
Definition
- A help desk is an information and assistance resource that
troubleshoots problems with computers, software, hardware, services or similar
products.
- Corporations
often provide help desk support to their
customers via a toll-free number, website and/or e-mail.
Help desk helping user to solve problem
b.
Purpose of Helpdesk
- It
provides the users a single point of
contact, to receive help on various computer issues.
- The
help desk typically manages its requests via help desk software, such as an
issue tracking system, that allows them
to track users
requests with a unique number. This can also be called a "Local Bug Tracker" or LBT.
- Large
help desks have different levels to
handle different types of questions.
- The
first-level help desk is prepared to
answer the most commonly asked questions, or provide resolutions that often
belong in an FAQ or knowledge base.
- In a
business enterprise, a help desk is
a place that a user of information technology can call to get help with a problem.
- In many companies, a help desk is simply
one person with a phone number and a more or less organized idea of how to handle the problems that come in.
- In larger companies, a help desk may consist of a group of experts using
software to help track the status of problems and other special software to
help analyze problems (for example, the status of a company's
telecommunications network).
- Typically,
the term is used for centralized help to users within an enterprise. A related
term is call center, a place that customers call to place orders, track
shipments, get help with products, and so forth.
- The
World Wide Web offers the possibility of a new, relatively inexpensive, and
effectively standard user interface to help desks (as well as to call centers)
and appears to be encouraging more automation in help desk service.
- Some common names for a help desk
include: Computer Support Center,
IT Response Center,
Customer Support
Center, IT Solutions
Center, Resource
Center, Information
Center, and Technical Support
Center.
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