Chapt 15 Network Troubleshooting
Spectrum Analyzer
An instrument that displays the variation of signal strength against the frequency.
Helpful in identifying problems that are specific to Windows computers that use NetBIOS naming.
NBTSTAT
Socket States
NETSTAT will display one of several states for each socket.
Tone generators and tone locators can only help you differentiate between WHAT?
UTP cables.
NETSTAT Options
-a -e -n -o -p [protocol] -r -s [interval]
NBTSTAT Options
-a [remoteName] -A [IPAddress] -c -n -r -R -S
The 4 monitoring levels supported by SNIPS are:
1. Info 2. warning 3. error 4. critical
Using nslookup you can verify that:
1. The system is configured w/ the correct DNS server. 2. The server is responding to requests. 3. The entries on the server are correct. 4. The DNS server can communicate w/ other servers in the DNS hierarchy to resolve names.
Using this kind of block system, multi-pair station cables are terminated allowing cross connection to other punch down locations.
110 Block
tone generator
A device that sends an electrical signal through one pair of UTP wires.
Smart Jack
A device that serves as the demarcation point between the end user's inside wiring and local access carriers' facilities.
Hardware Loopback plug
A special connector used for diagnosing transmission problems such as redirecting electrical signals back to itself. It plugs into a port and crosses over transmit/receive lines. The plug directly connects Pin 1 to 3 and Pin 2 to 6.
crossover cable
A special network cable used in Ethernet UTP installations, which enable you to connect devices without using a hub or a switch. The transmit and receive lines are crossed to make them work like a loopback. Pins 1 and 2 connect to Pins 3 and 6.
Troubleshooting model
A standardized step by steep approach to the troubleshooting process. A framework for correcting a problem on a network w/o introducing further problem or making unnecessary modifications to the network. The goal is to move in a methodical and repeatable manner through the troubleshooting process.
ARP cache
A table used for maintaining the correlation between each MAC address and its corresponding IP address.
Typically http://192.168.1.1 will be the address for?
Accessing the admin interface on a wireless modem.
arp -s inet_addr OR arp -s eth_addr
Add a host. The internet address is set by adding an inet_addr value and the physical address is set by adding an eth_addr value
NETSTAT -n
Addresses and port numbers in numerical form
NETSTAT -a
All connections and listening ports
Resolving Bad Connector issues
Check and replace the faulty connectors. Verify that the cables are properly secured to the connectors and are properly crimped.
Resolving Bad wiring issues
Check and replace the wires that are in bad condition.
Resolving DB loss issues
Check the cables for defects or damage, crimpling and connection with the connectors. ID and remove sources of interference.
Resolving TXRX reversed issues
Check the network port indicators on the system, if the link light is off there is an issue w/ the network adapter. replace the network adapter.
SYN_SEND socket state
Connection is active and open
NETSTAT -p [protocol]
Connections for the protocol specified in place of [protocol] in the command syntax. The value of the [protocol] variable may be TCP, UDP, TCPv6 or UDPv6.
SNY packet
Contains information regarding the return path for the data.
It can be used to test resistances between cable endpoints or voltages inside a lower power system. It should not be used to service high power or high voltage power systems
DVM - Digital Volt Meter
arp -d
Deletes a single host entry if followed by if_addr. Deletes all host entries if followed by *
Certification Tester
Determine whether a cable meets specific ISO or TIA standards (Cat5,6 or 7). Should be used if a network is wired with both copper and fiber.
arp -N if_addr
Displays the ARP entries for the network interface specified by if_addr
nbtstat -c
Displays the NetBIOS name cache of the local computer
nbtstat -A [IP address]
Displays the NetBIOS name table of the remote computer specified by the IP address
nbtstat -a [remote name]
Displays the NetBIOS name table of the remote computer specified by the name.
arp -a and arp -g
Displays the current ARP entries in the cache. Can add inet_addr to specify a particular IP address.
Step 7 of The Network + Troubleshooting Model
Document findings, actions and outcomes.
DIG utility
Domain Internet Groper: Unix/Linux command line tool that can be used to display name server information. Easier to use than nslookup. It is included with the BIN version of DNS and can be downloaded from many UNIX and Linux resource sites on the Internet.
Interactive mode w/in nslookup utility
Enables you to query name servers for information about hosts and domains.
Step 4 of The Network + Troubleshooting Model
Establish a plan of action to resolve the problem and ID potential effects: Establish a plan of action b/f you start making changes, once you have determined the probable cause. Detail each step that you will take while attempting to resolve the issue.
Step 2 of The Network + Troubleshooting Model
Establish a theory of probable cause: Question the obvios
NETSTAT -e
Ethernet statistics
Loopback Wiring standards
Ethernet: Pin1 to 3 and Pin 2 to 6 T1: Pin 1 to 4 and Pin 2 to 5
FCS errors
Frame Check Sequence: The extra characters added to a frame for detecting and correcting errors.
Environment Monitors
Hardware tools that ensure that environmental conditions do not spike or plummet temperature above or below equipment specifications.
Step 1 of The Network + Troubleshooting Model
ID the problem: question users, re-create the problem, ID the symptoms, and determine if anything has changed.
Resolving Split cables issues
Identify the split cables and replace them with compatible cables.
Step 5 of The Network + Troubleshooting Model
Implement the solution or escalate as necessary: Implement the plan of action step by step to fix the problem. Or, escalate the issue to the appropriate personnel.
Wireless Connection Issues
Interference Incorrect encryption levels Channel congestion Incorrect frequency SSID mismatches Standard mismatches Distance Bounce Incorrect antenna placement Configuration Incompatibilities Incorrect channel Latency Incorrect switch placement
Arp utility
It supports the arp service of the TCP/IP protocol. It enables the administrator to view the arp cache and add or delete cache entries.
nbtstat -S
Lists NetBIOS connections and their state with destination IP addresses.
nbtstat -s
Lists NetBIOS connections and their state, converting destination IP addresses to computer NetBIOS names.
nbtstat -r
Lists the NetBIOS names resolved by broadcast and via WINS.
nbtstat -n
Lists the local NetBIOS name table along with the service code, type and status.
Qualification tester
Measure the speeds at which a network can transmit data. Used to troubleshoot a network but not to test networks. It tests the continuity of UTP/STP cables and verifies the adherence to 10BASE-T, 100BASE-T, TIA568A, TIA-568B and Token ring wiring standards. Verifies ring wiring standards and shield integrity.
A windows utility that is used to view and manage NetBIOS over TCP/IP(NetBT) status information.
NBTSTAT
NBTSTAT utility
Name resolution: It can display NetBIOS name tables for both the local computer and remote computers and also the NetBIOS name cache. The table names enables you to verify the connection establishment. You can refresh the NetBIOS name cache as well as the names registered with the WINS server. Developed specifically as a NetBIOS diagnostic tool.
Cable stripper
Often part of a wire crimper, allowing the user to strip wires of their protective coating and then use the crimping tool to attach a media connector.
CLOSE_WAIT socket state
Passive close. The server just received FIN_WAIT_1 from a client.
MUT - black hole
Places in the network where incoming or outgoing traffic is silently discarded or dropped w/o informing the source that the data did not reach its intended recipient.
Logical Connectivity Issues
Port Speed Port duplex mismatches Incorrect VLAN assignment Incorrect IP address Wrong gateway assignment Wrong DNS server assignment Wrong subnet mask Power Failure Bad/Missing Routes
Non-interactive mode w/in nslookup utility
Prints only the name and requested details for one host or domain. Useful for a single query.
Digital Volt Meter (DVM)
Provides scales for reading voltage in both AC and DC and different resistances.
Insulation Displacement Connector is the technical name for a?
Punch Down tool.
nbtstat -R
Purges the cache and reloads static entries from the LMHOSTS file
Straight-through
RJ45 cable that is commonly used for network connectivity. Pins 1 and 2 transmit and Pins 3 and 6 receive.
NETSTAT [interval]
Refreshes and redisplays the statistics specified in the command at the stated number of seconds specified in place of [interval] in the code syntax.
TCP/IP based programs
SMTP and FTP
nbtstat -RR
Sends name release packets to the WINS server and then starts refresh.
NETSTAT utility
Shows the status of each active network connection. Will display statistics for both TCP and UDP, including protocol, local address, foreign address and the TCP connection stat. Not the UDP stat b/c UDP is connectionless.
Socket
Software in an OS that connects an application with a network protocol.
NETSTAT -s
Statistics grouped by protocol -IP, IPv6, ICMP, ICMPv6, TCP, TCPv6, UDP and UDPv6
Routing and Switching Connection Issues
Switching Loop Routing loop Routing problem Proxy arp Broadcast storms Port configuration VLAN assignment Mismatched MTU/MUT blackhole
Open impedance mismatches
Symptoms: An echo on either the talker or listener end of the connection. Causes: Mismatching of electrical resistance. Resolution: Use TDR to detect. Collect and review data, interpret the symptoms, determine the root cause.
Bad cables/improper cable types
Symptoms: Cables that connect different parts of a network are cut or shorted. Causes: When the wire conductor comes in contact with another conductive surface, changing the path of the signal Resolution: Use cable testers. After you ID the source of the issue, move the cable to prevent it from coming in contact with other conductive surface.
Interference - (Electro Magnetic Interference -EMI)
Symptoms: Crackling, humming and static. Low throughput, network degradation, and poor voice quality. Causes: Radio Frequency (RF) interference - cordless phones, Bluetooth, cameras, paging systems, unauthorized APs and client in the ad-hoc mode. Resolution: Remove or avoid environmental interferences. Ensure adequate LAN coverage. Test area prior to deployment using tools such as spectrum analyzers.
Bad/Missing Routes
Symptoms: The router is sending packets using an invalid path. Causes: The router setting is incorrect. Resolution: Check and change the router setting and reboot the router for the changes to be effected.
Power Failure
Symptoms: There is a power failure that affects switches and routers. Causes: Switch and router adapters connect to cable modems which depend on the availability of power. Resolution: Use cable modems and other network devices w/ battery backed power supplies to ensure that there is uninterrupted service of several hours in case of local power failures.
TRUE/FALSE: SSIDs are case sensitive.
TRUE
Step 3 of The Network + Troubleshooting Model
Test the theory to determine cause: Determine next step to resolve the problem
Network cable certifier
Test transmission speed and performance
LAN tester
Test transmission speed, cable skew, cable propagation delay, cable typing (CAT3, 5,5e,6), attenuation, and cable verification. Carries out a cable conduction test and a miswiring detection test.
What is an initial step in diagnosing general connectivity problems?
The Ping Utility. It is the most commonly used ICMP command.
TIMED_WAIT socket state
The client enters this state after FIN_WAIT_1
FIN_WAIT_2 socket state
The client just received an acknowledgement of its FIN_WAIT_1 from the server.
ESTABLISHED socket state
The client received the server's SYN and the session is established.
FIN_WAIT_1 socket state
The connection is active but closed.
NETSTAT -o
The process ID associated w/ each connection
Troubleshooting
The recognition, diagnosis and resolution of problems.
NETSTAT -r
The routing table
LAST_ACK socket state
The server is in this state when it sends its own FIN.
LISTEN socket state
The server is ready to accept a connection
SYN_RECEIVED socket state
The server just received the synchronize flag set (SYN) from the client
CLOSED socket state
The server received an acknowledgement (ACK) from the client and the connection is closed.
Maximum Transition Unit (MTU)
The size in bytes of the largest protocol data unit that the layer can pass onwards.
If there is a bad connection, this usually means...
There are no bytes in the send or receive queues.
What is a common first step when dealing with TCP/IP networking problems?
To verify that the host's IP addressing information is correct, using IPconfig or IFconfig.
Voltage Event Recorders
Tool used in conjunction with or in addition to a voltmeter to test and verify that the electrical signals transmitting through the network cables are within the required specifications.
Resolving Open, short cables issues
Use cable testers and locate open or short cables. repair the cables and recheck that the issues are resolved if not replace the cables.
Wireless LAN Survey Software
Used for wireless planning. Simulates WLAN performance. Can determine network coverage areas
66 Block Type of punch down block
Used in the telephone industry to terminate telecommunication. supports low-bandwidth telecommunications transmission.
arp eth_addr
Used w/ other options to specify a physical address
arp inet-addr
Used w/ other options to specify an Internet address.
arp if_addr
Used w/ other options to specify the Internet address of the interface whose ARP table should be modified.
Step 6 of The Network + Troubleshooting Model
Verify full system functionality and if applicable implement preventative measures.
Resolving Cable placement issues
Verify that the cable is placed away from source of EMI. ID and removed the sources of interference.
Resolving Distance issues
Verify that the cables are run only for the maximum distance they are supported. ie.. if an Ethernet cable exceeds 100 meters, the signal will deteriorate.
Simple Cable Tester
Will determine whether a cable has an end to end connection and can detect shorts or opens but cannot certify the cable for transmission quality.
Give an example of two Network Analyzers
Wireshark Microsoft Network Monitor.
If the error count is high, it could be....
a problem with the card, or could indicate generally high network traffic.
110 Block Type of punch down block
aka Cable Termination block used for structured wiring systems. Supports higher bandwidth than 66 block and is suitable for use in data applications.
Cable Tester
aka Media Tester: An electrical instrument that verifies if a signal is transmitted by a cable.
Network Analyzers
aka packet or protocol analyzer or packet sniffer: a software or hardware tool that integrates diagnostic and reporting capabilities to provide a comprehensive view of an organizations network.
Tone Locator
aka tone probe: a device that emits an audible tone when it detects a signal in a pair of wires.
Multimeters
aka volt/ohm meter: An electronic measuring instrument that takes electrical measurements such as voltage, current and resistance. Can be analog (AMM) or digital (DVOM)
Arp Options
inet_addr eth_addr if_addr -a -g -N if_addr -d -s inet_addr eth_addr
What can you use to display information about DNS servers?
nslookup
what can you use to determine what is performing name resolution and if it's doing it correctly?
nslookup
nslookup syntax
nslookup [-option ...] [computer-to-find | - [server] ]
demarc
A demarcation point where the bldg.'s wiring ends and the telephone company's wiring begins. aka hand off
Electrical Safety Rules
- Professionals should service high-power equipment. - Always disconnect b/f servicing - Work with a partner - Never bypass safety devices. - Use anti-static devices - Perform only the work for which you have sufficient training. - Do not attempt repair work when you are tired. - Do not assume anything w/o checking it out for yourself. -Do not wear jewelry or other articles that could accidentally contact circuitry and conduct current. - Wear rubber-soled shoes to insulate yourself from ground. - Suspend work during an electrical storm. - Do not handle electrical equipment when your hands or feet are wet or when you are standing on a wet surface. - Prevent static electricity from damaging components by standing on a totally insulated rubber mat to increase the resistance of the path to ground.
NETSTAT Utility has several functions
- Use it to find out if TCP/IP based program is listening on the expected port. - Check statistics to see if the connection is good. -Use statistics to check network adapter error counts - Use it to display routing tables and check for network routing problems.
Time Domain Reflectometers (TDR)
- Used for detecting cable problems. -Sends an electrical signal out onto the wire and analyzes the signal on its return. -Can detect: bends, short circuits, connector problems, termination problems on coax networks. -Optical TDR
Network Technician's Hand Tools
1. A variety of screwdrivers and spare screws 2. Long-nose pliers 3. Small diagonal cutting pliers. 4. A small adjustable wrentch 5. A variety of wrenches or nut drivers. 6. A small AA or AAA flashlight 7. An anti-static wrist strap with clip
Types of Cable Testers and Certifiers
1. Certification Tester 2. Qualification Tester 3. LAN tester 4. Network cable certifier
The Network + Troubleshooting Model (7 steps)
1. ID the problem 2. Establish a theory of probable cause 3. Test the theory of determine cause 4. Establish a plan of action to resolve the problem and ID potential effects. 5. Implement the solution or escalate as necessary 6. Verify full system functionality and if applicable implement preventative measures. 7. Document finding, actions and outcomes.
Ping Responses
1. Normal - the computer responds w/ requested data 2. Destination unreachable - target computer was ID'd but unreachable by the default gateway. 3. Unknown host - target computer is unknown and is not reachable. 4. Destination does not respond - there is no response to the ping. 5. Network or host unreachable - routing table does not contain an entry for the network or host.
The ping Utility steps:
1. Ping the loopback address 127.0.0.1 2. Ping a specific system: to verify that is is running and is connected to the network. 3. Ping by IP address: to determine if is is a problem related to name resolution 4. Localize the problem: ping the local loopback address; ping the systems' own IP address; ping the address of the default gateway; ping the address of a remote host.
2 main Types of punch down blocks
66 Block 110 Block
Fox and the Hound
A combination of a tone generator and a tone locator.
Wire crimper
A tool that attaches media connectors to the ends of cables. Used to trim the ends of a cable.
Wireless Testers
A wifi spectrum analyzer used to detect devices and point of interference as well as analyze and troubleshoot network issues on a WLAN or other wireless networks.
Circuit Testers
An electrical instrument that is used for testing whether or not current is passing though the circuit. Plugs into socket and displays circuit status.
Categories of Multimeters
Category I - Conditions where current levels are low. Category II - Interior residential branch circuits Category III - Distribution panels, motors and appliance outlets. Category IV - High-current applications ie..service connections, breaker panels for wiring mains, and household meters.
Physical Connectivity Issues
Crosstalk Near end cross talk Attenuation Collisions Shorts Open impedance mismatches Interference Bad modules (SFPs, GBICs) Cable problems Bad cables/improper cable Types
Proxy arp
Symptoms: The proxy server is not functional. Causes: The proxy settings are misconfigured or down. may lead to DoS attacks. Resolution: Correct the proxy settings to resolve the issue.
Types of LED Indicators
Link Indicators - indicate signal reception from the network. Activity - Flickers when data packets are received or sent. Speed - whether the adapter is operating at 10Mbps, 100Mbps or at 1Gbps. Dual color - Indicate different network states.
Voltmeters
Measures voltage and resistance b/t two points in a circuit.
Latency
Symptoms: Delay in data transmission on the network is very high. Causes: The signal strength is weak or the position of the wireless antenna is modified. Resolution: Verify that the wireless modem is functional. Change the antenna position to the position that gives the best performance. Ensure that your antenna is maintained at the same position.
Collisions
Symptoms: High latency, reduced network performance, and intermittent connectivity issues. Causes: occur on networks as nodes attempt to access shared resources. Resolution: Depends on the network. ie.. replacing a hub for a switch will fix it.
Incorrect encryption levels
Symptoms: If the encryption types or keys b/t two devices do not match, no connection is established. Causes: Improper configuration and different encryption types. Resolution: Ensure that security settings match between and among devices.
Port duplex mismatches
Symptoms: Late collisions, port alignment errors, and FCS errors are present during testing. Causes: Configuration errors. Occurs when the switch port and a device are configured to use a different set of duplex settings, or when both ends are set to auto negotiate the settings. Resolution: Verify that the switch port and device are configured to use the same duplex setting.
Distance
Symptoms: Low signal strength and throughput. Issues that can occur b/c of low signal strength include latency, packet loss, retransmission or transient traffic. Causes: The distance b/t two points causes this connectivity issue. The longer the distance b/t two devices the lower is the signal strength. Resolution: Add another access point to increase coverage. use a spectrum analyzer to determine coverage and signal strength.
Interference on a Wireless connection
Symptoms: Low throughput, network degradation, dropped packets, intermittent connectivity and poor voice quality. Causes: RF interference can be caused by a number of devices including cordless phones, bluetooth, cameras, paging systems, unauthorized APs, metal building framing, and clients in ad-hoc mode. Resolution: Remove or avoid environmental interferences as mush as possible.
Mismatched MTU/MUT black hole
Symptoms: MTU is inaccessible Causes: In case of a mismatch of the MTU, the TCP/IP connection handshake does not occur b/t the devices (routers) and the connection cannot be established. Resolution: Reconfigure the MTU to check whether the problem gets resolved. If not replace the device.
Incorrect frequency
Symptoms: No connectivity Causes: Devices must operate on the same frequency. 5GHz cannot communicate w/ 2.4GHz. Resolution: Deploy devices that operate on the same frequency.
Wrong DNS server assignment
Symptoms: No connectivity between devices Causes: A device is configured to use the wrong DNS server Resolution: Open TCP/IP properties and check the IP address of the DNS server listed for the client. Replace w/ the correct IP address and test connectivity.
Incorrect VLAN assignment
Symptoms: No connectivity between devices Causes: Devices are configured to use different VLANs Resolution: Reconfigure devices to use the same VLANs
Incorrect IP address
Symptoms: No connectivity between devices Causes: Either the source or destination device has an incorrect IP address. Resolution: Use Ping cmd to determine if there is connectivity between devices. Check IP addresses and empty the ARP cache on both computers.
Wrong subnet mask
Symptoms: No connectivity between devices Causes: Either the source or destination device has an incorrect subnet mask. Resolution: Use the ping cmd to determine if there is connectivity b/t devices. Check the subnet mask on both devices. Change the incorrect subnet mask to a correct one and test connectivity.
Wrong gateway assignment
Symptoms: No connectivity between devices Causes: The IP address of the gateway is incorrect for the specified route. Resolution: change the address of the gateway to the correct address.
Standard mismatches
Symptoms: No connectivity between devices. Causes: Devices are configured to use different standards such as 802.11a/b/g/n Resolution: Devices chosen to work together should use the same standard to operate.
SSID mismatches
Symptoms: No connectivity between devices. Causes: Devices are configured to use different ESSIDs. Resolution: Set the devices to use the same SSID. Ensure that the wireless client and the access point are the same.
Bounce
Symptoms: No or low connectivity b/t devices. Causes: Signals from device bounce off obstructions and are not received by the receiving device. Resolution: Move one of the devices to avoid obstructions. Monitor performance and check for interference.
Incorrect antenna placement
Symptoms: No or low signal and connectivity. Causes: The position of your antenna can negatively affect overall performance if placed incorrectly. Resolution: Alter the position of your antenna and monitor device performance.
Port Speed issues
Symptoms: No or low speed connectivity b/t devices. Causes: Ports are configured to operate at different speeds and are therefore incompatible w/ each other. Resolution:Verify that equipment is compatible and is operating at compatible speeds.
VLAN assignment
Symptoms: Nodes on the network cannot communicate w/ one another. Causes: By default, computers on different segments are added to different VLANs and they cannot communicate with one another unless the switch is configured to allow communication b/t computers on different VLANs. Resolution: Check the VLAN assignment on the switch console and reassign the computers to the VLAN to enable communication among them. Ensure that the IOS of the switch is updated to reflect the latest settings.
Routing problem
Symptoms: Packets do not reach their intended destination. Causes: This could be caused by configuration problems, route convergence, broken segments or router malfunctioning. Resolution: Verify that the router is functional. replace the router.
Port configuration
Symptoms: Port configuration is incorrect. Causes: The recent changes made to the port were incorrect. Resolution: On the system console of the switch, verify the port properties of the individual nodes and check their status. if needed restore the port configuration to is default setting from the last backup.
Near end cross talk
Symptoms: Signal loss or interference Causes: occurs near the terminating connector along the transmitting end of the cable. Resolution: Test with cable testers on both ends. verify the cable is terminated properly and that the twists in the pairs of wires are maintained.
Cross-talk
Symptoms: Slow network performance and excess of dropped or unintelligible packets. users hear garbled voice. Causes: two cables run in parallel and the signal of one cable interferes with the other. Crossed or crushed wire pairs in twisted pair cabling. Resolution: Use twisted pair cabling or use digital signals. Maintain proper distance b/t cables.
Attenuation
Symptoms: Slow responses from the network Causes: degradation of signal strength Resolution: For wired networks use shorter cable runs. For Wireless use more access points and signal boosters. Evaluate the environment for interference.
Incorrect switch placement
Symptoms: Switch performance is considerable reduced. Causes: There is a conflicting device in the range which is causing the interference. Resolution: Locate the conflicting device and move it to another location. if you can't then rework your network layout and determine a better position for the switch so that there is no conflict w/ the other devices. Monitor the switch performance periodically to prevent further occurrence of the issue.
Bad modules (SFPs, GBICs)
Symptoms: System console on the switch may use distinct colors ie.. amber or red to help you locate the faulty SFPs/GBICs. No communication through the faulty device. Causes: Modules in SFPs/GBICs get corrupted. Resolution: Replace the faulty SFPs/GBICs
Broadcast storms
Symptoms: The network becomes overwhelmed by constant broadcast traffic generated by a device on the network. Causes: There are too many broadcast messages being send parallelly causing high network traffic. Resolution: ID the device and reconfigure it to increase the interval of broadcast messages. On the network, apply restrictive settings to prevent network nodes from sending broadcast messages. Cisco uses Link Aggregation to prevent broadcast storm. Spanning Tree Algorithm can also be used.
Incompatibilities
Symptoms: The wireless device is not accessible from the client. Causes: The settings on the wireless device is not compatible with the clients. Resolution: Check the configuration of the wireless modem by accessing the web admin interface. Verify that the client systems can support the same configuration. ID the configuration supported on both the client and the server and apply the same on the wireless device and the client systems.
Incorrect channel
Symptoms: The wireless signal is not accessible even within the expected range. Causes: Most common cause could be another wireless device or application that operates at the same frequency level creating a conflict. Resolution: ID the conflicting device and move it to another location that is outside the reach of the Wireless access point. If you can't relocate it change the channel of one of the devices.
Routing loop
Symptoms: There is a routing loop on the network. Causes: Packets are routed in a loop. Resolution: Recheck the router configuration and adjust it to prevent a routing loop.
Switching Loop
Symptoms: There is a switching loop on the network Causes: Packets are switched in a loop Resolution: A switching loop needs STP to ensure loop free switching of data. Rework on the network arrangement and cabling to prevent the switching loop. Use Spanning Tree protocol - it will turn off those redundant links.
Channel congestion
Symptoms: Very slow speeds Causes: Interference from neighboring wireless networks; congested network channels. Resolution: Many wireless routers are set to autoconfigure the same wireless channel. log into the router and manually change the channel the wireless router is operating on.
Configurations
Symptoms: Wireless modem is active, but clients cannot access the Internet. Causes: Configuration of the wireless modem is incorrect. Resolution: Check wifi modem configuration via the web admin interface. Cehck the encryption type, SSID and pass phrase text that is specified and confirm that the wifi modem was rebooted after the configuration change. Check that the clients can support the same encryption type. Verify that the same SSID and key phrase are defined in the network connection. Verify that the wifi receiver on the desktop system is configured properly w/ correct compatible drivers installed.
Electrical Shorts
Symptoms: complete loss of signal Causes: 2 nodes of an electrical circuit that are meant to be at different voltages create a low resistance connection causing a short circuit. Resolution: Use a TDR to detect and locate shorts. Replace cables and connectors.
Cable problems
Symptoms: nodes on the network cannot communicate. the routers, switches and individual nodes on the network work but the problem still persists. Causes: problems with network cables. Resolution:Identify the issue with the network cable and determine a suitable solution.
SNIPS
System and network Integrated Polling Software: A system and network monitoring software tool that runs on UNIX systems. It offers both a command-line and web interfaces to monitor network and system devices. The monitoring functions of SNIPS determine and report the status of services running on the network.
Troubleshooting w/ IP configuration Utilities
Use ipconfig or ifconfig to determine if the host is configured for static or dynamic IP addressing and if it has a valid IP address.
Punch Down Tools
Used in a wiring closet to connect cable wires directly to a patch panel. Strips insulation and embeds wire into the connection at the back of the panel.
Punch Down Blocks
Used to connect one group of telephone and network wires with another group in utility or communication closets. Typically support low-bandwith Ethernet and Token Ring networks.
T1 Crossover
Used to connect two T1 CSU/DSU devices by using T568B pairs.
Cable Certifiers
Used to perform tests ie. cable testing and validity testing. useful in finding short circuits and other faults. helpful in determining mode of connectivity devices ie. full duplex and half duplex.
Optical Time-Domain Reflectometer
Used to test fiber optic cabling: Detects fiber length, location of faulty splices, breaks and bends; measures attenuation.
Traceroute Utility
You can use it to determine where the communication fails. Issue the cmd from the local machine to see how far the trace gets before you receive an error message. Using the IP address of the last successful connection you will know where to begin troubleshooting the problem.
Butt set
aka Lineman's test set: A special type of telephone handset used by telecom technicians when installing and testing local lines.
LED Indicators
located on network adapters, switches, routers, and cable and DSL modems can give you information about the status of the network connection.
NSlookup Utility
used to test and troubleshoot domain name servers. it has 2 nodes. Interactive mode and non-interactive mode. It's available in UNIX and all Windows systems except Win9x and Win ME.
