Network failure is inevitable, it is important to quickly isolate and troubleshoot. Network maintenance personnel should be equipped with corresponding tools and corresponding knowledge for timely, effectively, and solve problems. This article discusses ten ambiguous issues that network technicians and engineers often encounter. First analyze the problem, then discuss how tools use to help find and fail. It is designed to give a throwing jade.
A, arresting the abuse of the physical layer
User complaint - can not log in or interrupt
Symptom - only affecting a workstation, and the station is originally no problem
Find a problem:
The cable terminal link is too long. Users move, bend, connect, and cut off network terminals (especially when laptops). Cheap cable testers can check this problem. Before you can say it is the problem of cable, you usually first consider the problem of cables. This requires a network test tool to prove whether the health status of the local network segment is good, whether the hub port function is normal, whether the network card and its driver work are good. Finally, check if there is a problem with the network interconnection device. Only when you know where you have problems with a problem with a problem with a problem, the disconnected connector or a ground loop should start testing the cable. In the copper-axis network, search for breaking between coaxial "T-head" and NIC cards, in the UTP network, continuously run the instrument graph test function, and the terminal is constantly moving to identify contact or short circuit.
Solve the problem:
Replace the workstation connection cable, replace the damaged connector, or stop using the horizontal cable. Take a completely check the processed cable again.
B. Fast Ethernet is slower than the upgrade Ethernet
User complaining -10Mbps Ethernet speed slowly, upgrade to 100Mbps Fast Ethernet and even unable to connect the Internet.
Symptoms - Workstations affecting new workstations or upgrades.
Find a problem:
For the UTP5 non-shielded twisted pair, the cable tester is tested whether it meets the EIA / TIA-TSB67 standard corresponding to 100 Mbps transmission rate. Certain cable links working in 10Mbps Ethernet work are not working properly because the proximal crosstalk is too large at 100Mbps Ethernet. The signal is coupled to the neighboring line to cause high frequency signal transmission failure. The line of UTP is separated and even makes the network to be paralyzed at a certain flow.
Solve the problem:
Replace or deactivate the links that cannot be connected, the fault is cleared and then all the links placed at the time.
C, invalid watchdog
User complains - NetWare remote server that cannot connect to Novell network
Symptom - affect all workstations connected to the server within this network segment
Find a problem:
Check the health of the network segment, pay attention to observe the utilization rate, collision, error frame, and broadcast frame level. At this point, a large number of collisions or error frames can be observed, the collision or error frame can cause a delay in the "Hello" frame between the client and the server. The remote network segment of the server specified again is repeated this test. If both network segments appear blank, use the Network Tester to query the SNMP proxy in the router, check the routing table between the two network segments. Determine that there is no crowding problem. In order to effectively use resources, the Novell server cancels the client if the client does not respond to the "Hello" frame if the watch is allowed.
Solve the problem:
When you simply change the watchdog, the delay parameters are changed, and the parameters in the Novell server are changed. If the situation is improved, it can be determined as a cause of the frame loss, correct the parameters of the watchdog delay frame timer.
D, Jumei chain effect
User complaint - network service is slow
Symptom - affects all users of an Ethernet segment. Network service (access server) is slow, but it is independent of a server connected.
Find a problem:
The network tester is connected to the hub and running network health test in peak hours. A large amount of error frame will be observed. In the 10BASE-2 network, the type of error frame is classified as "delay collision". The type of frame error in the 10BASE-T network is classified as a typical frame school sequence error (FCS error), and the newly added hub is usually effectively formed with the original hub as the network user grows. Solve the problem:
Statistically, the number of repeaters passing between two network devices. There should be more than 4 in 10Mbps Ethernet, and there should be no more than 2 in the 100Nbps fast Ethernet. If the quantity exceeds the standard, the network topology is corrected according to the standard of the Ethernet, and then the error is still incorrect.
E, IP network manager's retribution
User complaining - a workstation gap error, can't log in or cannot access remote servers
Symptom - only affecting a workstation, which is usually increasing, moved, and changing the workstation after changing the workstation.
Find a problem:
First eliminate the potential problem with your users with accounts and security settings. Let the user log in and try to repeat this operation from another workstation. If successful, you can use the network tester from the link status between the user to the server. Then test the network card, detect the functions and conditions of the hardware and drivers. If there is no problem, check the IP settings, determine if the user's IP address is valid or has a duplicate IP address. Determine whether the subnet mask of this network segment and whether the default address of the router is correct, the DNS server (if any) is dedicated. If the IP address of a new workstation is repeated with the IP address of the print server, each person's printing will point to the new client.
Solve the problem:
Change to the right setting, then restart the workstation
G, fiber optic
User complaint - the whole network slows down
Symptom - affects all workstations connected to the network segment
Find a problem:
In the normal network usage, connect the network tester to the hub, generate traffic on both ends of the fiber connection, and every side of health. Disconnect or attach the optical fiber at a certain moment, and whenever the fiber is connected to the network segment, a large amount of error frame is observed. Inferior fiber link connectivity generates a large amount of garbage frame in its subsidized segment, forcing the workstation to rehabilize the frame, the network speed slows down.
Solve the problem:
Clean or reinstall the fiber optic connector, reset all connector, check the network health again, and there should be only a small amount of error frame.
H, strange! Is the cable hit at night?
User complains - can not connect to the Internet or not land
Symptoms - there is only one work station on the network segment to access the Internet
Find a problem
Disconnect the connection cable of the workstation, connect the network tester, pay attention to the connection signal from the hub. Run the cable test to see if the cable from the office to the wiring is open. If the length is normal, set the tool in the audio generator position, from the wiring audio detector to the cable, usually, when there is a change in the wiring, the cable clues will be pushed and collided. Causes the connector to fall off or loose.
Solve the problem:
Reissue the cable connector between the workstation and the workstation and hub, check if the connection signal indicator is shining, determine if the user can access the Internet.
I, "Patient" heart is still jumping?
User complaining - the speed of the network busy manuscript is very slow
Symptom - All workstations of individual network segments do not respond to the servers of this network segment or other network segments.
Find a problem:
The network tester is connected to the segment during peak hours. Network health test running the network segment, pay attention to the network's utilization, collision, error frame, and broadcast frame conditions. At this time, it may see that the average collision rate is abnormal, and the observed flow may be as high as 50% of the collision frame fragment. . This is the performance of the frame signal transmission and reception error - SQL (Signal Quality Error). The "Heartbeat" signal is inadvertently staying in "Bo".
Solve the problem:
Positioning each signal transceiver in the network. Check if the SQE switch is located in the "Off" location. This signal is used in early 10Base-5 Ethernet, and new Ethernet devices are no longer used. J, can be connected, but don't login
User complains - the server that cannot be connected to
Symptom - Problem Normally, then install or reset the workstation, but is limited to one workstation
Find a problem:
Disconnect the workstation connection, connect the network tester, execute ipxping or then obtain the server list later to check which layer of the network protocol configured. Pay attention to the frame package package (for example, 802.2). You can now test the NIC, check if the installation and running procedures are correct. Also pay attention to check the network card binding frame type (such as 802.3). The two frame types must match if the server and workstation are running different, and the Internet cannot be connected.
Solve the problem:
Use Editor to open the workstation Net.cfg, modify one line: After the Frame-ethernet-802.3 is changed to Frame-Ethernet-802.2, connect the workstation to the network, restart. Check the server connection status.
K, inexplicable intermittent connection interruption
Support complaint - the service speed is too slow, the connection intermittent interruption
Symptoms - The problem is only again on a website, which is not related to the proxy server being accessed.
Find a problem:
Disconnect the website, connect a traffic transmission (this is part of the diagnostic process) function test tool, check the network's utilization, collision, and error frame levels, and determine if the network is healthy. If the instrument detects is only the time break, it is typically a physical layer failure. Cable link test (including a user connection cable), at which point the length test may display the cable long (UTP cable is 100 meters, the copper shaft cable is 185 meters). The allowable length of the IEEE is exceeded, which will cause serious attenuation of the transmission signal in the local area network.
Solve the problem:
Add a repeater in the link to limit the cable length to the allowable range. Another way is to replace the cable or copper axis with an optical fiber.
