The machine can only send packets but cannot receive the packet fault handling

Our network administrator often encounters such a strange problem in daily maintenance: The machine can only send packets but cannot receive packets. The author in the long-term maintenance also ruled out a number of similar failures, so speak out to share and share, the deficiencies please criticize, correct, add.

The trouble with the NIC

Symptom: The company LAN a computer can not connect the network, the local network connection state sends the data only, but receives the packet to be 0.

Fault handling: The use of notebook computer testing, the network is normal, and then replace the PC Card, troubleshooting.

Failure Reason: Network card physical failure.

Twisted strands of trouble

Fault phenomenon: Using ADSL modem routing function, the author and six neighbors through a 10M hub to share an ADSL broadband internet, one months to normal operation. The day before yesterday, the computer suddenly can not access the Internet, ADSL virtual dial-up impassability, and the other five can be normal Internet.

Fault handling: First suspected system failure, so in Windows XP reload NIC driver, rebuild ADSL dial connection, still can not dial, and then in their own exchange with other normal access to the laptop computer, the fault is still, which excludes the computer itself problem. On the hub of the switch port, or even directly connected to the ADSL modem, the fault is still, and others use the port is normal access to the Internet, which also excludes the hub port failure. To view the local area connection, the network connection icon is normally displayed in the taskbar, there is no "X" (in fact, when the network connection icon often has an "X"), and then look at the network connection status, found that only sent packets, received packets of 0, which concluded that network connectivity problems, so check the line, See whether there is distortion or fracture, did not find abnormal phenomenon, and then in the twisted pair of ends in turn to make Crystal Head joint, the failure is not resolved. So calmly think about it, twisted pair line has four pairs of lines, Crystal Head 1, 2, 3, 4, 5, 6, 7, 8 place in turn is white orange, orange, white green, blue, Bai, green, brown, white Brown, the actual use of which is two pairs of lines, they are in the Crystal Head 1, 2 and 3, 6 position. Since the packet received is 0, it is suspected that one of the two lines is problematic (white, orange or white green, green, in fact, should be ranked in 3, the 6 position of a pair of lines for the receiving data line, so the twisted pair at both ends of the joint, in accordance with the unconventional line order: Crystal Head 1, 2, 3, 4, 5, 6, 7, 8 place in turn is white orange, Orange, Bai Lan, brown, White brown, blue, white green, green, of course still want to keep 1, 2 for a pair of lines, 3, 6 for a pair of lines. Reconnect the twisted pair, the problem is solved. In order to prove his reasoning further, White green, green this pair of lines have a problem, and later borrowed the network cable tester, and sure enough to measure white green, green this pair of lines, but because 7, 8 position on the line is a standby line, in fact, does not work, the network connection has no effect.

Failure reason: 5 UTP twisted pair has 4 pairs of lines, the actual use of which two pairs to receive and send data, due to 1, 2 or 3, 6 location of a pair of lines failure, causing network communication failures, in fact, even 4, 5 or 7, 8 position two of the line fracture will not affect network traffic.

The trouble with the VLAN

Failure phenomenon: The company's local area network through the Cisco 4006 Switch Gigabit Fiber interface with the superior headquarters, the switch has four modules, divided into three VLANs, the network has been running normally. Later, as a result of higher departments, the VLAN and IP address of the redesign and adjustment, the results of most of the company's computer can be normal network, but some computers are not normal network. In the computer can not be normal network found: Network connection icon displayed in the taskbar, the above does not appear "X", and then view the network connection status, found that only send packets, received packets of 0.

Failure handling: First suspected is the switch physical failure, but observe the switch led status and the status of each port, shown as green, the state is normal. Then use the laptop computer at the point of failure to test, the failure is still. This excludes the computer itself from failing. Then the network cable tester at both ends of the test, cable normal. Finally carefully checked the switch configuration, found that there is a set VLAN command, set VLAN 80 3/1-48,5/1-34, but in fact only 4 modules, where the module number 4 incorrectly written 5, reconfigure VLAN 80,set VLAN 80 3/1-48,4/ 1-34, troubleshooting.

Failure reason: Because the computer IP address of the port connected on Module 4 is configured according to VLAN 80, in fact, because of the configuration error, the port of Module 4 does not enter VLAN 80, these computers do not belong to any VLAN, which causes the computer to fail to communicate.

From the above three cases of fault treatment I get the following enlightenment:

Network failure should be good at analysis, and then ruled out. When the network connection icon appears in the taskbar, only send packets and receive packets of 0 o'clock, the possible cause of failure is at least: network card physical failure, network cable failure, computer IP address and switch on the corresponding port on the VLAN does not match.