Linux System Network Connection FAQ Diagnostics

Even if the network is set up step by step according to the operating instructions of the Linux system, there may still be cases where network connectivity is not possible. This is mainly because network configuration is a rather complicated matter. Sometimes experience can be more useful than technology when there is a problem with the network. There are many reasons why the Linux operating system cannot access the Internet. Here I will list some common network failures and solutions to help Linux system administrators quickly locate network errors and restore network operations in a timely manner.

The first trick: use the Ipconfig command to determine the basic configuration of the network card.

When the operating system fails to access the Internet, the Linux system administrator's first choice is to check whether the current configuration of the network card is accurate. Use the Ipconfig command to help the system administrator confirm the face-to-face configuration of the NIC. The following picture is a partial screenshot of the results displayed by the IPconfig command. So how do you judge whether this display result is normal? I will give you some ideas for your reference.

Illustration 1: IPconfig command diagram.

1. If the enterprise adopts the dynamic allocation of IP addresses, then the administrator must first determine whether the Liunxu host has obtained an IP address from the DHCP server. This mainly depends on whether the current IP address of the network card is the same as the IP network segment planned by the DHCP server. If the Linux host is not able to connect to the DHCP server or is unable to obtain an IP address from it (if the DHCP server address has been used up), the IP address shown here is often 0.0.0.0. If this happens, the system administrator You need to check the connection between this NIC and the DHCP server. Or check the usage of the DHCP server IP address pool.

2. Determine whether the current network parameter settings are accurate. Usually, if you are using an automatic IP address, then this address will not be wrong as long as it is obtained. If there is something wrong, then the host in the entire LAN will not be able to access the Internet. However, if you manually configure the IP address, it is very likely that the configuration error. For this reason, if the IP address is automatically assigned, it is only necessary to check whether the network parameters are obtained from the DHCP server. However, if it is manually assigned, it is also necessary to judge whether these parameters are accurate. Mainly check the four parameters of IP address, subnet mask, default gateway, and DNS configuration. This is the easiest place to go wrong. In particular, the IP address, it should pay attention to whether it conflicts with the current other host IP address; also need to pay attention to whether it is within the specified network segment, and so on.

3, In addition, sometimes the administrator's luck will be more prepared, may encounter the situation that the network card is not properly started (such as the network card driver is not installed correctly or the network card is temporarily disabled). At this point, network administrators often need to manually restart the network card. If you need to manually restart the NIC, you need to use the /etc/rc.d/init.d/network restart command to start. This command tells the Linux system to restart all network interfaces. After the command is run, execute the Ifconfig command again to see if the NIC is booting normally. If you still can't start, then Linux system administrators need to consider whether it is a network card or the main version of the hardware failure. You can re-plug the network card or try another network card.

In addition, there are two points to explain for these two commands. First, the role of the ifconfig command is similar to the command below Windows, but the usage is slightly different. On Windows systems, the ifconifg command has an ALL option that indicates detailed IP configuration information. When using this command, if you do not take the parameters, only the IP address, subnet mask and other information will be displayed, but if you bring this parameter, the DNS and other information will also be displayed. This requires special attention during use. In Linux, this command does not have this parameter and directly displays detailed IP configuration information. Second, the command to restart the network card needs to have certain permissions, such as root privileges. Otherwise, it will be rejected by the system.