Common switch fault symptom classification and troubleshooting methods

When using a vswitch, it is inevitable that a fault will occur. Therefore, we should take measures to eliminate the switch fault and have a certain understanding of common faults. In large-scale LAN networks, network channels are often severely congested. There are many reasons for this switch failure, such as virus attacks on the network, hardware damage on the network device, and transmission bottleneck on the network port.

However, according to the statistical probability of network congestion, switch failures are most likely to occur when the network is changed or changed, because network loops are easily triggered when the network is frequently changed, network congestion caused by network loops is often concealed, which is not conducive to the efficient troubleshooting of switch faults. Can we find a suitable solution to effectively solve the network channel congestion caused by the network loop? In fact, with the clever configuration of the switch's loop monitoring function, we can quickly determine whether there is a network loop in the LAN, so that the switch failure caused by the network loop can be quickly solved!

How to judge the network loop

Because almost all newly purchased switches support the port loop monitoring function, we can use this function to automatically determine whether a network loop occurs on the specified communication port. Once the loop monitoring function is enabled on the specified Ethernet communication port, the switch device can automatically and periodically scan and monitor all communication ports to determine whether the communication port has a network loop. If a switch port is monitored as a network loop, the switch port is automatically in the loop monitoring status, according to the switch port parameter settings and port type, the switch will automatically shut down the specified switch port or automatically report the log information of the corresponding port. In the future, we only need to view the log information or according to the port enabling status, you can quickly determine whether a network loop exists in the LAN. Now, this article takes the H3C S3050 vswitch as the operating blueprint and describes the specific configuration steps for judging the network loop phenomenon by using the loop monitoring function.

Enable port loop monitoring

To enable the switch to automatically determine whether a network loop exists in the local LAN, We need to enable the port loop monitoring function of the switch and enable the port loop monitoring control function. However, by default, these functions are all disabled. You need to manually configure the switch to enable the monitoring function of the specified port and the controlled function of the port.

When you enable the port loop monitoring function of a vswitch, you can log on to the vswitch background management page as a system administrator and enter the string "sys" at the command line prompt ", click the Enter key to switch the switch to the system view. Then, in the System View, run the "loopback-detection enable" string command ", in this way, the global port loop monitoring function of the vswitch is enabled successfully. Next, we also need to enable the loop monitoring function of the specified Ethernet switch port of the switch. For example, if we want to enable the loop monitoring function of the Ethernet 16 port, in the system view of the switch, enter the string command "interface GigabitEthernet 1/0/16" and click the Enter key. Then, the interactive machine configuration status enters the view of port 16 of the Ethernet, at the same time, the command line prompt of the switch will automatically change to "H3C-GigabitEthernet1/0/16". At this command line prompt, run the string command "loopback-detection enable" again ", in this way, the switch's Ethernet 16 port loopback monitoring function is successfully enabled;

Next, we also need to enable the network loop monitoring control function for both the Hybrid port and the Trunk port in the Ethernet port 16 view. When this function is enabled, we just need to execute the string command loopback-detection control enable at the H3C-GigabitEthernet1/0/16 command line prompt.

Loop monitoring for different VLANs

With the above configuration, the switch system can only perform network loop monitoring in the default VLAN of the Hybrid and Trunk ports under the specified Ethernet port, but cannot perform automatic monitoring on other VLANs, in this way, if there is a network loop in other virtual working subnets in the LAN, the switch still cannot be automatically determined. Therefore, we need to make appropriate settings so that the switch system can automatically perform network loop monitoring operations on other VLANs. For example, to enable the switch to perform network loop monitoring on all VLANs of the Hybrid port and the Trunk port under the Ethernet 16 port, perform the following Configuration:

First switch to System View Mode, then enter Ethernet port 16 view, at the H3C-GigabitEthernet1/0/16 command line prompt, enter the string command "loopback-detection per-vlan enable" and click the Enter key. Then, the switch system can perform network loop monitoring in all VLANs to which the Hybrid and Trunk ports belong. Of course, after all the preceding string commands are executed successfully, we also need to use the "quit" command to exit the System View status of the switch, and then run the "save" command, you can save the port configuration parameters of a vswitch. Otherwise, all the previous configuration operations will be automatically lost when the vswitch is restarted once in the future.

Control Network loop monitoring status

Sometimes, before enabling the loop monitoring function of a switching port, we need to check the loop monitoring status of the corresponding port, if you find that the loopback monitoring function of the corresponding port is already running, you do not need to execute the "loopback-detection enable" string command again. When viewing the monitoring status of a specific Ethernet port, we can first switch to the view mode of the specific Ethernet port of the switch according to the previous operation, then execute the string command "display loopback-detection" in the corresponding view State. On the displayed page, we can see whether the network loop monitoring function of the specified switch port is enabled, if "Loopback-detection is running" is displayed on the result page, the network loop monitoring function of the corresponding switch port is enabled successfully. Of course, from this result interface, we can also see other monitoring parameters, such as the time interval of network loop monitoring and the results of network loop monitoring; in other words, if there is a network loop switch fault in the LAN, we can see from here which switch port has a network loop phenomenon, at this time, the network administrator can check the target switch port based on the monitoring results, which can greatly improve the efficiency of solving the fault of the network loop switch.

In the future, when we want to disable the network loop monitoring function of a vswitch, we only need to switch the vswitch background management interface to the System View Mode, execute the "undo loopback-detection" string command at the command line prompt in this status, so that all ports in the switch will be automatically disabled for network loop monitoring.

Network loop faults

After the network loop monitoring function of a vswitch is enabled, how can we use the monitoring results to quickly solve the problem of network congestion caused by the network loop? In fact, the switch uses different methods for switching ports of different link types to solve network loop faults. For example, if the link type of an Ethernet port is Hybrid and Trunk, the switch system will automatically report the result of the loop monitoring to the log file. If we enable the loop monitoring control function for the corresponding port, the switching port is automatically isolated from other switching ports, so that the network loop of the corresponding port does not affect the working status of other switching ports.

If the link type of the specified Ethernet port is Access port, once the network loop monitoring function of the switch finds that the port has a network loop, the Network Administrator is automatically prompted that a switch port under a working subnet has a loop fault and the switch port is automatically disabled, at the same time, the monitoring results are reported to the system log file.

Other configuration skills

For different switching ports, we need to use different configurations to ensure that the lan network is always in an efficient running state. If we rashly enable the network loop monitoring function for the switching port, some inexplicable switch failures may occur in the LAN. For example, if an Access-type switch port is uplinked to a wide area network (WAN) or a downlink hub, you are advised not to enable the network loop monitoring function for the Access-type switch port, otherwise, once the function detects a network loop under the corresponding switch port, the switching port will be automatically disabled, in this way, the WAN or LAN connecting to or from the port will fail to access the Internet.

For several switches connected up and down through the Trunk port, as the corresponding switch port is divided into different virtual work subnet environments, we should be careful to configure the network loop monitoring status of the Trunk port, if we rashly configure this switching port as a loop monitoring controlled function, once a network loop exists under a switch port, the Trunk port will be automatically disabled, in this case, the operation status of all switches will be affected. At this point, we can try to enable the network loop monitoring function for all Trunk ports, but we cannot configure the Trunk port to an uncontrolled status. In the future, if a network loop fault occurs under a port in the LAN, the Trunk port will not be forcibly controlled and closed. Then, the network administrator must check the network loop monitoring status of the switch in time, you can quickly find the specific switch port with a loop fault, so that you can efficiently solve the network channel congestion fault.