Solving switch faults to improve network efficiency (1)

How to quickly resolve switch faults and effectively improve network efficiency. Please refer to this article for details:

1. Solve the trouble of resetting VLAN

When managing and maintaining a LAN, if the cascade port connecting to a common switch changes, the VLAN previously configured in the switch system may not work normally. In this case, do we have to re-divide and set VLANs? If this is the case, the network maintenance workload is obviously huge. In fact, after changing the cascade ports of a common switch, we only need to enter the backend management interface of the switch, modify the working mode of the cascade port so that all VLAN access can be passed. In this way, you can avoid resetting VLAN operations. Now we will take the LAN of a certain unit as an example to introduce the specific configuration steps of the switch to you:

Assume that there are 6 VLANs in the LAN of the Organization, where S1 switches are located in subnet A and S2 switches are located in subnet B. Recently, the organization has purchased several workstations, now we need to move the S1 switch to the subnet B. Previously, the S1 switch was directly connected to the core switch of the local area network with an optical fiber cable on port 24. To avoid VLAN division in the switch system, we can change the port operating mode of the S1 and S2 switches. For example, we can first check the port settings of the S1 switch. During this check, we can remotely log on to the background management interface of the switch using the telnet command, run the "display interfaces" string command to check the specific configurations of each port of the vswitch. From the results returned by the preceding command, we can see that port 26 of the S1 switch that maintains a cascade relationship with the S2 switch is in the "interface ethernet0/26, port access vlan 2" status ", in this status, we can easily understand that the S1 switch only belongs to VLAN2. That is to say, the switch only allows the workstation from VLAN2 to pass through, and the workstation in other VLANs cannot pass through. When the S1 switch changes its placement position, it will certainly be located in the new VLAN. To make all workstations in the new VLAN accessible, we need to change the port 26 working mode of the S1 switch to "trunk" here ", in this way, the S1 switch does not need to re-divide and set VLAN, so that all workstations in the new VLAN can pass through.

Many users may wonder why the S1 switch can communicate with the lan network normally before? The original S1 switch was previously connected to the core switch of the Unit through an optical fiber cable. The working mode of the optical fiber connection port has been set to "trunk". When the placement position of the S1 switch changes, because the optical fiber cable is not used to connect to the switch, the corresponding Optical Fiber Connection port does not work.

When modifying the operating mode of port 26 of the S1 switch, we can remotely log on to the backend management interface of the switch, and execute the string command "system" in the command line of the interface ", switch the operating status of the S1 switch to the system configuration status, and then run the "interface ethernet 0/26" command to enter the port configuration status of the S1 switch No. 26th, then, enter the string command "port link-type trunk" in this status and click the Enter key. Then, the operating mode of port 26 on the S1 switch is changed to the "trunk" type; to allow all VLANs in the LAN to access the S1 switch through this port, we also need to execute the string command "port trunk permit VLAN all ", this allows you to specify port 26 to allow workstation access from all VLANs. In the same way, we can modify the cascade port mode of the S2 switch to ensure that all workstations in the LAN can access the S2 switch.

2. Solve host failure Ping failure

When managing and maintaining networks, we often perform Ping command tests on the IP addresses of a host in the LAN on the vswitch, during the test, if the IP address of the target host cannot be pinged, how can we solve the problem? When we confirm that the target host has been powered on and the system is operating normally, we can perform the following troubleshooting operations in the switch:

First, use the telnet command to log on to the background management interface of the target switch, and execute the string command "display interfaces" in the command line of the interface ", check whether the IP address of the port connecting the target host and the local switch is in the same CIDR block from the pop-up interface, or check whether the working mode of the specified connection port of the local switch is "trunk". If these parameters are not set correctly, we must modify them in time.

Second, execute the string command "display arp" and carefully check whether the content of the ARP table for Local Switch management and maintenance is set correctly from the pop-up result interface. Once an incorrect record or entry is found, it must be modified in time.

Then, check the virtual subnet in which the communication port of the local switch connects to the target host. Find the corresponding virtual subnet and check whether the VLAN communication interface is correctly configured for the virtual subnet, if it is already configured, check whether the IP address of the VLAN communication interface is in the same working subnet as the IP address of the target host. If the configuration is incorrect, must be modified in time.

If the preceding configuration parameters are normal and the Local Switch cannot Ping the target host address in the LAN, enable the ARP debugging switch in the local switch system, in order to check in detail whether the local switch can correctly send ARP packets and receive ARP packets, if the local switch can only send ARP packets but cannot receive ARP packets from outside, the cause of the failure is probably the physical link layer of Ethernet. At this time, we need to focus on the physical link layer check.