Cisco switch configuration problems and related usage skills

The Cisco switch launched by Cisco is also a giant in the entire industry. The Cisco switch performs well in the market. The Cisco switch will think that the wrong command is the host name, and try to resolve it by querying the DNS server.

In the process of debugging and maintaining Cisco switches, Xiangzi may encounter some headaches. Fortunately, after a period of system learning, these problems have been solved one by one. In fact, understanding these methods is very helpful for improving the efficiency of debugging vswitches. Here, we will introduce some accumulated experiences for your reference.

I. How to Prevent the system information from interfering with the command input?

I believe many network administrators and friends have encountered this problem: when debugging a Cisco switch through the CONSOLE port connected to the switch through a serial port (except for the first time configuring the switch, most of them are due to a switch failure and cannot be logged on through the network port). This is often the case of 100,000 in a rush.

However, the more urgent the system is, the more difficult it is to create a command than to log on to the system, because some system prompts will pop up from time to time (or continuously) on the configuration interface opened by the Super Terminal. At this time, command input will be completely disrupted, that is, a complete string of commands cannot be entered in one line.

At that time, it was really a test of the psychological quality of the network manager and the keyboard fingering method. You can use the command with your eyes closed to describe it. After the command is completed, you can expect this command to eliminate the error, no more error messages are displayed (of course, it is unsuccessful ). In fact, there is a way to deal with these constantly changing information. When we log on through the CONSOLE port, we only need to type 3550 # conf t.

In this way, you can effectively avoid the interference caused by commands repeatedly popped up by console messages when you enter commands. In fact, logon through the network port is also affected by system information, but this situation does not appear in the Cisco switch by default.

But it can be implemented with only one command, namely: 3550 # terminal monitor. In order to experience the actual effect, we can open two DOS windows on our PC and log on to the same Cisco switch through TELNET.

One is used for monitoring, and the other is used to perform specific operations, as shown below: for example, we execute a port shutdown and then no shutdown operation, in this case, the system information is disturbed when you want to enter the command in the first window, as shown in the following figure: 3550 (config )#.

In fact, I want to type inter fa0/4, but this command is drowned in the system prompt information. If you want to solve the problem, just type the following command: 3550 # conf t; Enter configuration commands, one per line. End with CNTL/Z. TELNET logon and CONSOLE logon. If you want to prevent the input command from being disturbed by the prompt information of the switch, you can solve the problem in the same way.

2. Do not allow the vswitch to try to use the DNS server to resolve the Host Name

What does this mean? When debugging a switch, we will inevitably enter an incorrect command, for example, if we type one more letter or one less letter, I thought the switch would prompt this command error, but a strange thing happened at this time. The system didn't prompt us for a command error, but made a connection to it (that is, the command was executed the same ), 3550 # beijing.

That is to say, the Cisco switch considers the incorrect command as the host name and tries to resolve it by querying the DNS server. If the DNS server is set on the switch, the progress will be faster. If there is no DNS server, the progress will be slow. How can we avoid this situation? Enter the following command: 3550 # conf t. After the preceding commands are executed, when an incorrect command is entered, the Cisco switch will not perform unnecessary connections for a long time.

3. quick understanding of port disconnections in vswitches

As a network administrator, when we access a new service on a vswitch, we always need to find an idle port on the Cisco switch and configure necessary services, connect the network cable, but there are many cables on the switch.

With the naked eye, it is difficult to accurately identify idle ports at once (if an error is accidentally pulled, the Network may fail). Therefore, we used to log on to the switch, run the following command: 3550 # show inter.

At this time, the switch will display the details of each port in sequence, including the port disconnection, but it is still too slow. The above three points are some of the experience accumulated by Xiangzi in learning to use Cisco switches. I hope to provide some reference to my friends and open up the fog of faults to identify the real causes of network faults.

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