HP Procurve Switch Loop

Even in a medium-sized local network, encountering Loop (cyclic error) problem is a situation that a Network administrator does not want to encounter at all. However, it is possible to prevent such fatal errors with simple but useful methods.

Loop Detection

There are two most known methods to prevent loop failure. The first is the Spaning Tree method and the second is the Loop Detect method. We will cover the Spaning Tree method in our upcoming articles. But for now, we will try to prevent the error from occurring with the Loop Detect procedure.

If you want, you can experiment with a switch that you do not use and keep in reserve to see the result. In order to understand the results more clearly, let’s turn on our switch and connect from the console with telnet.

Loop Protection

Let’s come to the Config screen and return our switch to factory settings with the“erase startup-config” command. In this way, we will remove any configurations that may exist on it.

When the switch restarts, let’s go to the config line again and write the following two lines of code.

loop protect 1-48
loop protect disable-timer 300

The first line defines which ports will be loop detected. Writing 1-48 means that it detects all ports from 1 to 48.

In the second line, the time in seconds is set to disable the port in case the possible loop detection is a temporary situation. The 300 parameter here specifies that the port or ports that fall into the loop after 300 seconds will be disabled.

Before applying the method written in our article on the switch we emptied for trial purposes, let’s connect both ends of a single patch cable to the same switch and see how the status loop event develops step by step by following the CPU usage percentage. The CPU will be maximized in a short time.

Before reaching the top level, that is, before the switch is locked, let’s apply the loop detect commands as above. As soon as you press Enter, you will see that the link lamps on the two ports that cause the loop are extinguished and passivated.

We will discuss more about Spaning Tree Protocol (STP), one of the effective methods, in our upcoming articles. You can find detailed information about Spaning Tree in our article titled Spaning Tree Configuration in Procurve Switches.

That’s all for now. If you encounter problems while trying it out, be sure to leave a comment on this article. I will try to help you.