How To Clear the ARP Cache

The ARP cache acts as a library of mostly dynamic ARP entries. These are usually made when IP addresses are resolved from a hostname and then into a MAC address. This process is what allows your system to properly communicate with an IP address.

Clearing the ARP cache is not always needed. In fact, in most cases rebooting the switch or the router is more than enough to fix any latency or connection issues. Clearing the ARP cache essentially causes all the requests in your database to go through the entire ARP process again.

Basically, every connection you now establish will have to resolve the MAC address from the IP address again.

However, over time an ARP cache can become damaged. ARP cache entries become stale and new additions to the database might not always override expired entries in your collection.

When this happens, you’ll often get errors that affect the system and the network’s performance.

Two common signs that your ARP cache might need clearing are if you can’t load various websites that used to work well and if you can’t ping certain IP addresses when you know those sites are functioning properly.

Windows

If you’re the point and click type, you can use the Control Panel to clear the ARP cache. Here are the steps to do so.

1. Locate and access Control Panel
2. Pick the Administrative Tools menu
3. Click on the Computer Management menu
4. Locate and access Services and Applications
5. Scroll down until you find the Routing and Remote Services icon and access it
6. Use the drop-down menu to select Disabled and click OK
7. Restart your system
8. Go back to step 6 and select Enable this time and click OK

You don’t have to restart your system again after this.

Of course, the simplest method involves typing a simple command line. The first thing you have to do is to locate and open the Command Prompt window. You can do this by manually clicking the Start button or pressing the Windows button on your keyboard.

From there you want to type ‘cmd’ in the Windows Start Search box. You have to do this for all Windows versions after Vista.

If you’re on the administrator account, just click the cmd icon or press enter. If you’re not on the administrator account, you might have to right-click and choose run as administrator in order for the NetShell command to work.

You can also force administrator privileges if you press Ctrl-Shift-Enter and select the cmd icon.

After the Command Prompt window opens, you have to type in the following command line:

netsh interface IP delete arpcache

It should look something like this

Press enter and give it a few seconds to run its course.

Linux

Clearing the ARP cache in Linux is somewhat similar. Instead of using the Windows Command Prompt you’ll have to open a terminal prompt. Then you’ll have to become root on your system.

Once that’s done you run the following commands in sequence:

arp –n

This line allows you to view your ARP cache. It will let you know if it needs a refresh or not.

ip –s –s neigh flush all

This command is used to clear the ARP cache.

arp –n

By using this command again, you validate the results. You’ll also be able to compare the pre-clear list with the post-clear results and make better sense of what was wrong with your system.