Basics of Port Mirroring Configuration

Port Mirroring 101

When you have an important network, it’s a common practice to use some form of network monitoring. This can help you keep an eye on things for better security and network performance.

How do you implement monitoring techniques into a network?

One of the most straightforward methods is to use port mirroring.

What Is Port Mirroring?

Port mirroring is a technique that enables traffic monitoring. Whether you’re trying to increase network security, diagnose network issues, or search for ways to improve network efficiency, monitoring is an important way to get the raw information.

As for port mirroring itself, it’s a technique that copies and sends network packets that are seen on one port to another port.

So, the monitoring port (often called the destination port) can see the exact packets that are sent to an endpoint device and inspect them. But, because the packets are mirrored, the original data still goes to the original port (source port) unimpeded. In this way, the network traffic can be analyzed without disrupting the original intended communication.

How Does Port Mirroring Work?

To set up port mirroring, you will need to configure your networking devices appropriately. There are two different ways to go about it, and they require different setups. One option is local port mirroring, which is much simpler. Remote port mirroring requires extra steps.

Both techniques will be covered individually below.

Local Port Mirroring

The name local is important to this technique. It means that everything is happening on a single switch. So, the source port is on the same networking device as the destination port.

The process is actually pretty simple. The switch receives packets for the source port. Every packet that is sent to the source port is copied and forwarded to the destination port. That’s really it.

In order to actually implement local port mirroring, you simply need to enable the feature on the networking device for the port that you want to mirror. Once complete, your monitoring device will be able to analyze traffic for your intended purpose.

Remote Port Mirroring

Remote port mirroring involves a destination and source port that are not on the same switch. Because of that, there is a necessary intermediate step that enables remote mirroring to work.

In this case, the source device is connected to a switch (or other network device). The source switch then has to connect to a secondary networking device. The source switch forwards a port to the secondary. This works on the same principle as local port mirroring. When you enable mirroring, your destination port will connect to a second networking device instead of the monitoring device.

On the second networking device, you need to forward traffic to the port being used by the monitoring device. When this is done, the setup is complete, and the remote port mirroring will work.

Common Applications

Port mirroring isn’t the most complicated monitoring technique, but it does add steps and hardware to a network. Why go through the effort?

For the most part, there are three reasons to use port mirroring for network monitoring.

The first is for network diagnostics. If you face downtime or network interruptions, your mirrored monitoring device can identify common problems very rapidly, possibly even in real-time, enabling you to remedy the situation very quickly.

A second common application is security. With port mirroring, you can inspect network packets to look for signs of intrusions, malicious software, and other security concerns.

Lastly, you can use this technique for network analysis. The monitoring device can help you identify network bottlenecks and other areas of opportunity for improving network functionality and efficiency.

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