Switch Port Analyzer (SPAN)


Network monitoring is an essential part of maintaining a healthy and secure network. One critical tool for network monitoring is Switch Port Analyzer (SPAN).

SPAN allows administrators to monitor and analyze network traffic by providing a copy of the traffic to an analysis device without interrupting the flow of data. In this article, we will provide an in−depth examination of SPAN, including its definition, significance in network monitoring, setup procedures and best practices, use cases, advanced features, limitations, and alternatives.

Understanding SPAN

Switch Port Analyzer (SPAN) is a feature available on modern network switches that allows you to monitor network traffic by copying data packets from one or more source ports to a destination port. The destination port is typically connected to a monitoring device, such as a packet analyzer or intrusion detection system, which can then analyze the copied packets for troubleshooting, performance monitoring or security analysis purposes.

How SPAN works

When a switch receives data packets from a source port that is configured with SPAN, it copies those packets and forwards them to the destination port, which receives and processes them independently from other traffic on the network. This process is done in real−time and does not impact the delivery of original traffic across the network.

Types of SPAN ports

There are two types of SPAN ports:

Source Port: This is the port where you want to copy data from. You can select one or multiple source ports for each SPAN session.

Destination Port: This is where you want to send the copied data for analysis. You can use any available unused physical port on your switch as the destination port.

Advantages and disadvantages of using SPAN


  • Saves cost since it does not require additional hardware like TAPs.

  • Easily set up by IT professionals without special training.

  • Able to capture traffic at wire speed in real−time without latency.


  • The switch's CPU may become overtaxed under heavy usage leading to dropped packets.

  • Certain switches may have limits on how many sessions they support concurrently.

  • Sensitive information could be lost if not properly configured for security measures like encryption during transport across networks.

Overall, SPAN is an essential feature that allows network administrators to monitor and troubleshoot their networks effectively. By understanding how SPAN works, the types of ports used, and the advantages and disadvantages of using SPAN in network monitoring, you can make informed decisions when configuring your network devices.

Setting up SPAN

Switch Port Analyzer (SPAN) is a powerful tool for network monitoring, but to use it effectively, you need to set it up correctly. In this section, we'll cover the basics of configuring SPAN ports and provide some best practices for getting the most out of your SPAN setup.

Configuring a source port

The first step in setting up SPAN is to choose the source port(s) that you want to monitor. A source port is any switch port that carries traffic that you want to monitor. Typically, this includes ports that are connected to mission−critical devices such as servers or routers.

Configuring a destination port

Once you've configured one or more source ports for SPAN monitoring, you need to choose a destination port where all of the monitored traffic will be sent. This can be any switch port that is not already being used by an active device.

To configure a destination port for SPAN, simply enter another set of CLI commands. Again, the specific commands will vary depending on your switch model and firmware version.

Best practices for Setting up SPAN

When setting up SPAN on your network, there are several best practices that can help ensure that your monitoring is effective and reliable: − Use dedicated hardware: Whenever possible, use dedicated hardware specifically designed for network monitoring tasks.

This can include specialized switches or network TAPs (Test Access Points). − Minimize latency: To ensure accurate monitoring, it's important to minimize the latency (delay) between the source and destination ports.

Use cases for SPAN

Troubleshooting network issues

One of the primary use cases for SPAN is to troubleshoot network issues. When a user experiences poor network performance, it can be difficult to determine the root cause of the problem.

With SPAN, administrators can easily monitor the traffic on specific ports and identify any anomalies or errors that may be affecting network performance. By capturing and analyzing packets in realtime, administrators can quickly identify and resolve issues before they impact users.

Monitoring network traffic

Another important use case for SPAN is monitoring network traffic. Administrators can use SPAN to capture and analyze data flow on specific ports to gain insight into how the network is being used. This information can then be used to optimize network performance, detect potential security threats, and identify areas where bandwidth usage could be reduced.

Analyzing security threats

SPAN also plays a crucial role in security monitoring by allowing administrators to detect and analyze potential threats on the network. By configuring a SPAN port to monitor traffic on critical resources such as servers or gateways, administrators can capture all incoming and outgoing packets in realtime. This data can then be analyzed for signs of suspicious activity such as malware infections or unauthorized access attempts.

Overall, Switch Port Analyzer (SPAN) provides invaluable visibility into network traffic that is critical for troubleshooting issues, optimizing performance, and detecting security threats. Its ability to capture packets in real−time provides an unparalleled level of insight that would be difficult if not impossible to obtain otherwise.

Advanced Features of SPAN

The Switch Port Analyzer (SPAN) feature is a powerful tool for network administrators to monitor and analyze traffic on their network. In addition to the basic functionality, advanced features are also available that can improve the overall monitoring capability of SPAN.

Remote Monitoring with RSPAN

RSPAN allows network administrators to remotely monitor network traffic from a different VLAN or switch. This feature extends the reach of SPAN beyond local switches and enables monitoring across multiple switches in a distributed environment. By using RSPAN, network administrators can capture traffic on source ports from different locations and forward it to a destination port for analysis without physically being present at those locations.

Using Multiple Source Ports with ERSPAN

The Encapsulated Remote Switched Port Analyzer (ERSPAN) feature extends the capabilities of SPAN by allowing multiple source ports to be monitored simultaneously. Unlike regular SPAN sessions which only allow a single source port per session, ERSPAN enables administrators to create more granular monitoring sessions by capturing traffic from multiple source ports across different switches or locations into one single destination port.

Combining Multiple Switches with VSPAN

The VLAN−based Spanning (VSPAN) feature enables network administrators to monitor traffic from multiple switches on a single switch location. This feature allows for the combination of SPAN sessions across multiple VLANs or switches to create a more comprehensive view of network traffic.

VSPAN offers many advantages over traditional SPAN, such as enabling monitoring at core switches without the need for additional physical access points and avoiding network congestion by offloading traffic across different devices.


The Switch Port Analyzer (SPAN) is an essential tool for network monitoring. It allows network administrators to gain insight into their networks by capturing traffic data from specific ports, which can be used for various purposes such as troubleshooting, debugging issues and analyzing security threats. With SPAN, users can view and analyze real−time network traffic without disrupting the actual flow of data.

Updated on: 11-Jul-2023


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