My TN Connection

In this edition of our Switch Sense series, which examines Ethernet switching features and functions, we’ll be taking an in-depth look at Port Mirroring and it’s affect on network traffic analysis.

Port Mirroring

Network administrators often need to have a way of monitoring network traffic. One of the ways in which to do this is through Port Mirroring. Although Port Mirroring is not an IEEE standard it is a function that is found in most managed Ethernet switches today.

To use Port Mirroring a network administrator must specify which port(s) will have their traffic copied to the mirror port on the switch. The network administrator must select at least one source port to use Port Mirroring. The traffic on the source port(s) will be copied to the destination port.

A protocol analyzer is used on the port that receives the copy of the data. Traffic can be captured and analyzed without affecting normal operation of the switch. Port mirroring can also be managed locally or remotely which makes it an effective tool for network administrators to use when troubleshooting.

In this diagram there are three (3) source ports that are being monitored by the monitoring PC attached to the destination (mirror) port.

Some common terms used in configuring Port Mirroring are as follows:

• Destination Port: There is only one port that can be selected as the destination (mirror) port for monitoring traffic from the source port(s). The destination (mirror) port is where the protocol analyzer will be placed to capture and analyze the traffic.

• Source Port: Source port(s) are the ports the network administrator wants to monitor. All monitored port traffic will be copied to the destination (mirror) port. Network administrators can select multiple source ports and if they want to copy RX, TX or both RX and TX to the destination (mirror) port.

See the full line of MILAN managed switches that contain full port mirroring capabilities.

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