Morning! welcome to and thanks for checking it out. Today, I’ll write this post about Arista and how to monitor sessions mirroring traffic from an active port to a destination port.

You can analyze network traffic passing through ports or VLANs by using SPAN or RSPAN to send a copy of the traffic to another port on the switch or on another switch that has been connected to a network analyzer or other monitoring or security device. SPAN copies (or mirrors) traffic received or sent (or both) on source ports or source VLANs to a destination port for analysis. SPAN does not affect the switching of network traffic on the source ports or VLANs. You must dedicate the destination port for SPAN use. Except for traffic that is required for the SPAN or RSPAN session, destination ports do not receive or forward traffic


SPAN sessions (local or remote) allow you to monitor traffic on one or more ports, or one or more VLANs, and send the monitored traffic to one or more destination ports.

A local SPAN session is an association of a destination port with source ports or source VLANs, all on a single network device. Local SPAN does not have separate source and destination sessions. Local SPAN sessions gather a set of ingress and egress packets specified by the user and form them into a stream of SPAN data, which is directed to the destination port.

RSPAN consists of at least one RSPAN source session, an RSPAN VLAN, and at least one RSPAN destination session. You separately configure RSPAN source sessions and RSPAN destination sessions on different network devices. To configure an RSPAN source session on a device, you associate a set of source ports or source VLANs with an RSPAN VLAN. The output of this session is the stream of SPAN packets that are sent to the RSPAN VLAN. To configure an RSPAN destination session on another device, you associate the destination port with the RSPAN VLAN. The destination session collects all RSPAN VLAN traffic and sends it out the RSPAN destination port.

SPAN and RSPAN do not affect the switching of network traffic on source ports. A copy of the packets received or sent by the source interfaces are sent to the destination interface. Except for traffic that is required for the SPAN or RSPAN session, reflector ports and destination ports do not receive or forward traffic

Arista support max 5 mirror sessions, so let’s see useful commands. 

How to configure an Arista session

A session can be configured per Ethernet o per port-channel. Both commands are similar so, let my write down the steps.

In this case, we are going to mirror traffic from Port-channel 10 to Ethernet port 38. In case the destination would be a port-channel, just change Ethernet and write port-Channel

How to check pending sessions

Run the following command to see active or pending sessions 

How to commit an Arista session

Once the sessions is configured, it must be committed to save the session. 

How to abort  an Arista session

Let’s abort / cancel a pending session. 

How to check active Arista session


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