By default, all Cisco Meraki devices will distinguish between different clients based on their MAC address, but the MX in particular has the ability to identify clients based on IP address as well. This article outlines differences between the two options, use cases for each, as well as how to change client tracking in Dashboard.
Note: Only the MX Security Appliance has the option to track clients by IP, all other Cisco Meraki devices will only distinguish clients based on MAC address.
In many deployments, the MX security appliance is used as the gateway for the network, and performs inter-VLAN routing for the network if necessary. In this circumstance, the MX is in the same broadcast domain as all clients in the network, so the client's MAC address will be found in all traffic seen by the MX.
The following diagram outlines how the MX can see client MAC addresses in this topology:
In some cases, the MX may not be in the same broadcast domain as all clients. Most commonly, this will occur if there is a layer-3 switch performing inter-VLAN routing downstream of the MX. Since layer-3 devices will modify the source MAC address of client traffic, the MX cannot identify clients by their MAC as shown below:
In order to identify clients downstream of the layer-3 switch, the MX can be switched to track clients by their IP. Since the layer-3 switch won't be modifying the source IP of client traffic, the MX can identify different clients by IP:
When an MX is set to track clients by IP, the client MAC addresses displayed on the Clients List may not be accurate.
By default, the MX will track clients based on their MAC addresses. However, depending on where the MX lies in the network topology (as outlined above), tracking clients by IP may be necessary for client identification.
Note: The MX cannot correlate clients tracked by one method with clients tracked by the other method. As such, when changing from one tracking method to another, the MX's client list may retain the old client entries for up to 30 days, resulting in duplicate entries with different client details. It is recommended to reference these old entries for historical purposes.
Note: Track by IP is not currently supported in combined networks.
The following instructions outline how to change the client tracking method: