Your ReadyNAS storage system has at least one Ethernet port. Some ReadyNAS storage systems have 1 or more additional Ethernet ports. Your ReadyNAS system has a network adapter for each of its Ethernet ports. The ReadyNAS Admin Page and the Insight app always display the adapters in the same order, regardless of which adapters are connected to other devices and which are not.
When you view your ReadyNAS system’s network adapters in the Admin Page or in the Insight app, the adapters are listed starting with eth0 for the first Ethernet port’s network adapter, then eth1, eth2, and so on. The numbering does not start over for 10-Gigabit Ethernet ports.
If the port corresponding to eth0 (or any other port) is not connected to anything, the IP address for that port is listed as 0.0.0.0. If you see an IP address for a port listed as 0.0.0.0, that port is not connected to a device.