The Zebra P1112640-015 Ethernet module adds wired network connectivity to compatible ZD421 printers. It is listed as an accessory for the ZD421d and ZD421d-HC, making it a practical option for connecting those label printers to an Ethernet network.
The module supports Ethernet 10/100. Zebra identifies it as an Ethernet module, separate from the serial and Wi-Fi modules in the ZD421 parts list, so it provides a wired networking option for printer use.