See the full application note here:
http://www.digi.com/resources/documentation/digidocs/pdfs/90000640.pdf
This application note explains how to set up 2 DF1 devices on the Digi One IAP and overcome the RSLinx limitation of supporting only 1 device per IP on non-Rockwell products. The 2 devices could be 2 PLC (that is, 2 slaves) or 1 PLC and 1 HMI (that is, 1 slave & 1 master).