Znet2.5 refers to the type of firmware that is installed on the XBee module. The XBee S2 hardware (Non B or C) support both Proprietary Znet 2.5 and ZB or Zigbee mesh firmware versions. The XBee S2B only supports the ZB or Zigbee versions and the S2C has three different versions and protocols it supports. Zigbee (ZB), Digi Mesh 2.4 and 802.15.4. That is depending on what firmware version is installed. So as long as all of your S2 hardware uses the XBee ZB function sets, they will all talk to each other.