As you didn't mention that how those devices are ingesting data into Splunk, if they are ingesting data directly in splunk you can look at below configuration for various Data Inputs in inputs.conf
For example: For Splunk TCP Input default configuration is IP but for TCP input default configuration is dns
connection_host = [ip|dns|none]
* For splunktcp, the 'host' or 'connection_host' will be used if the remote
Splunk instance does not set a host, or if the host is set to
* "ip" sets the host to the IP address of the system sending the data.
* "dns" sets the host to the reverse DNS entry for the IP address of the system
sending the data.
* "none" leaves the host as specified in inputs.conf, typically the splunk
* Default: "ip".