what do you mean network nodes?
if you want to index server data, just install a universal forwarder.
if you want to index network appliances data (e.g firewall, LB, etc) depending on the vendor/tech most likely you'll be using syslog to send data to Splunk.
if you want to get data from DBs, just install Splunk DB Connect.
if you want to get wire data, just use Splunk Stream.
Hope I was able to help you. If so, some karma would be appreciated.