This is a diagram of Splunk components and network ports that are commonly used in a Splunk Enterprise environment. Firewall rules often need to be updated to allow communication on ports 8000, 8089, 9997, 8080 and 514.
https://api.us-2.crowdstrike.com
https://firehose.us-2.crowdstrike.com
https://www.splunk.com/
https://login.splunk.com/
https://download.splunk.com
https://splunkbase.splunk.com/