If your firewall blocks all traffic to all non-whitelisted IPs then you can start by allowing
*.pubnub.com, *.pndsn.com, *.pubnub.net and *.pubnubapi.com.
If your firewall requires specific IP whitelisting then you must be on a paid plan.
Please, contact PubNub Support for the full list of publicly accessible inbound and outbound PubNub Network IP addresses.