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