Q: What firewall ports should we open to make IPSec work through our firewalls?

A: To make IPSec work through your firewalls, you should open UDP port 500 and permit IP protocol numbers 50 and 51 on both inbound and outbound firewall filters. UDP Port 500 should be opened to allow Internet Security Association and Key Management Protocol (ISAKMP) traffic to be forwarded through your firewalls. IP protocol ID 50 should be set to allow IPSec Encapsulating Security Protocol (ESP) traffic to be forwarded. Finally, IP protocol ID 51 should be set to allow Authentication Header (AH) traffic to be forwarded.