IP addresses are assigned with the help of DHCP. In most cases mobile device receives IP address 169.254.2.1 and network interface on Mac computer gets IP 169.254.2.2.
If you choose to use a third party firewall software instead of the standard Application Firewall in Mac OS, we would recommend you to adjust the following settings for this firewall:
- Allow all in and out UDP traffic to subnetwork 169.254.0.0/16 for port 5679
- Allow all in and out TCP traffic for port 990 from subnetwork 169.254.0.0/16
- Allow all in and out TCP traffic for port 5721 from subnetwork 169.254.0.0/16
You may also check this article about TCP ports required by ActiveSync.