The 50,000–59,999 Port Range

The final NAT caveat centers around the TCP/UDP 50,000–59,999 port range that was required to be open to A/V Edge IP addresses in Office Communications Server 2007. This requirement was removed in Office Communications Server 2007 R2, which introduced the capability for Edge Servers to relay media between each other, but since it was not possible to use NAT with multiple Edge Servers back then, it did not cause any issues.

Since Lync Server 2010 and 2013 both support NAT for Edge pools with multiple servers, there is an additional wrinkle to the inbound firewall rules that must be considered. Imagine a scenario in which an organization has two Edge Servers in a single Edge Server pool, both using NAT for the A/V Edge ...

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