I installed gateway with NAT between PC and network. User of PC can chat via Lync client but can't call or join conference. What ports should be mapped via NAT for Lync client to use all Lync facilities? Updated: the question actually is about NAT port mapping of Lync client.
The following table summarizes the ports and protocols used by Skype for Business/Lync clients:
Port Protocol Notes
5061 TCP (SIP) Used for SIP/MTLS authentication of A/V users. Communications flow outbound through the internal firewall
443 TCP (HTTP) Used by Skype for Business clients/Lync connecting from outside the intranet for SIP communications
1024-65535 UDP/TCP Port range used for inbound and outbound media transfer through the external firewall
6891-6901 TCP Port range used by Skype for Business/Lync clients for file transfer
If you experience problems with Audio/Video Conferencing, media or file transfer, please verify that corresponding ports are open on your firewall.