To enable clients on the Internet to find Lync Server services, add an Address (A) record to an external DNS that is authoritative for the DNS domain that services Lync Server externally. This includes (A) or (SRV) records, as described in Chapter 11.
The procedure for creating records depends on the DNS server used. In the case of an externally hosted DNS, it might be as simple as calling your service provider and requesting the records.
Keep in mind that it might take several minutes to as much as a few hours for the new records to propagate to an external DNS server and become available to clients.
On most reverse proxy solutions, it is possible to have all external Lync Web Services ...