Polycom DOC2230A - Manual (Page 53)

Chapter 3 - Initial System Configuration
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8. In the Settings dialog box, Click Next.
The DNS Settings dialog box opens.
For H.323 conferencing, DNS can be used for gatekeeper discovery
using the gatekeeper host name. Using NAT Traversal, the DNS is
queried for the NAT server IP address used for allocating the public
(external) IP addresses to the cards for the conferencing session.
For SIP conferencing, domain names are required and therefore it is
recommended to enter the details of the DNS server and the local domain
name. The DNS is also used if SIP Server discovery is applied. The
system decides whether to use the DHCP or the DNS server for
auto-discovery with preference to the DNS server.