An engineer is configuring a SIP profile for Cisco VCS SIP trunk on Cisco Unified Communications Manager and enables the option "Use Fully Qualified Domain Name" in SIP Requests. Which result is achieved by enabling this option?
A. Resolve FQDN using DNS type SRV record.
B. Resolve FQDN using DNS type A record.
C. Ensure FQDN is used in SIP Identity header.
D. Ensure FQDN is used in SIP Request header.
I agree with answer C.
C is correct
https://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/10_0_1/ccmcfg/CUCM_BK_C95ABA82_00_admin-guide-100/CUCM_BK_C95ABA82_00_admin-guide-100_chapter_01010001.html