gridmaster.telefonica.com.sv has no CNAME records.
Question and response
Question
dig gridmaster.telefonica.com.sv. NS
Answer
The response has no answer records.
Authority
telefonica.com.sv. 1848 SOA gridmaster.telefonica.com.sv. root.telefonica-ca.net. 2022110466 3600 3600 3600 3600
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0