mastername.salesforce.com has no SRV records.
Question and response
Question
dig mastername.salesforce.com. SRV
Answer
The response has no answer records.
Authority
salesforce.com. 1800 SOA mastername.salesforce.com. hostmaster.salesforce.com. 2016655394 600 900 2592000 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0