Summary
There are three URL's defined in the discagnt.ini file and UD agent uses these URL's in sequence if there is failure of primary URL.
Question
UD Agent configuration file discagnt.ini file contains the three URL values and it is being used in sequence.
The PrmaryIp and secondaryIp correspond to URL1 and URL2.
The URL's are used in sequence by the UD agent, when it finds one of the URL is failed.
Answer
When callhome happens, the order of the URL is as below.
URL1 -> URL2 -> URL0.