How DNS in Message Processor Add and Reomve IPs ?

[Roaa]

I see in this documentation a problem called Connection errors due to incorrect DNS resolution

https://docs.apigee.com/api-platform/troubleshoot/runtime/503-service-unavailable#connectionerrorsdn...

There is IPs added and deleted I just want to know ,, 

Where these IPs come from? 

Why some of them are being deleted ?

Any Help ?