Too many connections on the same IP

[Job]

Hello,

during a massive DNS utilization our Bind 9.10.1-P1 seems not to resolve anymore, neither local zone.
We shutdown one of the two nodes and all queries arrived only on one node.

CPU and memory load were not too overloaded, machine was quite fine.

After some fast tests, i noticed that if from clients i used an ip alias of Bind server, it worked perfectly!

Only on main ip there were congestion problems, but resolving on ip aliases worked fastly!

Where was i wrong?

Thank you!
Francesco