R: Too many connections on the same IP

[Job]

Hello Stefan, and thank you for the reply.

>>Are you using iptables Firewall?
>>Does the problem only occur on UDP connections to the problematic IP? Or also on TCP >>connections to the same IP?

At the beginning, i thought was an iptables-behind-firewall problem and i made massive dns resolutions locally, from the same lan where the dns server is located.
Same results: after 300/400 query per second bind make difficult to respond on the first IP.

But resolving on the secondary, alias ip, works perfectly!
What a matter!!

Thank you
Francesco