Slow reply under heavy load (on a specific NIC ip)

[Ict Security]

Hi guys,

we are running a Bind 9.x Server, everything is going fine.
Under particular heavy load mometns, with some hundreds of concurrent
queries coming in, sometime Bing stops answering for some seconds or
answer with important delays.

But, when i try to query the same server/same Bind on a NIC alias IP
during congestion on the main IP, everything is fast!

I changed some tunings in:
max-connections in /proc
txqueue in network
ipv4_ports

and i mitigate something.
But it is not completely solved.

Do you think Bind could have some NIC IP limit?
Some ideas?

Really thank you!
Francesco