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

[Klaus Darilion]

Am 04.06.2018 um 14:20 schrieb 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!

Just a shot in the dark: I guess Bind opens multiple sockets, one for 
each IP address. Every socket has its own receive-buffer. Under heavy 
load, the receive buffer gets full and you have packet loss. So your 
client send retransmissions and sometimes the packet goes through and 
you receive an answer (high delay)

When you query the other IP, the socket is idle, hence no full buffers 
and your query gets received and processed immediately.

Checking the state of the receive buffer can be done with netstat, and 
packet loss due to full receive buffer can be seens in the "dropped 
packets" of the respective interface.

regards
Klaus