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

Warren Kumari warren at
Mon Jun 4 15:28:49 UTC 2018

On Mon, Jun 4, 2018 at 8:20 AM Ict Security < at>

> 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!

​This sounds suspiciously like ​conntrack (or some other state / connection
tracking) becoming full.

Depnding on OS / version, does:
conntrack -L
cat /proc/net/ip_conntrack
produce a lot of output?

Are you running iptables / ipfw / <similar>? Behind a firewall? Are there
any interesting messages in [/var/log/message|/var/log/syslog/|<wherever
you have BIND logging>] ?


> 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
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I don't think the execution is relevant when it was obviously a bad idea in
the first place.
This is like putting rabid weasels in your pants, and later expressing
regret at having chosen those particular rabid weasels and that pair of
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