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Occasionally, I noticed a lot of following messsages in syslog

Nov {datetime} hostname kernel: [8226528.586232] AIF:PRIV TCP packet: IN=eth0 OUT= MAC={mac} SRC={sourceip} DST={destinationip} LEN=60 TOS=0x00 PREC=0x00 TTL=63 ID=20361 DF PROTO=TCP SPT=39950 DPT=37 WINDOW=14600 RES=0x00 SYN URGP=0

On the Internet, I found that DOS attack may cause such type of output, unfortunately, I don't understand what does this log mean. The only thing is clear for me is this log is related to network.

The source host is the host where nagios is installed.

Does it mean nagios somehow does behave well?

And what does it mean at all?

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Lines like this are logged by netfilter if you have iptables rules that have the LOG target and those are triggered. To see your iptables rules, use iptables -L -v -n

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Thank you very much for pointing this out, for adjusting iptables settings I use arno-firewall, do you know what is the fast way to identify what's rule is blocking, and in general how to solve this problem – com Nov 11 '12 at 16:05

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