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?