psd match false positives?

psd match false positives?

[afshin lamei]

hi all,
I am using the "port scan match" with its default values, my rules are like
this:
iptables -A INPUT -m psd -j LOG --log-prefix "port scan:" // log the port
scan
iptables -A INPUT -m psd -j DROP // Drop it silently

one of my DNS servers is 4.2.2.4 <http://4.2.2.4> , and I'm seeing these
logs, which say the 4.2.2.4 <http://4.2.2.4> is port scanning my box
(external interface: 192.168.100.151 <http://192.168.100.151>) !!

Oct 3 17:23:35 kernel: Port scan:IN=eth0 OUT= SRC=4.2.2.4 <http://4.2.2.4>DST=
192.168.100.151 <http://192.168.100.151> LEN=8 PROTO=UDP SPT=53 DPT=32769
Oct 3 17:23:35 kernel: Port scan:IN=eth0 OUT= SRC=4.2.2.4 <http://4.2.2.4>DST=
192.168.100.151 <http://192.168.100.151> LEN=1 PROTO=UDP SPT=53 DPT=32761
Oct 3 17:23:35 kernel: Port scan:IN=eth0 OUT= SRC=4.2.2.4 <http://4.2.2.4>DST=
192.168.100.151 <http://192.168.100.151> LEN=1 PROTO=UDP SPT=53 DPT=32773
Oct 3 17:23:35 kernel: Port scan:IN=eth0 OUT= SRC=4.2.2.4 <http://4.2.2.4>DST=
192.168.100.151 <http://192.168.100.151> LEN=1 PROTO=UDP SPT=53 DPT=32775
Oct 3 17:23:35 kernel: Port scan:IN=eth0 OUT= SRC=4.2.2.4 <http://4.2.2.4>DST=
192.168.100.151 <http://192.168.100.151> LEN=1 PROTO=UDP SPT=53 DPT=32780

It seems to be a false positive, isn't it? if so, dropping them will cause
problems, so what should i do?
regards,
afshin