[CentOS] rsyslog server cannot get the logs

I have an rsyslog server which is running Debian Stable,
and its version of rsyslog is 4.6.4-2.

All of my Debian Stable server can send log to it now.
and run both
nc $IP $PORT <<< "HELLO"
and
echo "HELLO" | nc $IP $PORT
on client, I can get log on the server.

While for my CentOS 5.7 server,
nc $IP $PORT <<< "HELLO"
works well, but
echo "HELLO" | nc $IP $PORT
can not work.
tcpdump shows that it can get both of the 2 "HELLO"
from server.

And I can not get log both by log file or tcpdump.

*.* @@IP:PORT