ngrep is a tool to grep network traffic.
Install ngrep on CentOS using yum. It is part of the EPEL repo, so please refer to EPEL repo setup.
yum -y install ngrep
Look at the traffic hitting port 8080 (common port used for java servlets like tomcat or resin)
ngrep -q -d eth0 -w byline port 8080
Look at ICMP traffic. Ping, traceroute, mtr, etc.
ngrep -q -d eth0 '.' 'icmp'
There are a lot of good regex examples for ngrep here.(Comments)