You can use the TCP Ping utility to determine network latency between two instances. See this for more details
yum install tcptraceroutecd /home/usernamewget http://www.vdberg.org/~richard/tcppingchmod 755 tcpping./tcpping 192.25.26.27 4503
To clean up, delete TCP Ping with rm -rf tcpping and uninstall TCP TraceRoute with yum remove tcptraceroute