how to capture traffic between VM in Cloudstack

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Hi Team,

   I have a problem that how to capture traffic between VM in Cloudstack 
enviroument.Below is my test enviroument(some VM in some project):

                     ___ VM01A
                     |  
prj01A------VR
                     |___ VM02A
                     |
                     |___ VM03A

                     ___ VM01B
                     |  
prj02B------VR
                     |___ VM02B

   I need to capture traffic from prj02B-VM02B to prj01A-VM01A,from VM03A to 
VM01A.When use "tcpdump -vv -i eth0" or "tcpdump -vv -i eth2" in VR,there is 
nothing captured.Where to capture these traffic?