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I have the following situation, which appeared suddenly originally I can ping outside website very well, but now each VM cannot even ping its neighbor.

https://dl.dropboxusercontent.com/u/46163331/Capture.JPG (The link is the ifconfig caption)

Should there have any else tools are helpful for trouble shooting? I am really new to Linux. The best I can do is figure out all the ping packets goes into loopback interface directly@@

Thanks in advance!!!

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Which virtualization software do you use ? Did you clone each VM ? Did you change mac address of each VM ? Did you set interface in promiscuous mode ? –  Yohann May 7 '13 at 3:50
Thanks for the suggestion. I use vSphere Client, didn't clone and don't know the reason for clonning :P just try to changed the MAC address and set to promiscuous mode. but doesn't help @@ –  Gabriel May 7 '13 at 4:13
I am wondering whether there is a chance of the problem is on the switch. I don't know whether is the switch cannot accept the packets or problem on CentOS –  Gabriel May 7 '13 at 4:16
Your need to provide more information. What is the output of route -n? What is each VM's IP address? Are the VM's bridged to the LAN or using NAT? –  Matt May 7 '13 at 4:43
What is the error message when you ping? Can you try traceroute? Can you ping from a non VM machine? Is your firewall on? –  ponsfonze May 7 '13 at 4:45

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