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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. (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 CHAN 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 CHAN 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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