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We have 2 VM's running on ESX 5.1. When I do a ping -A, after a while I get every second ping as a DUP!. When doing a normal ping, I get 5 or 6 DUP!s, and then it returns to normal.

Any ideas what to check?

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The man page says ping will report duplicate and damaged packets. Duplicate packets should never occur, and seem to be caused by inappropriate link-level retransmissions. Duplicates may occur in many situations and are rarely (if ever) a good sign, although the presence of low levels of duplicates may not always be cause for alarm –  schaiba Jul 23 at 13:08

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If it return something like this:

1472 bytes from core-212-23-0-100.zen.net.uk (212.23.0.100): icmp_seq=1 ttl=121 time=28.9 ms
1472 bytes from core-212-23-0-100.zen.net.uk (212.23.0.100): icmp_seq=1 ttl=121 time=30.3 ms (DUP!)

There are multiple servers providing PING:We are running 6 hosts in this specific cluster (as you said) Each one (of your hosts) is responding to the ping packet, hence the dups. It's not something bad here.

To solve the problem you can see this link:

https://github.com/sasikanthbabu/Layer3Switch/issues/14

And as schaiba mentioned:

The man page says ping will report duplicate and damaged packets. Duplicate packets should never occur, and seem to be caused by inappropriate link-level retransmissions. Duplicates may occur in many situations and are rarely (if ever) a good sign, although the presence of low levels of duplicates may not always be cause for alarm

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Hi, thanks for the quick reply, what do you meen by this "There are multiple servers providing 2 VM's running on ESX 5.1." ? We are running 6 hosts in this specific cluster. –  Dion Jul 23 at 13:16
    
@Dion sorry I thought there are 2 machines, if you have 6 hosts then it will case DUP from them,see update –  Networker Jul 23 at 13:20
    
Let me be clear, we have 6 hosts running multiple VM's. These 2 VM's cause DUP! messages when running a Ping -A to them. They both have only 1 nic, and we did a sniffer network trace, the DUP's come back from the same MAC. This only start happening after running the ping -A for a while. –  Dion Jul 23 at 13:25

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