Running phpvirtualbox VMs and experiencing DUP! packets when pinging

[aftershocks]

I've created 2 VMs within phpvirtualbox running on xpenology (package center). When I try and ping an IP from within the VM, I get the following:

 

user@devvm:~# ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=117 time=12.0 ms
64 bytes from 8.8.8.8: icmp_seq=1 ttl=116 time=12.2 ms (DUP!)
64 bytes from 8.8.8.8: icmp_seq=1 ttl=117 time=17.7 ms (DUP!)
64 bytes from 8.8.8.8: icmp_seq=1 ttl=116 time=17.9 ms (DUP!)
^C
--- 8.8.8.8 ping statistics ---
1 packets transmitted, 1 received, +3 duplicates, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 12.012/14.974/17.925/2.857 ms

 

If I shutdown one of the VMs and re-run the ping, I get less duplicate packet so I know the virtualization is causing some issue. How do I fix this?

 

Thanks.