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The Virtualbox configuration is correct, yes. I use it myself on production VMs.
As I said, the issue is with your IP configuration & routing configuration, both not in scope of this forum.

noteirak wrote:The Virtualbox configuration is correct, yes. I use it myself on production VMs.
As I said, the issue is with your IP configuration & routing configuration, both not in scope of this forum.

thanks a lot for your help noteirak.
it's like you said, i still have to learn more....
by the way, i could achieve the configuration i wanted.

i found that i should change ip_forward value to '1' . though i have activate ip_forward before but still no successfull connection, maybe because i missed something.
and the routing shoudl be something like this " ip route add next_hop_network via gateway".
and the intermediate router could be configured using brideged adapter or internal network.

is it appropriate if i asked why after cloning VM, file 70-persistent-net.rules gone missing ? or should i make a new thread??
i havent's found a clue on the net.
i used this command , udevadm trigger --action=add , but it still cannot regenerated

Not sure how this file is generated in the first place, but cloning generates new Hardware ID and new MACs (unless you prohibit it).
Typically, it means your network config get reseted. I am not sure if that specific file should disapear, but you could have your network config wipped by the guest OS.

It definitly wouldn't be a Virtualbox issue tho, but most likely a consequence of the cloning.