When I connect the VPN(L2TP), it connect success and any thing is fine,
but when I idle some time or sleep mac
when I connect VPN again, the VPN status still show connect success
but it is no effect
also I can't ping to the server either.
In order to resolve this question
I must to reboot my mac
when I restart the mac.
every will fine again
so, How can I reset some net setting(like restart) to resolve this question
for your reference, I've found the solution
try Network -> [your net] -> Advanced -> Tick "Send all traffic over VPN connection"