tinc - Sep 2017 - Will couple of packets drop when in-frequent traffic go through tinc?

An very interesting test did yesterday that, LAN1 and LAN2 setup an tinc VPN
which is quite simple(the physical link between tinc nodes are quite
stable/fast), and no any application traffic to go through the tinc.

Later, I setup smokeping which LAN1 initial 20 ping to LAN2 on a per-minute
basis, but as you saw from the below picture, it had packet drop. But if I
perform a constantly ping from LAN1 and LAN2, then the smokeping output show the
packet drop no longer happens.

From this observation, it seems the tinc VPN connection will have some sort of
idle connection and will be pause, and constantly traffic will make the
connection active?

https://ibb.co/jrkF4F <https://ibb.co/jrkF4F>

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On Mon, Sep 11, 2017 at 10:58:09AM +0800, Bright Zhao wrote:
> An very interesting test did yesterday that, LAN1 and LAN2 setup an tinc
VPN which is quite simple(the physical link between tinc nodes are quite
stable/fast), and no any application traffic to go through the tinc.
> 
> Later, I setup smokeping which LAN1 initial 20 ping to LAN2 on a per-minute
basis, but as you saw from the below picture, it had packet drop. But if I
perform a constantly ping from LAN1 and LAN2, then the smokeping output show the
packet drop no longer happens.
> 
> From this observation, it seems the tinc VPN connection will have some sort
of idle connection and will be pause, and constantly traffic will make the
connection active?
Tinc doesn't keep all UDP connections alive, since in a VPN with many
nodes, this would cause a large of the amount of keepalive packets
being sent between nodes. If you don't send anything to another node for
a while, tinc might pause the UDP connection. However, if you then send
something, tinc knows the UDP connection is not alive yet, and while it
is reestablishing the UDP connection, it will send your packets via its
TCP connections. So in principle, you should not see this kind of packet
loss.

But, if the UDP connections are alive, and the real network has packet
loss, then you will see that on your VPN as well.

-- 
Met vriendelijke groet / with kind regards,
     Guus Sliepen <guus at tinc-vpn.org>
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