[strongSwan] VPN Performance over WAN (jitter)

Christian Hanster christian-hanster at gmx.de
Fri May 12 11:52:52 CEST 2017

Hi Mirko,

thanks for your response. 
> On 11 May 2017, at 20:59, Mirko Parthey <mirko.parthey at web.de <mailto:mirko.parthey at web.de>> wrote:
> On Thu, May 11, 2017 at 04:00:17PM +0200, Christian Hanster wrote:
>> Hi all,
>> at the moment I’m trying to optimize the network performance in a site-to-site
>> setup (see config below). The connection is structured as follows 
>> <network A> <—> VPN-Router A <—> Internet (WAN) <—> VPN-Router B <—> <network
>> b>
>> The problem is that the network performance between networks a and b is only
>> around 45 MBit (iperf tcp test) although the WAN connection has nearly 100MBit.
>> So I monitored the network interfaces of the routers and what I could see was
>> that there are only flowing around 48 MBit. To test if it is a performance
>> problem of the routers, I then connected the routers directly (through lan)
>> with each other and limited the network card to 100 MBit. Then the
>> VPN-performance is around 94 MBit. So the router performance is not the
>> problem.
>> Then I simulate a varying delay in the network cards and this seems to be the
>> problem because when I make a ping between the two networks over vpn and
>> internet latency is around 70ms (30ms deviation). The two servers have ping
>> times around 32ms (3ms deviations). With varying delay activated the simulated
>> throughput is only around 55MBit. My question is now if there is any tuning
>> possibility in strongswan to deal with this varying latency. 
> Hello Christian,
> I would suggest to leave your simulation aside for now.
> Did you measure the throughput between your networks without VPN?

I measured connection speed without VPN and it is nearly 92 MBit/s Down and 10MBit/s upstream from the limiting side. So the connection between the two routers does not seem to be a problem. 

> What type of system are your VPN routers? For example, an embedded system
> running OpenWrt/LEDE, or a PC running a standard Linux distribution.
I’m using two Routers based on AMD embedded series running Ubuntu x64. The CPU should not be the limiting factor as the performance between two devices directly is nearly at 150 MBit/s. 

> Do your VPN routers use a bandwidth limiter (shaper), such as HTB or
> Cake?
There are no bandwidth limiters installed. In my simulations I limited the bandwidth directly on the interface with ethtool. But in normal environment there are no limitations. 

Kind regards 

> Regards,
> Mirko
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