[strongSwan] VPN Performance over WAN (jitter)

[Mirko Parthey]

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?

What type of system are your VPN routers? For example, an embedded system
running OpenWrt/LEDE, or a PC running a standard Linux distribution.

Do your VPN routers use a bandwidth limiter (shaper), such as HTB or
Cake?

Regards,
Mirko