netdev - Re: Random packet loss using IPsec with AES128-SHA1

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Date:	Wed, 16 Dec 2015 10:59:54 +0100
From:	Steffen Klassert <steffen.klassert@...unet.com>
To:	Gabriele Beltrame <belgab@...source.net>
CC:	<netdev@...r.kernel.org>
Subject: Re: Random packet loss using IPsec with AES128-SHA1

On Wed, Dec 16, 2015 at 10:17:54AM +0100, Gabriele Beltrame wrote:
> Hi,
> 
> I'm running a few Strongswan 5.3.* CentOS (Kernel 3.16.7, 4.2.6, 4.1.*)
> instances on AWS to terminate VPNs between each other and/or to other
> devices across the Internet.
> While investigating some application issues, I've noticed that on every VPNs
> I have random packet losses (from 1% to 4% over 100 to 300 requests sent).
> This only happens when the two following conditions are met: (a) AES
> encryption used, (b) IP packet size shorter than about (150+8+20)Bytes.

I've never seen this.

If xfrm statistics are compiled in, a counter is bumped for each packet
dropped by IPsec. You can check these counters in /proc/net/xfrm_stat.

This will tell you at least whether IPsec is the reason for your packet
loss.

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