[strongSwan] IPsec tunnel problems under high load

Martin Willi martin at strongswan.org
Wed Jul 2 15:15:14 CEST 2014

Hi Noel,

> When my desktop is under high network load (everything over 50 Mbit),
> I can't initiate new TCP connections over the VPN, nor send UDP or ICMP
> packets.

For the local traffic you generate, do you see corresponding ESP packets
leaving your host? Do you see associated ESP packets carrying reply

> The errors shown in nstat (or netstat -s) increment dramatically when
> that happens.

Do you see any errors in /proc/net/xfrm_stat?

What is your kernel version?

> I already tried incrementing the replay window to over 32, but
> strongSwan just sets it to 0, if I try that.

To configure larger replay windows, charon uses the newer ESN replay
windows configuration Netlink attribute. AFAIK that is not supported in
the "ip" tool, hence it falsely reports 0 as replay window for such SAs.


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