I have a site-to-site ipsec vpn with strongswan. It was working well
for 5-6 months then a day ago I have noticed something strange, that
from Site-A to Site-B (tunnel mode) only the upload bandwidth is capped
down to 20-30kbit/s inside the VPN.
I have tried various apps like ftp, scp on different ports it was the
same result. I also ran speedtest/wget on both endpoints just to make
sure that not the entire connection of those networks are capped.
Since outside parties cannot see anything from what's going on inside
the tunnel, first I was thinking that they started limiting the traffic
based on port (4500 udp) or based on protocol (ESP), that is easy to do.
In older versions of strongswan it's not possible to change the charon
nat port (probably wouldn't work anyway since most of the traffic should
be ESP (protocol 50)).
I have restarted the strongswan daemon on both endpoints multiple times
it did not change the situation (the bandwidth limiting was still present).
So my last idea was to make new vpn certificates. For my biggest
surprise with the new certificates the capping was gone and the
bandwidth went back to normal. I hope I don't have to put the old certs
back from backup just to make a point.
One of the ISPs must started tagging the ipsec traffic based on the
certificate and then do traffic shaping (QoS) on it to throttle down the
bandwidth. How is this even possible? I was thinking that an ipsec
connection is encrypted and random from the beginning. How can they
define a pattern to their whatever device to be able to mark this
Is there a part at the beginning of the connection sequence which is
always the same with using the same certificate?
Do I have to worry about here that my vpn keys got compromised?
Anybody ever experienced this?