ISP marking ipsec traffic based on certificate, how is this possible?

Hello list,

  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
  specific traffic?
  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?


Sure your VPN tunnel wasn't 'stuck' flowing through a less than optimal or saturated ISP upstream transit peer? Sometimes, just restarting your VPN may force the traffic through a different path in your ISP's network and clear up an issue. We manage many customer IPsec tunnels, hit similar situations where a restart works the best especially when the issue is not in under your control.

Nick Ellermann – CTO & VP Cloud Services

P: 703-297-4639
F: 703-996-4443

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If you’re using certificates, It could be possible you may have changed your VPN from IPSEC to SSLVPN.
In which case it now runs over TCP port 443.
So maybe they’re not doing traffic shaping on TCP 443.