A number of reasons can lead to slow data transmissions through the VPN tunnel of the Advanced VPN Client.

This article describes the possible causes and solutions.



Low performance when using IPsec over HTTPS:

When using IPsec over HTTPS, the IPsec packets are additionally encapsulated in HTTPS, and the additional overhead results in a lower achievable performance.

IPsec over HTTPS is used automatically by the Advanced VPN Client if the VPN gateway cannot be reached by IPsec. This may be the case if IPsec is blocked by the provider, for example, or the VPN connection is established from a restrictive hot spot where only HTTP and HTTPS are allowed. In these cases, the lower performance has to be accepted in order for the VPN connection to be established at all.

If IPsec is not blocked, but IPsec-over-HTTPS is being used anyway, you should check the Advanced VPN Client profile in the submenu Advanced IPsec Options to see if UDP encapsulation is activated and the port is set to 444. In this case, enter the port 500 and switch to Standard IPsec. Please also see this article in our Knowledge Base.

Low performance without split tunneling:

With no split tuning configured, all of the data traffic is sent through the VPN tunnel. Data traffic destined for the Internet is transmitted via the Internet connection of the VPN gateway, which can slow down access to websites.

For more information and setup instructions, see this article in our Knowledge Base.

Check the load on the Internet connections:

Check the load on the two Internet connections, i.e. the one where the Advanced VPN Client is located and that of the VPN gateway. 

Example scenario:

Location A: PC with Advanced VPN Client, Internet connection with 100 Mbit download and 40 Mbit upload

Location B: VPN gateway, Internet connection with 100 Mbit download and 100 Mbit upload

  • If a computer at location A downloads a file from location B, but the Internet connection at location B is already under a load of 80 Mbit, then a download at location A has just a theoretical 20 Mbit at best.
  • An upload of a file from location A to location B is limited to a theoretical 40 Mbit, even if location B has more download bandwidth available.

Check the network interface:

Check which network interface the PC/notebook with the Advanced VPN Client is using to connect to the network. If you are using Wi-Fi, difficult environments may cause performance to suffer. If possible, connect the PC/notebook to the network using a LAN cable instead.

After changing the network interface to the LAN, open the profile used in the Advanced VPN Client, switch to the submenu Basic settings and set the Communication medium either to Automatic media detection or LAN (over IP).

We recommend that you use the automatic media detection for the communication medium if you frequently switch between different connection media (usually Wi-Fi and LAN). 

Low-performance data transmission and simultaneous use of VoIP telephony via the VPN tunnel of the Advanced VPN Client:

The function Prioritize Voice over IP (VoIP) in the Advanced VPN Client can result in the data transmission being severely restricted when simultaneously telephoning via VoIP and transferring data over the VPN tunnel.

When activated, the function Prioritize Voice over IP (VoIP) gives priority to VoIP packets. All other protocols are limited to a speed of 64 kbps.

The Prioritize Voice over IP (VoIP) feature is activated for the Advanced VPN Client when a VPN profile is created using the Provide remote access (RAS, VPN) setup wizard in LANconfig (both with and without 1-Click).

If you observe this behavior in your scenario, we recommend that you deactivate Prioritize Voice over IP (VoIP) as a test and check whether telephony still works satisfactorily.

The Prioritize Voice over IP (VoIP) feature is located in the profile used by the Advanced VPN Client in the submenu Line management.