Martijn
First of all it would be a great idea to actually be sure that the issues are generated by the VPN. It happened to me a lot of times where a customer blames the VPN or the appliance, but after performing a tcpdump / fw monitor analysis we could verify that the latency was from the server site.
Is the RSA Authentication server on the same network as the VPN Firewall?
If you go through SSL VPN you still have latency issues?
Basically what you want to check by performing a TCPDUMP / FW MONITOR is to check where is the delay:
Check the incoming request and the respective time (i, I, o O) and then check if the reply from the server is delayed or not. You may need to turn of SecureXL to perform this test correctly.
If you have ruled out that it is a VPN issue then it would be a good idea to check if the issue persist when using the SSL VPN, you will need the Mobile Access for this to work.
Finally I have faced some issues of VPN with s2s tunnels and remote access latency due to clamping, you can check sk90200 and sk98074, generally with the kernel parameter is enough.
Hope it helps,
Federico Meiners
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https://www.linkedin.com/in/federicomeiners/