Cisco AnyConnect error “The VPN client agent IPsec engine encountered an error.”
Cisco
(AnyConnect)
Wednesday, 14 October 2020
by paul

Issue with the Cisco AnyConnect VPN network client. It displayed the error message “The VPN client agent IPsec engine encountered an error.” after authentication and failed to connect. The issue only occurred from specific ISP internet connects (Sky).
The error was due to the VPN split tunnel containing too many routes (1000+). Reducing the number of routes (<200) allowed the connection. Not sure why this only affected specific ISP internet connections.