Under the built-in client, this is solved by:
setting the following on the VPN custom connection:
a) "lifetime time 24 hours;" or more
b) dpd_delay 0;
c) proposal_check claim;
This can be done by creating a file, e.g. /etc/racoon/fix.1.1.conf and adding the lines above in there. Also ensure that the line "include /etc/racoon/*.conf" is not commented out in /etc/racoon/racoon.conf.
