After a 6-month struggle in trying to grep the internet looking for an answer in how to get Juniper’s SSL VPN client to work with Gentoo Linux, the fight is finally over.

There is a detailed post on the Gentoo forums about how to setup Juniper on Gentoo.

Some requirements are that you are using sun sdk 1.4, which you have to manually download from sun and install with portage.
The major show-stopper for me was not having the correct Kernel parameter set:

$ grep CONFIG_TUN /usr/src/linux/.config
CONFIG_TUN=y

Make sure you have TUN enabled in the kernel:
Device Drivers —>
Network device support —>
< *> Universal TUN/TAP device driver support

see the link above for my notes and step-by-step instructions.