There are, as usual,
several VPN toolkits available for Linux. Surf the Internet for
ipsec-tools ("racoon") and
open/SWAN.
Having had a
decidedly "love-hate-
hate" relationship with
both of these beasts ...
... I shall wish upon you the good-fortune that perhaps, "whatever distro you are presently using" will have embraced one-or-the-other of these tools and will have made it particularly easy for you to use them, so that you might perchance easily accomplish your
objective of "actually connecting with a chosen appliance" instead of the
curse 
of "wrestling with a blankety-blank-excuse-for-a tool."
Look at
all of your options. If you can go to OfficeMax and buy a VPN-capable hardware router for $~60 that knows how to communicate successfully with a "Juniper ns5gt appliance," (blah, blah, blah...) then
by all means do so.
