libc6-i386 vs libc6:i386 (for vpn client)

[Ross Boylan <rossboylan@stanfordalumni.org>]

Judging from https://wiki.debian.org/Multiarch/HOWTO, which doesn't
seem current but is all I could find, if I'm on the amd64 architecture
and want to support i386 I should expect to get packages like
libc6:i386.  There are a number of other packages that seem to have
versions for 32 bit without needing to specify an architecture suffix,
e.g. lib32z1 (32 bit version of zlib1g I think).

Further, I have those packages though I don't think I installed them explicitly.

Finally, I have not issued the command
dpkg --add-architecture i386
though the wiki made it sound as if I would need to to get 32 bit libs.

Could anyone explain what is going on and what I need to do so I can
run a 32 bit app?  I'm trying to install Juniper Networks proprietary
client, which includes a 32 bit library binary without the source.

Thanks.
Ross Boylan