I'm trying to install the Juniper Network Connect client on Ubuntu -- I'm wondering if any seasoned network admins or otherwise knowledgeable individuals know if it's possible for me to download the client directly from a 3rd party source, or if it is mandatory that I download it from the given network's vpn website. If the latter, can you explain why?
This is a bit of an odd question and I feel you have an underlying question which you haven't (directly) asked, so you might want to ask what you really want to know instead.
I don't know why you wouldn't want to download it from the gateway you're connecting to. I would trust the gateway I'm going through more than I would some "3rd party source".
In any case, once you have installed the Network Connect application, it can connect to different SSL VPN gateways (however I don't know if it has to be the same model of Juniper device on the other end).
The answer depends on what build & release of the SA software is installed on the Juniper devices. Newer builds typically have expanded support although this hasn't always been the case. Over time, Juniper released more features and support of Ubuntu in general. I can't remember which specific build was stable for Network Connect in Ubuntu, but I do remember seeing Juniper documentation specifically naming certain versions of Ubuntu in their "supported" OS section. Like I mentioned earlier, later builds seemed to expand support for Ubunto and Linux in general. If its 6.x or 7.x, things will probably be ok. This link lists the supported OS/apps in V7.1r4.0.
More to the point of answering your question, Juniper wants you to get it directly from whatever system(s) you're connecting to. That way there is no confusing the correct version needed. It is not available 3rd party or from non-admin download from Juniper. Their licensing is all back-end and based on concurrent sessions. In fact, network connect was licensed separately on top of this, but I digress. Having the software is legal but you can't use it with anything else. They provide the clients in their appliance build releases and only the necessary version is included with the build. Therefore, it automatically downloads when trying to login. System admins have the ability to extract the software from the appliance and publish it. This is what I used to do. I put it up on our company's external login page, in the case that the auto-installer was blocked by the user's computer. Users could manually down and install it if they wanted to. We did have a few people who needed to login to other juniper instances not controlled by me, and their different versions of the network connect software coexisted just fine.
As a side note, this Juniper Network Connect-Ubuntu guide is one of the best I've seen.
Does this answer your question?