My office requires F5 VPN (to which F5 provides an interface with the Debian package f5pvn) to connect to on-campus resources from off-site. It works, but if I understand correctly, having the program running means that all my traffic travels through the VPN. I only want to use the VPN when e.g. I'm making an SSH connection to an on-campus server. How can I accomplish this?
I've seen many related questions, such as this one on Super User, but descriptions on how to do this on Linux seem to assume you're using OpenVPN.
You are correct that this is a matter of setting up the proper routes so that only traffic directed to your campus resources goes through the VPN. Probably the simplest way is to le NetworkManager deal with it. You can install the f5vpn plugin for NetworkManager (https://github.com/ohwgiles/NetworkManager-f5vpn) and then use the GUI to create your connection. Under the IPv4 tab of the GUI, you just need to select "Use this connection only for resources on this network" to limit the traffic to the subnetwork associated with the VPN.
Disclaimer: as I don't have an f5vpn account, I cannot test this, but works with other VPNs I use.