The ip-up file is responsible of adding routes to the routing table when a network connection is established. By modifying it, you can add your own routes. A great use case is when you want to access the TLM's Gitlab while on the VPN of a client.
First, you need to know wich interface to use for the new route.
ifconfig will show all interfaces available.
When VPNs Just Work™, they're a fantastic way of allowing access to a private network from remote locations. When they don't work it can be an experience in frustration. I've had situations where I can connect to a VPN from my Mac, but various networking situations cause routing conflicts. Here are a couple of cases and how I've been able to get around them.
In this example the VPN we are connecting to has a subnet that does not conflict with our local IP, but has additional routes that conflict in some way with our local network's routing. In my example the remote subnet is 10.0.x.0/24, my local subnet is 10.0.y.0/24, and the conflicting route is 10.0.0.0/8. Without the later route, I can't access all hosts on the VPN without manually adding the route after connecting to the VPN:
