I sure wish there was an easy way to do this! I can't tell you how many times I'm NOT told about new locations and thus new network IP ranges that are set up somewhere, and all machines in that location start failing to download pkgs because they are seen as being "outside" the network and thus get bumped to our external DMZ sharepoint. But because they are in fact inside, they can't hit the share and the pkg download fails. It happens like every month at least. I would LOVE a way to track down internal IP ranges I'm not being told about so I can set them up in the Network Segments section, but I don't know of an effective way to do that.
The best advice I can give you is to make friends with someone on your network administration team and ask them if they would be so kind as to output a spreadsheet of all known IP ranges (start and end IPs) and what they correspond with for you to use.
