Tech/Basics/Captive Portal Authentication
Introduction
When working from public places or just out and about some times the provided free wifi is troublesome. Often a system called a Captive portal is used. It was once known by the tool nocat-auth many years ago. The system uses a private network, isolated DNS and a web based portal to confirm your account or that you agree to not do bad things.
Problem
When using trusted DNS servers or when your network configuration conflicts with the private network you may not be able to reach the proper page to confirm your account or approval. You most often will get a name not resolved error regarding the DNS servers not having a path to resolve.
Solutions
Mobile Phone
You can connect with a secondary device and confirm the network settings by inspecting the network interfaces of the mobile device. It may be useful to just note the private network DNS servers and save them in a file.
Default Route
You can locate the default route of the private network and paste it into the browser and continue to load it.
root@lappy7:~# ip r default via 172.16.0.1 dev wlp4s0 proto static metric 600 1.1.1.1 via 172.16.0.1 dev wlp4s0 proto dhcp metric 600
Going to http://172.16.0.1 a few times and maybe clicking an I agree will get you online.