Thank you @Lisias for your investigation.
So the easy guide to access KSP forum bypassing the current DNS issues on Windows is:
Press start and search for the Notepad
Right click on it and execute it as administrator
File -> Open
Paste this path on the File Explorer's address bar: C:\Windows\System32\drivers\etc
If you see an empty folder, use the filetype selector on the bottom right and chose "All Files (*.*)"
Select the "hosts" file and click Open
Paste this line at the bottom of the file (use enter to add a line if necessary): 172.64.145.232 forum.kerbalspaceprogram.com
Save the file
Close and reopen the whole browser
Now you can access the forum
I hope this post can help non-tech people who will see this through secondary boards, for example i've seen screenshots of @Lisias's post on reddit
Remember to remove the added line from your hosts file once the technical problems are fixed
Good luck to the system admins who are working on the problem