There are several ways you can obtain your network license file. Some are easier than others.
1) Call Autodesk at 866-681-4359 and have your serial number and servers MAC and Hostname (computer name) available.
2) Use the old web interface at http://www.autodesk.com/register, which is a bit problematic right now.
3) (BEST-Recommended) The new web interface inside https://manage.autodesk.com
This new interface is much better than the old interface AND you do not have to rely on Autodesk hours, you can access it 24 hrs a day to generate your license.
Note: the only drawback I see to using the new web interface is that not all users will have access to it, it appears that only the subscription account manager and software coordinators can use this functionality.
1) Login to https://manage.autodesk.com
2) Scroll down on the Products list to one of your programs that is a network version and expand it.
3) Click the link to Generate Network License files.
4) Follow the on-screen instructions, most people will be selecting "Single Server" and one of the very cool things about this method is you can obtain ALL of your network licenses at one time and not have to use the tool multiple times (like the old web interface).
For the step by step process to generate the license go to the Autodesk kb article.
Please also see the Notes in the above kb article.
Contact us to learn more about Autodesk programs.
Technical Support: 888-528-4765 http://www.imaginit.com/support/overview