Network Administration: License Server

Some programs let you purchase network licenses that enable you to install the software on as many computers as you want, but regulate the number of people who can use the software at any given time. To control how many people use the software, a special license server is set up.

Whenever a user starts the program, the program checks with the license server to see whether a license is available. If so, the program is allowed to start, and the number of available licenses on the license server is reduced by one. Later, when the user quits the program, the license is returned to the server.

One of the most commonly used license server software is FlexLM, by Macrovision. It is used by AutoCAD as well as by many other network software applications.

FlexLM uses special license files that are issued by a software vendor to indicate how many licenses of a given product you have purchased. Although the license file is a simple text file, its contents are cryptic and generated by a program that only the software vendor has access to. Here’s an example of a typical license file for AutoCAD:

SERVER server1 000ecd0fe359
VENDOR adskflex port=2080
INCREMENT 57000ARDES_2010_0F adskflex 1.000 permanent 6
VENDOR_STRING=commercial:permanent BORROW=4320 SUPERSEDE
DUP_GROUP=UH ISSUED=07-May-2007 SN=339-71570316 SIGN="102D
85EC 1DFE D083 B85A 46BB AFB1 33AE 00BD 975C 8F5C 5ABC 4C2F
F88C 9120 0FB1 E122 BA97 BCAE CC90 899F 99BB 23C9 CAB5 613F
E7BB CA28 7DBF 8F51 3B21" SIGN2="033A 6451 5EEB 3CA4 98B8 F92C
184A D2BC BA97 BCAE CC90 899F 2EF6 0B45 A707 B897 11E3 096E 0288
787C 997B 0E2E F88C 9120 0FB1 782C 00BD 975C 8F5C 74B9 8BC1"

(Don’t get any crazy ideas here, this license file so that it won’t actually work!)

One drawback to software that uses a license server is that you have to take special steps to run the software when the server isn’t available. For example, what if you have AutoCAD installed on a notebook computer and you want to use it while you’re away from the office? In that case, you have two options:

  • Use virtual private network (VPN) software to connect to the network. After you’re connected with the VPN, the license server will be available so you can use the software.

  • Borrow a license. When you borrow a license, you can use the software for a limited period of time while you’re disconnected from the network. Of course, the borrowed license is subtracted from the number of available licenses on the server.

In most cases, the license server is a mission-critical application — as important as any other function on your network. If the license server goes down, all users who depend on it will be unable to work. Don’t worry; they’ll let you know. They’ll be lining up outside your door demanding to know when you can get the license server up and running so they can get back to work.

Because the license server provides such an important function, treat it with special care. Make sure that the license server software runs on a stable, well-maintained server computer. Don’t load up the license server computer with a bunch of other server functions.

And make sure that it’s backed up. If possible, install the license server software on a second server computer as a backup. That way, if the main license server computer goes down and you can’t get it back up and running, you can quickly switch over to the backup license server.