Licensing and the Network Analyst extension
You can accomplish some tasks that are related to ArcGIS Network Analyst without the Network Analyst extension; however, you need to install and enable the extension before you can harness all of its functionality. This topic provides an overview of the functionality that is available depending on whether the Network Analyst extension is enabled.
ArcGIS Desktop with the Network Analyst license
All the network analysis and network dataset capabilities are available to you when the Network Analyst extension is enabled. Thus, you can perform any of the network analyses that Network Analyst provides; you can also create, edit, and build network datasets. This holds true whether you have ArcView, ArcEditor, or ArcInfo installed.
ArcView, ArcEditor, and ArcInfo
Keep in mind that although Network Analyst functionality doesn't encompass editing, you may need to edit features that participate, or will participate, in a network dataset. In such a case, your ArcGIS Desktop license level (ArcView, ArcEditor, ArcInfo) determines which editing tools are available and, thus, may affect the accuracy of the results. For example, ArcEditor offers functionality that ArcView does not, such as topologies, subtype editing, and advanced feature dataset management. ArcInfo builds on the capabilities offered by ArcEditor to include tools like Integrate, which creates vertices on intersecting lines. Higher ArcGIS Desktop license levels help you to more quickly and accurately model transportation networks.
ArcGIS Desktop without the Network Analyst license
The following capabilities are enabled even without a Network Analyst license:
- View properties of network datasets.
- View network dataset layers in ArcMap.
- View network analysis layers in ArcMap.
- Change properties of network analysis layers.
The only capabilities that you won't have access to are the following:
- Creating, building, and rebuilding network datasets
- Solving network analysis layers
Find Route
Even without an extension, ArcGIS Desktop provides route analysis capability through the Find Route dialog box. You can click the Find Route button 
on the ArcMap Tools toolbar to open the dialog box. Yet the Find Route dialog box doesn't give you the full range of analysis options that the Network Analyst route analysis layer provides.
ArcGIS Engine, ArcGIS Server, and the Network Analyst extension
Network Analyst functionality is also available as an extension to ArcGIS Engine and ArcGIS Server. A separate network license is required for each application. This means an ArcGIS Desktop license for the Network Analyst extension is not interchangeable with ArcGIS Engine or ArcGIS Server. You need a Network Analyst license specifically made for ArcGIS Engine to use Network Analyst functionality in ArcGIS Engine. To use similar functionality in ArcGIS Server, you need a license for the Network extension.