Get the Network Analyst extension from the application.
[C#]
///<summary>Get the Network Analyst extension from the application.</summary>
/// 
///<param name="application">An IApplication interface.</param>
/// 
///<returns>An INetworkAnalystExtension interface.</returns>
///
///<remarks></remarks>
public ESRI.ArcGIS.NetworkAnalystUI.INetworkAnalystExtension GetNetworkAnalystExtension(ESRI.ArcGIS.Framework.IApplication application)
{
  ESRI.ArcGIS.esriSystem.IExtension extension = application.FindExtensionByName("Network Analyst");
  ESRI.ArcGIS.NetworkAnalystUI.INetworkAnalystExtension networkAnalystExtension = extension as ESRI.ArcGIS.NetworkAnalystUI.INetworkAnalystExtension; // Dynamic Cast
  return networkAnalystExtension;
}
[Visual Basic .NET]
'''<summary>Get the Network Analyst extension from the application.</summary>
''' 
'''<param name="application">An IApplication interface.</param>
''' 
'''<returns>An INetworkAnalystExtension interface.</returns>
'''
'''<remarks></remarks>
Public Function GetNetworkAnalystExtension(ByVal application As ESRI.ArcGIS.Framework.IApplication) As ESRI.ArcGIS.NetworkAnalystUI.INetworkAnalystExtension
  Dim extension As ESRI.ArcGIS.esriSystem.IExtension = application.FindExtensionByName("Network Analyst")
  Dim networkAnalystExtension As ESRI.ArcGIS.NetworkAnalystUI.INetworkAnalystExtension = TryCast(extension, ESRI.ArcGIS.NetworkAnalystUI.INetworkAnalystExtension) ' Dynamic Cast
  Return networkAnalystExtension
End Function