• Static Network Diagram Software (1^st Generation)
  Such as Microsoft Visio.  Like any general-purpose diagramming software, it is a piece of electronic paper that network engineers write any network symbols on. Low cost, but no network intelligence.
• Static Network Diagram Software with Auto-Discovery (2^nd Generation)
  Such as Opnet NetMapper and Solarwinds LAN Surveyor.  This type of tool has network discovery capability.  Trained engineers can build static Visio diagrams of predefined areas quickly, leveraging the discovery results. 
• Dynamic Network Diagram Software (3^rd Generation)
  Invented by NetBrain.  Dynamic diagramming software automatically builds network diagrams from underlying data-model.  Besides automating network diagram, dynamic network diagram software is also a visual troubleshooting and network design platform.  Each network symbol in the diagram is actually a Smart Object, which enables the dynamic network diagram to update itself when live network changes are made.  It is capable of diagnosing performance issues within the network changes.
  Check out full capabilities of dynamic network diagram.

• Is your network well documented now and infrequently changed?

  If your network is well documented and rarely changes, a static network diagram tool such as Visio may serve your needs well.  However, if your network lacks accurate documentation to start with and frequently changes, considering a 3^rd generation dynamic diagramming tool will allow you to stay up-to-date by creating network diagrams automatically by using data collected from live network.  If network diagramming tasks are only a small portion of the network such as certain LANs, a 2nd-generation tool is also fine.

• What is the size of your network?

  The complexity of network diagramming goes up exponentially with the number of network devices.  The size and activity of your network are important factors in deciding the level of diagramming your company will need.

  If your network has fewer than 15 network devices (routers, switches or firewalls), a simple 1^st generation software such as Visio might be enough to manage the network.

  For medium size network with up to 100 network devices, the 2^nd generation tools or entry-level 3^rd generation tools may be a good investment to deal with the increased complexity of the network.

  For large networkwith tens of thousands of network devices, investing an enterprise-grade 3^rd generation tools should be considered.  If the diagramming tool’s sole purpose is to create a set of static network diagrams and there is no need to keep them updated (e.g. for one-time network assessment), then a 2^nd generation tool could be used.

• Is your business subject to security compliance requirements?

  Does your industry have to comply with security standards such as PCI, SOX and HIPPA?   If your organization is required to document every network change - having network diagrams alone will not be enough.  In these cases, 3^rd generation diagramming tools with advanced documentation features can save you countless hours by instantly creating the proper documents needed for security compliance.

• What's required by your job?

  The level of work required is also a strong indicator of the type of diagramming software needed.  For a casual user of network diagrams, the 1st-generation tool might be enough.  For a full-time network drafter, investing in a 2nd-generation or 3rd-generation tool is necessary.  For troubleshooters or network consultants looking for diagram automation for complex network, NetBrain’s 3rd-generation diagramming tool can be extremely useful.  The 3rd-generation diagram tool enables you to work on unfamiliar networks instantly because it not only creates diagrams on-the-fly but it also features a full network design and troubleshooting environment.

A network diagram is required by virtually every network task.  As a result, diagramming automation is an investment in productivity gain across the board.  3^rd generation tools integrate network troubleshooting, network design and network assessment with network diagramming process - making the return on investment as short as 6 months.

In the real world, every engineer spends a significant amount of time in diagram-related tasks - building new diagram, updating an old diagram or working off an existing diagram.  Assuming diagram automation saves 0.5 hour each day for those tasks, it adds up to $6,250 saving each year.

* Based on annual salary of $70k