Identifying Network Topology and Performance Levels

At this point in the analysis phase, your focus really turns to the physical aspects of the network. Now you're looking at the physical topology, such as the connections between various locations and the connection speeds as well as the performance of servers on the network. Doing so enables you to set expectations so that you know before Active Directory is implemented how well the network and servers will perform within the new infrastructure and what possible upgrades should be suggested.

Identifying Constraints in the Existing Network Infrastructure

The existing network infrastructure is bound to have a significant effect on the Active Directory design. When analyzing the existing network infrastructure, you might discover constraints that must be considered. For example, you might discover constraints in the WAN connectivity between different locations where the connections are already heavily utilized or unreliable. Because there is a good chance that the physical network will not be upgraded, constraints such as these must be considered.

LAN/WAN Connectivity

Begin the assessment of LAN/WAN connectivity by determining the physical topology of the network. Document the network topology and the size of the network. After the layout of the network has been established, you can assess the connectivity between the physical networks. Documenting the connectivity within a business will assist you in designing an Active Directory structure that complements the physical layout. Not doing so could result in things such as regular replication occurring over a slow network connection.

A good starting point to get an overall picture of the existing network structure is to create a diagram that is representational of the physical network. The diagram should document such things as the LAN/WAN connectivity and bandwidth constraints. This provides a good reference point when planning Active Directory and the network infrastructure.

After you've documented the physical layout, you can determine the type and speed of connections within the different locations as well as the speed of the connections between them. Determining the appropriate speed of the links within an organization will depend on the amount of network traffic that is generated. Further analysis of the amount of network traffic generated throughout the business must be done to determine the amount of bandwidth that is available.

Completing these assessments will help the design team determine the best replication routes within the business and the optimum location for its servers.

Available Bandwidth

The amount of bandwidth available within an existing network environment will affect things such as the creation of Active Directory sites. A connection between two locations might be high speed and reliable, but if it is already heavily utilized, it might not have enough bandwidth available to support regular replication. This information could lead the design team to create sites on either side of the connection. Only a thorough analysis of the network traffic generated within an organization will give you a good picture of the available bandwidth. Using a network analyzer, such as Network Monitor, will help you determine the amount of traffic currently being generated.

The physical LAN and WAN infrastructure will influence not only site design but also the number of domains created and the placement of servers within a domain.

When determining the amount of traffic that is generated on the network and the available bandwidth, consider some of the following traffic-generating events and how often they occur:

• How often are users required to change their passwords?

• How many users log on to the network?

• When do the bulk of the logons occur?

• How many DNS queries are performed throughout the day?

• If DHCP is used, how often are users required to renew their IP addresses?

Interpreting Current Baseline Performance Requirements for Each Major Subsystem

In addition to security and availability, another aspect of the current setup that you must consider when designing Active Directory is performance. During your initial assessment of the existing network, you need to determine the current performance levels of the major subsystems (for example, memory and disk). After you've determined the current performance levels for servers on the network, you can set expectations for performance levels.

A good starting point for monitoring server performance is to use the performance tool that's included with Windows Server 2003. With the performance tool, you can monitor the real-time performance of the various subsystems. The information will help you determine what kind of performance can be expected. You can also use the information to identify any bottlenecks that currently exist on a server (and possibly address them before performing implementing Windows Server 2003 Active Directory).