Do you know a way to test various Active Directory (AD) designs over our WAN links without affecting our production network?

A. Although plugging a few Win2K servers and workstations into a lab to evaluate new features and application compatibility is simple, determining exactly how your new Win2K environment will behave on your existing WAN is tricky. You might have heard that AD sites permit more efficient and intelligent replication than NT 4.0 permits. However, in a Win2K network, you can perform other types of replication, such as replication of the three AD contexts, Global Catalog (GC) replication, File Replication Service (FRS) replication, and replication types that other Win2K services use.

You want to know how the new network will "feel" to an end user or administrator working from a particular site. Therefore, you need a WAN-link emulation tool that lets you model your proposed network design by strictly controlling the amount of bandwidth permitted to pass through various ports on a router (e.g., Ethernet ports on a multiport NIC or multiple NICs).

Because many organizations face the challenge you face, several companies have developed WAN-emulation solutions. Some of these solutions are hardware-based, some are software-based, and others are hardware-software hybrids. These solutions typically utilize Quality of Service (QoS) control mechanisms because bandwidth management is what QoS is all about. (Win2K's network device interface specification—NDIS—5.0-enabled network drivers support these mechanisms.)

Typically, these products let you emulate any type of WAN link—from a modem to a T3 connection—with speeds ranging from 2400bps to more than 100Mbps. You'll definitely want to shop around for your WAN-emulation solution because prices vary widely. An example of such a solution is Lightspeed Systems' QoS Control. As Win2K deployments accelerate, I predict that these products will become a necessity.

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