Bandwidth

Bandwidth is the most important practical consideration affecting intrasite replication on your network. Although sites are conveniently defined by subnets, it is important to understand that the reason for this choice is that subnets are typically well-connected. This means that subnets are generally, but not always, an effective way to determine sites.

To organize your sites effectively, consider replication requirements and available connectivity. Find a balance that ensures domain controllers in the same site are sufficiently well-connected to handle the frequent exchange of directory information, while not exacting what you consider to be excessive costs (such as high financial expense or compromised network performance).

When considering bandwidth, you may want to combine several subnets into one site, or split one subnet among several sites, such as in the following instances:

• One large subnet split into three subnets.
  You have very poorly connected computers, including several domain controllers in one subnet. Create several smaller subnets that are better connected than they were as one large subnet. For this to be effective, each new subnet should contain a domain controller.
• Several small subnets combined into fewer, larger subnets.
  You have several subnets that are all well-connected or you have fewer domain controllers than subnets, but you want several subnets to be in a single site. To do this, add multiple subnets to one site.

For more information about how bandwidth may affect the way you configure sites, see Replication between sites.