In this chapter, I discuss administration of sites, subnets, site links, and related components. Active Directory sites are used to control directory replication traffic and isolate logon authentication traffic between physical network locations. Every site has one or more subnets associated with it. Ideally, each subnet that is part of a site should be connected by reliable, high-speed links. Any physical location connected over slow or unreliable links should be part of a separate site, and these individual sites are linked to other sites using site links.