In larger Active Directory environments there is typically more than one domain controller. Some of them are used for redundancy, others to build different administrative domains. But in environments with multiple physical locations each location often has at least one local domain controller to reduce latency and network load between the locations. Now clients have to find the local or nearest domain controller. For this the concept of sites was introduce where each physical location can be seen as an individual site with a unique name. The naming scheme for DNS service records was extended so that clients can first try to find the needed service in the local site and can fall back to look in the whole domain if there is no local service available. Additionally clients have to find out about which site they belong to. This must be done dynamically because clients might move from one location to a different one on regular basis (roaming users). For this a special LDAP request, the (C)LDAP ping, was introduced.