While data is usually replicated from a single master server to subordinate servers, Active Directory offers multimaster replication. The single-master replication has following drawbacks: it has a single point of failure, there's geographic distance from master to clients performing the updates, and less efficient replication due to single originating location of updates. With multimaster replication, you can avoid these but you have to first create a site topology and define how the domain controllers replicate with each other. The Knowledge Consistency Checker tool sets up and manages the replication connections. Subnets are added to site with 32 bit or 128bit IP addressing to determine relative locations on a network. AD sites are defined in terms of a collection of well-connected AD subnets. Replication flows are setup between sites and DFS shares or DCs are located using sites. Sites are used to perform DNS queries via the DC locator service which finds the nearest DC or the global catalog. Most members of a domain dynamically determine their site when they start up. By default, there's one site created automatically. Multiple sites can be defined for a single location to segregate resources.
Site links allow you to define what sites are connected to each other and the cost associated. Site links are used for replication and can support IP or SMTP. The default replication happens via IP but in some cases where the connectivity is poor or unreliable. These site links help a DC to determine which other sites to cover in addition to its own site for someone to logon to that site. As a trivia, if the network is not fully routed i.e. not all site links are available, then bridges have to be defined between sites. Connection objects specify which DC replicate with other DCs and are generally managed by the DC themselves. It isn't always possible to allow AD to manage all of these connections.
Knowledge Consistency Checker tool automatically maintains and generates the connection objects and knows how to replicate them and when. It uses two algorithms one called intrasite and another called intersite. The intrasite is designed to create a minimal latency ring topology that guarantees no more than three hops between any two DCs in the site. The intersite on the other hand, tries to keep the sites connected via a spanning tree algorithm so that replication can occur and uses the site link metrics to make the connections. RepAdmin is a commandline tool for administering replication. Replmon is a graphical utility for managing and monitoring replication.
Replication is done with either update sequence number (USN) or timestamps. Each DC maintains its highest combined USN for all naming contexts.
Site links allow you to define what sites are connected to each other and the cost associated. Site links are used for replication and can support IP or SMTP. The default replication happens via IP but in some cases where the connectivity is poor or unreliable. These site links help a DC to determine which other sites to cover in addition to its own site for someone to logon to that site. As a trivia, if the network is not fully routed i.e. not all site links are available, then bridges have to be defined between sites. Connection objects specify which DC replicate with other DCs and are generally managed by the DC themselves. It isn't always possible to allow AD to manage all of these connections.
Knowledge Consistency Checker tool automatically maintains and generates the connection objects and knows how to replicate them and when. It uses two algorithms one called intrasite and another called intersite. The intrasite is designed to create a minimal latency ring topology that guarantees no more than three hops between any two DCs in the site. The intersite on the other hand, tries to keep the sites connected via a spanning tree algorithm so that replication can occur and uses the site link metrics to make the connections. RepAdmin is a commandline tool for administering replication. Replmon is a graphical utility for managing and monitoring replication.
Replication is done with either update sequence number (USN) or timestamps. Each DC maintains its highest combined USN for all naming contexts.
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