Additional Domain Controlers (ADC)
In order to add fault tollerance & load balancing in nw, we will add another domain controler, called ADC. If our main DC fails, then ADC will take place.
IN NT based env PDC will update every thing. In win2003 ADC are responsible by repliaction. Knowledge Consistency Checker (KCC) will update evry 15min.KCC will ensure that all db are sync through the process of replication Topology Generator(TG) will check every 15min, which domain controler is online and it will built topology on the basis of online machienes .



replication are of two types:

IntraSite(with in the site): Within same physical location.Replication occurs every 3Seconds. Topolgy is generated by a component called ISTG(Intrasite Topology Generator). ISTG select one bridge Head (BH). Each dc will replicated with atleast 2 others dc. so dc will only replicate with it's partners

InterSite:Multiple physical location. it happens every 180min. if the size of data is above 50KB then data will be compressed.Topolgy is generated by a component called TG. replication are controled Only by BH. And BH exchanges update from one site to another site. Different sites are created to control and localize sites.

dcpromo->select additional server->type your main DC name(shahid.local)

MsMgtCon->mmc->file->add remove snapin->ad users & comp & any other you need->File->Save
replmon->to open replication monitor(we need to install it from cd)