Active Directory Sites and Services allows you to create a logical outline of your physical sites and links. Much the same as AD users and computers allows you to create a logical structure of you users and computers objects etc. Sites and Services also allows you to map and control active directory replication which is great for replicating to sites that maybe are not quite so well connected as others. This allows you to design active directory around physical boundaries and challenges such as a slow wan link to a branch office or even {shudder} a dial up link that is only connected irregularly.
By default when you create a new root forest a site is created within sites and services (helpfully named DEFAULTFIRSTSITE) and all domain controllers are added to the to the default first site. To take advantage of the features of sites and services you will need to create 3 different type of objects Those are subnets, Inter-site transport links, and sites. Sites are the objects for physical locations so for example if you had 3 sites, london, paris and isle of wight each location would be represented with a site. Inter-site transport links are objects that define how sites link to each other so if london and paris had a dedicated pipe between each other that would be a site link and if isle of wight had a dial up connection then that would also be a site link. Subnet objects define what subnet a site uses which allows client computers to interrogate DNS to find out which site they are on and therefore contact the local domain controller or other service that is sites and services aware.
To start configuring sites and services its always a good idea to change the name of the DEFAULTFIRSTSITE to something meaningful, so for example you can rename it to CorporateHQ. And also rename the DEFAULTIPSITELINK which at the moment has no use until you create an additional site. Now another cool thing whilst we are talking about links is that you can choose one of two different protocols when configuring the link which is either IP or SMTP. Yep I said SMTP the protocol mostly used for mail transport. I’ll explain more on that later.
Initially If you have more than one site link as we do in our example you will need to create the links first that will bind the sites toegether (remember that links are representations of physical links such as WAN connections or slower technologies such as dial up). To create a site link you will need to decide which protocol is best for the site link that you would like to create, you would use IP for an always up connection such as a site to site VPN, or better connection. Now because SMTP is good for queueing data and sending when the link is available you would use SMTP for links that are not always up such as dial up links or slow and unreliable connections to remote offices. I’ll explain more in later blog posts. Right click on the link protocol folder that you wish to use for the connection and select New Site Link, you will at the moment get a warning message about only having one site configured which obviously causes problems for site links as they have nothing to link to, at the moment you can safely ignore this message and click ok. Give you link a name and click ok.
Now to create your first additional site you need to right click on the sites container and click “new site” Choose a name for the site (something short but meaningful) and click next. Then select the sitelink that you would like to use to connect the site with. Then you will get a final message saying you need to take additional steps to correctly configure sites and services for replication.
Once you have created a site its time to start populating the site with configurable options. Now one thing that does underpin alot of what sites and services is about is the subnet configuration. By identifying which subnet a site uses, you enable clients local to that site to be able to find and use their local domain controller(s) or service is sites and services aware. Also when you create and promote other DC’s they will automatically add themselves to the correct site when they are created based upon their own IP address. To create a new subnet all you need to do is right click on the subnets container and select new subnet. Then enter the subnet details into the box and select the pre-created site that it should be associated with. So for example if our paris site uses 10.0.0.x as its address range you would enter 10.0.0.0/24 into the prefix box and then select the paris container.
I’ll blog about the configuration of your new sites and services topology which will allow you to define preferences and costs to the links to specify in what order they should be used etc.
