In my previous article in this series, Planning a Sites and Services Architecture for Exchange 2007, I explained that Exchange 2007 does not have its own built in routing topology, but rather piggybacks off of the Active Directory site structure. In this article, I want to give you a little bit of practical know how to go along with the more theoretical material that I covered last time.
What Are Site Links?
The first thing that you need to know about Active Directory sites is that the sites themselves are a logical structure that mimics your network’s physical topology. Typically, each site will represent a well connected area of your network. Some administrators like to create a separate site for each network segment, but I tend to prefer to create sites based on connectivity speed. My rule of thumb is that there should be a site link for every WAN connector, and every part of your network that is separated from another part by a WAN link should be represented by a site.
Creating Site Links
Creating the sites themselves is simple. To do so, open the Active Directory Sites and Services container. When you do, you will see that Windows has automatically created the first site for you, as shown in Figure A (it’s called Default-First-Site-Name).
The first site is created automatically.
If you are going to be creating multiple sites, then the first thing that I would recommend doing is renaming the built in site so that it better reflects its purpose on the network. You can rename the site by right clicking on it, and choosing the Rename command from the resulting shortcut menu.
Once you have renamed the default site, it’s time to begin creating the other sites that will be used by your network. To do so, just right click on the Sites container, and choose the New Site command from the resulting shortcut menu. When you do, you will see the dialog box that’s shown in Figure B.
You must select a site link object.
As you can see in the figure, this dialog box asks you to enter the name for your new site, but it also asks you to choose a site link object. The reason for this is that at the present time, the Active Directory has no way of knowing how your network is physically laid out. You need to tell the Active Directory which sites are physically connected to which other sites, and you do this by selecting a site link connector.
At the present time, there is only one site link connector to choose from, but you can create additional site link connectors by navigating through the console tree to Sites -> Inter-Site-Transports -> IP, and right clicking on the IP container, and choosing the New Site Link command from the resulting shortcut menu. When you do, you will see the dialog box that’s shown in Figure C.
A site link must contain at least two sites.
As you can see, you must assign a name to the site link that you are creating. Generally, you will want to assign the site link a descriptive name that reflects its purpose. The New Object – Site Link dialog box will also list all of the sites in your organization and ask you to select which sites will be connected by the link. By creating site links you can begin to reconstruct your network’s physical topology using the Active Directory site structure.
In fact, you can even (and should) map the sites that you have created to subnets on your physical network. To do so, just right click on the Subnets container and choose the New Subnet command from the resulting shortcut menu. When you do, you will be prompted to enter the subnet range and to choose the site that the subnet corresponds to, as shown in Figure D.
You can map subnets to specific sites.
I mentioned earlier that a site may include multiple network segments as long as those segments are connected by high speed links. If your network uses such a design, then you will have to enter each of a site’s subnets individually.
In this article, I have shown you how to create sites and site links. In the next article in the series I will talk about moving servers into the sites, and about site replication.