So I have been looking into designing an AD replication structure for a network which is designed around all sites connecting into a managed MPLS network. So really all sites just connect to the MPLS cloud and data comes out the other end the routing of the cloud was not under my control. All the sources I have found on the net talk about sites being linked to other sites via leased lines and to map your AD design to the network design. This doesn’t really work in an MPLS network as all sites are connected to each other. So in this situation I believe that link cost can be treated a little differently.
First I decided to have two types of links core links with a cost of 10 and default site links with a cost of 100. Now I decided to put all my core sites (HQ’s and sites with large user populations) in to one site link called the hub. It should be noted that the KCC will fully mesh all sites that are in one link so if you find you are going to have alot of core hub sites you may want to construct the mesh manually by creating individual site links for the core. I would say more that 5 core sites probably requires manual link creation.
Next you need to create site links for all of your other sites. It is recommended to only have 2 sites in a link (apart from the core) this means that you can have full control of your replication paths. If you require backup links you can add these using a link cost of say 200. I decided to have sites that connected to the same MPLS core networks link together. This means that your replication traffic will only traverse the network via the core hub sites and not all the other sites. This cuts down on unnecessary bandwidth usage.
You should have no more than default satellite sites connected to one hub site. If you do you ether need to make sure the hub site has the resources in bandwidth and server performance to take the load or create another hub site and move some sites across to the new site.
You will also need to decide on replication intervals and schedules. This can be decided by how often you make changes and how quickly you need them to replicate.
To monitor your replication system I would recomend installing Ultrasound from Microsoft it is free and will monitor and debug any issues you might get in the future.