Site links

slinuxuzer

James conrad mentions in cbtnuggets that you can make differnet connections for say a T1 and a Isdn link that give you a route to a different site. How can you do this all I see is the automatically generated connections, (this might be beacuase I am using a vmware lab and have only one route between my machines.

royal

So let's say you have a hub and spoke model. 1 datacenter and 50 branch offices. Every branch office has a dedicated T1 connection directly to your datacenter hub. This datacenter is in Chicago which we will denote as CHI. Your branch offices are scattered around the USA. Because you're using a hub and spoke model, you'll do the following types of site links.

Branch1-CHI
Branch2-CHI
Branch3-CHI
...
...
...
Branch50-CHI

By default, Site Links are transitive by nature. So if CHI went down and Branch 1 would have direct connectivity with another branch, it would essentially start trying to replicate to another branch. This all depends on how the Knowledge Consistency Checker (KCC) determines connection objects. The way this happens is the KCC runs every 15 minutes and checks the Intersite Topology Generator (ISTG) and chooses a DC to be your inter-site replication bridgehead server based on GUID of server if you do not have one/two statically assigned. Make sure if you statically assign one, that you use IP if possible instead of SMTP and you choose at least 2 since the KCC won't dynamically choose 1 if 1 fails.

So when the KCC runs, it'll check all the Site Links and create Connection Objects appropriately as it sees fit. You can create custom connection objects, but I don't recommend it. In your situation, if you ONLY want the datacenter to be the end all of replication and your branch offices don't have connectivity with each other, you can turn off site link transitivity.

In the case where you have 2 datacenters, 1 in NA and 1 in EU, you can create the following site links:
USA-EU
USABranch1-USA
USABranch2-USA
...
...
...
USABranch25-USA
EUBranch1-EU
EUBranch2-EU
...
...
...
EUBranch25-EU

Again, the KCC will eventually run and determine what servers replicate with what other servers. If all branch offices and datacenters have connectivity together, you can leave site transitivity on so if one server goes down, you can still replicate in a transitive fashion. Once the downed server comes back up, the KCC will see that and re-adjust the connection objects as it sees fit.

As for costs, I'd try to associate costs on your link depending on the speed. It'll help when transitivity goes into afffect. So if all your branch offices connect to your datacenter but all branch offices can talk to each other, I'd leave site transitivity on. If all your branch offices connect via a 10mbit link but 1 branch office is only connected via a T1, make sure that site link with the T1 connection has a higher cost so if site transitivity ever goes into affect, the KCC can make appropriate decisions based on that cost.

Hope that helps.

slinuxuzer

Royal, once again your great. I am a big fan of yours. lets say I have two sites and there are two links say a t1 and a slower link like a isdn connection, how can I tell what line will be used when I create my link?

dynamik

Site Link Cost

If you have two site links, it will use the one with the lower cost. Site links are cumulative too. For example, lets say you have three sites. There is a T1 between sites 1 and 2 as well as sites 2 and 3. There is also a 128k ISDN between sites 1 and 3. If you assign the T1 links a cost of 50 and you assign the ISDN a cost of 150, site 1 will use the two T1 links to get to site 3 instead of the direct ISDN link because 100 is a lower cost than 150 (this of course assumes your network can route traffic that way).

The value you assign is completely arbitrary. The above example would have worked with the T1s having a value of 1 and the ISDN having a value of 3. In practice, you'd probably want to come up with some sort of standard way to determine the value of site links. Maybe assign a value of 50 for every 512k a connection has. This way, you're not just arbitrarily assigning random numbers to your site links and it will give you some flexibility if things change later on.

royal

Yep, that goes back to my whole point of all your sites having 10mbit lines and 1 site having a T1. You'd assign the Site Link that contains the T1 link with a higher cost.