Inter-site Replication - Page 3
As the name implies, the Cost setting lets you associate a specific cost with the site link. However, this isn't usually a cost in terms of dollars, but bandwidth. The Cost setting comes into play when you have redundant physical network links between sites. For example, suppose your normal connection was through a T-3 line. Now, suppose you had an SMTP-based site link bound to a dial-up ISDN connection. Needless to say, you'd probably want all your traffic to flow through the T-3 line because of its high speed. Therefore, you'd set a very low cost to the T-3 line and a higher cost to the ISDN line. Because Windows 2000 always uses the link with the lowest cost, the T-3 line would always be used unless it was unavailable, in which case Windows 2000 would use the link with the next lowest cost--in this case, the ISDN connection.
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Another attribute you can alter through the site link's properties sheet is the replication schedule. As you can see in Figure 3, the properties sheet contains a setting that allows you to control how many minutes pass between each replication cycle. The amount of time you set is entirely up to you. Typically, you should base the amount of time used for the replication cycle on two factors: the impact replication traffic has on your physical network link between the sites, and how often users in each site need Active Directory updates from the other site.
If you like, you can even get a little more creative with the replication schedule by clicking the Change Schedule button. When you do, you'll see the window shown in Figure 4. As you can see, this window allows you to enable or disable replication based on the day of the week and the time of day. For example, if 9:00 AM on weekdays tends to be the time when your WAN links have the highest traffic volume, you might disable replication during that period.
Figure 4: You can enable or disable replication based on the day of the week and the time of day.
Conclusion
As you can see, Active Directory replication is almost a science in itself. So far, I've covered only the first two items on my five- step list for configuring Active Directory replication. I'll begin discussing the concept of creating Site Link Bridges in Part 3 of this article series ( Building Site Link Bridges ). //
Brien M. Posey is an MCSE who works as a freelance writer. His past experience includes working as the director of information systems for a national chain of health care facilities and as a network engineer for the Department of Defense. Because of the extremely high volume of e-mail that Brien receives, it's impossible for him to respond to every message, although he does read them all.
