Behind the Scenes with Active Directory - Page 2

By Brien M. Posey | Posted Nov 2, 2000
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Two types of replication are at work within Windows 2000: Replication occurs within sites and between sites. As you might have guessed, replication within a site takes priority over replication between sites. This is the case for a couple of reasons. First, there's usually more demand for the information being replicated within the information's own site. For example, suppose your company has two sites: USA and China. If you're a member of the USA site, you probably communicate frequently with other members of the USA site and thus need very up-to-date directory information within that site. However, the average worker will seldom have to communicate with the China site; so, although directory updates between the two sites are important, they aren't as important as directory updates within the sites.

CrossLinks

The other reason for the less frequent updates between sites is that many times, sites are linked by a low-bandwidth connection. For example, in our USA/China site example, the sites might be linked by a T1 connection, but they would definitely not have the 100Mbps connection present within the sites. Therefore, to keep from hogging the precious bandwidth, replication between sites isn't constant.

Another fascinating aspect of directory replication is the way it's performed within a site. As you build your site, Windows 2000 automatically arranges the servers within the site into a ring structure. That way, any one server can fail and replication will still function, because ring structures always provide two paths for data to flow from each server. For example, suppose you have servers named A, B, C, and D, and that the normal replication path is A to B to C to D to A. Now, suppose that server B fails. In a linear structure, replication will fail, because A can't communicate with B. However, in Windows 2000, replication will revert to using the path of A to D to C and C to D to A. You can see an illustration in Figure 1. //

Figure 1: Replication within a site works in a ring structure.

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.

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