Site link cost

The cost value of a site link is an arbitrary number that helps the replication system in AD determine when to use one link over others. Cost values determine the paths that replication will take through the network. To obtain cost factors, the following formula is typically used:

Cost = 1024 / Log (available bandwidth in Kb)

Following are some examples:

Available Bandwidth Cost'

9.6 1042

19.2 798

38.8 644

56 586

64 567

128 486

256 425

512 378

1024 340

2048 309

4096 283

8192 261

16384 242

32768 227

65536 212

131072 200

1 You can use a simple descending or ascending cost table (such as 100, 200, 300). However, scientifically calculated costs derived from a cost formula lessen the chance of assigning incorrect cost factors to various links.

Table 10-4 is a site link chart that can be used in the site/replication topology architected here. As you can see, Ring 1 links have the lowest cost values.

Table 10-4: Link Schedule/Notification Data

Ring

Schedule

Notification

Intersite

Ring 1

Every 15 minutes

Yes

Ring 2

60 minutes

No

Ring 3

Once a day at midnight

No

Intrasite

N/A

Automatic

Every five minutes

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