Determining the Cost

Updated: April 26, 2012

Applies To: Windows Server 2008, Windows Server 2008 R2, Windows Server 2012

You assign cost values to site links to favor inexpensive connections over expensive connections. Certain applications and services, such as Domain Controller Locator (DCLocator) and Distributed File System Namespaces (DFSN), also use cost information to locate the nearest resources. Site link cost can be used to determine which domain controller is contacted by clients in one site if the domain controller for the specified domain does not exist at that site. The client contacts the domain controller by using the site link that has the lowest cost assigned to it.

We recommend that the cost value be defined on a site-wide basis. Cost is usually based not only on the total bandwidth of the link but also on the availability, latency, and monetary cost of the link.

To determine the costs to place on site links, document the connection speed for each site link. Refer to the "Geographic Locations and Communication Links" (DSSTOPO_1.doc) worksheet in Collecting Network Information for information about the connection speed that you identified.

The following table lists the speeds for different types of networks.

 

Network type Speed

Very slow

56 kilobits per second (Kbps)

Slow

64 Kbps

Integrated Services Digital Network (ISDN)

64 Kbps or 128 Kbps

Frame relay

Variable rate, commonly between 56 Kbps and 1.5 megabits per second (Mbps)

T1

1.5 Mbps

T3

45 Mbps

10BaseT

10 Mbps

Asynchronous transfer mode (ATM)

Variable rate, commonly between 155 Mbps and 622 Mbps

100BaseT

100 Mbps

Gigabit Ethernet

1 gigabit per second (Gbps)

Use the following table to calculate the cost of each site link based on wide area network speed (WAN) link speed. For WAN link speed that is not listed in the table, you can calculate a relative cost factor by dividing 1,024 by the log of the available bandwidth, as measured in Kbps.

 

Available bandwidth (Kbps) Cost

9.6

1,042

19.2

798

38.4

644

56

586

64

567

128

486

256

425

512

378

1,024

340

2,048

309

4,096

283

These costs do not reflect differences in reliability between network links. Set higher costs on any failure-prone network links so that you do not have to rely on those links for replication. By setting higher site link costs, you can control replication failover when a site link fails.

Community Additions

ADD
Show: