Routing links

Applies To: Windows Server 2003, Windows Server 2003 R2, Windows Server 2003 with SP1, Windows Server 2003 with SP2

Routing links

If your organization has more than one Windows Server 2003 family site, you must create routing links to guarantee that messages can be routed between different Windows Server 2003 family sites. The route taken by messages between sites can be determined by the routing-link costs. All routing links are assigned a default cost of 1. Change routing-link costs only in the case where alternative routes are possible over the existing routing links and you want to enforce one route over another route using the costs of the individual links. For more information on configuring routing links, see Configuring routing links.

Link costs can be used to select the best intersite message route and may be based on the speed or the monetary cost of the underlying physical communication link. After you determine the number of Windows Server 2003 family sites in your forest, decide if you need to specify different costs for routing links. For information on how to change routing-link costs, see Change the cost for a routing link.

For information on sites, see Deploying in a domain environment.

Routing link example

A routing link that connects sites A and B has four site gates (SG1-SG4). If SG1 and SG2 belong to site A, SG3 belongs to both sites A and B, and SG4 belongs to site B, messages can be routed through one of the site gates of site A (SG1, SG2 or SG3) and then through one of the site gates of site B (SG3 or SG4). However, if the messages are routed through SG3, which belongs to both sites, they will reach the destination computer in one less hop. Thus, messages are routed preferentially through SG3. In the general case, if a routing link is associated with only a pair of site gates, one in each site, only those servers can route messages between the designated sites in that routing link.

Multiple routing links can be used to route messages between sites in your network for load balancing or redundancy. In this case, if you want to enforce one route over another route using link costs (for example, to specify a default link), you can change the routing-link costs to determine the route that messages take.

For example, if the cost associated with the A-B routing link is set to 3 and the cost associated with the other three routing links (B-C, B-D, and C-D) is 1, messages routed from site A to C always travel from site A to site B and then to site C. However, if the cost associated with the A-B and B-C routing links is 3 and the cost associated to the C-D and B-D routing links is 1, messages routed from site A to C always travel from site A to site B, to site D, and then to site C.

The route that a message takes to get from site A to site C depends on the costs of the routing links.

In this situation, messages routed from site A to site C always travel from site A to site B and then to site C.

In this situation, messages routed from site A to site C always travel from site A to site B, then to site D, and finally to site C.