Datasheet

Designing Organization Configuration to Meet Routing Requirements

Routing between Exchange Server 2007 and Exchange 2000/2003 is explained in Chapter 4,

“Designing and Planning Coexistence and Migrations.” Here I will focus entirely on the

Exchange Server 2007 routing technology.

Before we dig deeper into Exchange Server 2007 internal message routing, two concepts

that should be explained—namely the Exchange Server 2007 routing table and the least-cost

routing path.

The Exchange Server 2007 Routing Table

Every Exchange Server 2007 Hub Transport server calculates the routing topology based on the

Active Directory configuration that includes AD sites, AD site links, Exchange servers and their

relation to AD sites, SMTP connectors, third-party connectors, and mailbox and public folder

stores; as well as legacy Exchange 2000/2003 routing groups and connectors. This will make up

what is called the routing table.

The routing table is calculated every time the Hub Transport server is started or

when configuration changes (e.g., Active Directory change notifications) occur.

Least-Cost Routing Path

When multiple routing paths exist for a message, the routing path is calculated based on an algo-

rithm to select a single path over which the message will be routed. The following logic is used:

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Calculate the cost to the target AD site by adding all IP site link costs or connector costs

between the source and the target site. If there are multiple paths, only the path with the

lowest aggregated cost will be used.

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If there are multiple paths with the same lowest aggregated costs, the routing path with the

least hops is selected.

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If there are still multiple paths available, the site name with the lowest alphanumeric name

is selected. Starting with the site name to the target AD site, the algorithm will go backward

along the path until it finds a site name that doesn’t match.

Remember: there might be other factors like message size limits or connector

scope that can influence the least-cost routing path!

IP site link Routing group connector

Cost of IP site link Cost of routing group connector

TABLE 1.6 Internal Message Routing in Exchange Server 2007 Compared to

Exchange 2000/2003 (continued)

Exchange Server 2007 Exchange Server 2000/2003

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