Here is an example on how link state islands can occur. Figure 11 - 10 shows an Exchange Server 2007
routing group and three Exchange 2003 routing groups ??” A, B, and C. Routing Group B is a hub for
Exchange 2003 routing.
Chapter 11: Exchange Server 2007 Routing
321
Exchange Server 2007 Routing Group
(DWBGZMFD01QNBJR)
Routing Group A Routing Group C
RGC
Cost = 10
RGC
Cost = 10
Figure 11-12
Figure 11 - 12 shows clearly how now Routing Groups A and C are link state islands. Because the only
connectivity is through the Exchange Server 2007 routing group, there is no way for link state information
to flow between the Exchange 2003 routing groups.
One way to prevent or correct this problem is to add Routing Group Connectors between Routing Group
A and Routing Group C. Setting the cost to 100 prevents mail flow, but allows the sites to exchange link
state information. See Figure 11 - 13 .
Part III: Working with PowerShell in a Production Environment
322
Exchange Server 2007 Routing Group
(DWBGZMFD01QNBJR)
Routing Group A Routing Group C
RGC
Cost = 10
RGC
Cost = 100
RGC
Cost = 10
Figure 11-13
Coexistence Routing
Earlier in the chapter, the least cost routing algorithm was explored. This section looks at the impact of
Exchange 2003 coexistence on routing. The connector cost is comprised of the destination address space
as well as the site or connector cost.
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