Exchange 2000 SP2’s DSAccess Component

The suitability tests verify that the server is contactable, that it responds to queries in a timely manner, and that it offers services that DSAccess can use. The tests are in three categories: hard tests, soft tests, and side tests.

• Hard tests determine whether DSAccess can use a server. If a server fails these tests, DSAccess ignores it. For example, if a server isn't reachable through port 389 (for a DC) or 3268 (for a GC), DSAccess recognizes that the server isn't an AD server. To prevent DSAccess from connecting to an unsynchronized copy of AD and using outdated information, other hard tests determine whether the AD data on the server is synchronized and participating in typical replication activities.
• Soft tests determine the optimum servers for DSAccess to use. For example, one test determines whether a server is in the same Win2K site as the Exchange server. Other tests determine the load on the server by measuring the speed with which the server responds to LDAP queries and the number of outstanding LDAP queries. DSAccess prefers not to connect to a server that's heavily loaded because slow responses to AD queries will delay processing of messages through the routing engine. Similarly, DSAccess will avoid a server that holds an Operations or Flexible Single-Master Operation (FSMO) role for the domain or forest because such a server is also likely to be under a heavy load.
• Side tests determine whether DSAccess can use a server as a DC or GC.

If you go to an Exchange 2000 server's Properties page and select a Logging level of Minimum or higher for the Topology category of a server's MSExchangeDSAccess service, as Figure 2 shows, DSAccess reports suitability-test results in Application log event ID 2080. Figure 3 shows a sample of the information that event ID 2080 provides. You'll need a little information to interpret these results.

The servers that DSAccess discovers are divided into two groups: those that are in the same Win2K site as the Exchange server and those that are outside the site. For each server, the log shows the following results:

• The server name—for example, dbogceu01.emea.cpqcorp.net.
• The roles that the server can fulfill. D indicates that the server is a DC, G indicates a GC, and C means that the server is acting as the configuration DC. CDG means that the selected server can fulfill all three roles.
• Whether the server is reachable. This value is a bit mask. A value of 0 indicates that the server is unreachable and that DSAccess can't use it. A value of 1 means that the server is reachable as a GC through port 3268, 2 means that it's reachable as a DC through port 389, and 4 means that the server can act as a configuration DC (also through port 389). A value of 7 (1 + 2 + 4) indicates that the server is reachable through all ports and can act in any role.
• Whether the server is synchronized. A value of 1 means that the GC is synchronized, a value of 2 means that the DC is synchronized, and a value of 4 indicates that the configuration DC is synchronized. A value of 7 means that all possible synchronization has taken place.
• Whether the server is capable of acting as a GC. A value of 1 indicates that the server can be a GC; 0 indicates that it can't.
• Whether the server is the PDC emulator for a domain. A value of 0 indicates that the server isn't a PDC emulator; 1 indicates that it is.
• Whether the server passes the system ACL (SACL) test. The SACL test determines whether the server resides in a domain that you've prepared for Exchange 2000 by running the DomainPrep part of the Exchange 2000 installation program. A value of 1 indicates that the server passes the SACL test; 0 indicates that it doesn't.
• Whether the server hosts crucial data. A value of 1 indicates that the Microsoft Exchange container exists within the configuration naming context (NC) on this DC; a value of 0 indicates that it doesn't. The Exchange container stores crucial data (e.g., server names, routing group information, connectors) that must be available for routing to work. DSAccess won't select a DC that doesn't host this container.

A Valuable Upgrade
DSAccess is a crucial Exchange 2000 component that servers and clients alike rely on. In SP2, Microsoft has done a good job of understanding the problems with the early version of DSAccess and responding with an upgraded version—DSAccess on steroids. The only pity is that we waited longer than a year to get the new code. If you aren't sure whether to upgrade servers to SP2, DSAccess provides reasons to move as quickly as possible, especially if you operate large or distributed Exchange 2000 environments.