单选题An administrator needs to configure a server to restrict mail traffic to an application server for security reasons.  Which of the following techniques can be used to manage this？（）APATBACLsCSubnet maskingDPort blocking

正确答案：A
解析：Explanation: SQL Server 2000 failover clustering provides high availability support by allowing us to configure one failover cluster to automatically, with no manual configuration, fail over to any other node in the failover cluster configuration. In this way, we minimize system downtime and provide high server availability during an operating system failure or a planned upgrade. Before SQL Server 2000 failover clustering can be set up, we must install Windows NT 4.0, Enterprise Edition, Windows 2000 Advanced Server or Windows 2000 Datacenter Server, and the Microsoft Cluster Service (MSCS).

In this scenario a cluster would be preferred to a standby server because it would be available immediately. A standby server on the other would require manual configuration and more time to become online.

Incorrect Answers:
B: A standby server would require you to reconfigure clients to allow it to connect to the standby server when the main server goes down. It would require at least several minutes of manual administration before the standby server would be operational. But the scenario requires that no reconfiguration of the client computers should be necessary. Therefore we should use a SQL Server 2000 cluster not a standby server.

Note: A standby server is a second server that contains a copy of the databases on the primary server and that can be brought online in the event of a primary server failure or due to scheduled maintenance on the primary server. This allows users to continue working with databases when the primary server becomes unavailable. When the primary server becomes available again, any changes to the standby server's copies of databases must be restored back to the primary server.

C: The Microsoft Distributed Transaction Coordinator coordinates distributed transactions, but would not increase availability.

Note: The Microsoft Distributed Transaction Coordinator (MS DTC) is a transaction manager that allows client applications to include several different sources of data in one transaction. MS DTC coordinates committing the distributed transaction across all the servers enlisted in the transaction.

An installation of SQL Server 2000 can participate in a distributed transaction by calling stored procedures on remote servers running SQL Server, automatically or explicitly promoting the local transaction to a distributed transaction and enlist remote servers in the transaction, and making distributed updates that update data on multiple OLE DB data sources. If these OLE DB data sources support the OLE DB distributed transaction interface, SQL Server 2000 can also enlist them in the distributed transaction. The MS DTC service coordinates the proper completion of the distributed transaction to ensure that either all of the updates on all the servers are made permanent, or, in the case of errors, all erased.

D: With Federated SQL Server 2000 servers, SQL Server 2000 databases can be spread across a group of autonomous database servers. These are capable of supporting the processing growth requirements of the largest Web sites and enterprise data-processing systems built with Microsoft Windows DNA, which divides the processing units of a data processing system into logical tiers. This however does not improve availability.

参考答案：C

参考答案：B

参考答案：B