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This mode requires a third database instance termed a witness. The witness server verifies whether the principal server is functioning. The mirror server initiates automatic failover when the mirror and witness remain connected but neither can contact the principal server.

Figure 5-22

You use NS resource records to specify the authoritative name servers for a given zone. The NS resource record of the first primary server of a zone is configured automatically.

static void Main(string[] args)

5-34

5

Role switching involves transferring the principal role to the instance functioning as a mirror. The mirror server takes over the principal role and brings its copy of the database online as the new principal. The former principal server assumes the mirror role. Role switching can take the following three forms:

The following line is an example NS record taken from the database file for the luc ernepublishing.com zone:

Console.WriteLine( Reading one line of the boot.ini file: ); StreamReader sw = new StreamReader(@"C:\boot.ini ); Console.WriteLine( First line of boot.ini: + sw.ReadLine()); }

In this record, the @ symbol represents the zone defined by the SOA record in the same zone file. The complete entry, then, effectively maps the lucernepublishing.com domain to a DNS server hosted on a computer named dns1.lucernepublishing.com.

Exam Tip In primary zones, zone transfers by default are allowed only to servers specified on the Name Servers tab. This restriction is new to Windows Server 2003.

6-42

You use the WINS tab, shown in Figure 5-23 or the WINS-R tab in reverse lookup zones to configure Windows Internet Name Service (WINS) servers to aid in name resolution for a given zone after DNS servers have failed to resolve a queried name.

Figure 5-23

the high-safety mode is configured. (See the explanation of high-safety mode with automatic failover mentioned earlier.)

Exam Tip When you configure WINS lookup for a forward lookup zone, a WINS resource record pointing to the WINS server you specify on the WINS tab is added to the zone database. When you configure WINS-R lookup for a reverse lookup zone, a corresponding WINS-R resource record is added to the zone database.

6

5-35

The Zone Transfers tab, shown in Figure 5-24, allows you to restrict zone transfers from the local master server. For primary zones, zone transfers to secondary servers by default are either completely disabled or limited to name servers configured on the Name Servers tab. The former restriction applies when the DNS server has been added by using the Manage Your Server window; the latter, when it has been added by using the Windows Components Wizard. As an alternative to these default restrictions, you can customize zone transfer restrictions by selecting the Only To The Following Servers option and then specifying the IP addresses of allowed secondary servers in the list below this option. Secondary zones by default do not allow zone transfers to other secondary zones, but you can enable this feature simply by selecting the Allow Zone Transfers check box.

Figure 5-24

<Assembly: FileIOPermissionAttribute(SecurityAction.RequestOptional,

modes. It can force service if the principal server has failed and the mirror is available. This role switch carries with it the possibility of data loss.

Off the Record In Windows 2000, the default setting on the Zone Transfers tab for primary zones was to allow transfers to any server, but this feature created an unnecessary security hole. Think about it: why would you want to enable anyone who can access your DNS server to set up a secondary server and peruse your network s resource records Restricting zone trans fers by default is a lot smarter it allows you to prevent unauthorized copying of zone data.

Notification The Zone Transfers tab also allows you to configure notification to sec ondary servers. To perform this task, click Notify on the Zone Transfers tab when zone transfers are enabled. This action opens the Notify dialog box, as shown in Figure 5-25, in which you can specify secondary servers that should be notified whenever a zone update occurs at the local master server. By default, when zone transfers are enabled, all servers listed on the Name Servers tab are automatically notified of zone changes.

5-36

<Assembly: FileIOPermissionAttribute(SecurityAction.RequestRefuse,

9-45

For more information about database mirroring, consult the following article on MSDN: msdn2.microsoft.com/en-us/library/ms189852.aspx.