Common resource record types and application examples

The following is from the author of the "network administrator must read-Net Formation" (2nd edition) of the book.   7.6.2 main resource record types and application examplesAfter you create a zone, you need to add additional resource records to the zone. The most common resource records (RRS) to add include the following.

N Host (A): Used to map DNS domain names to the IP addresses used by the computer. N Alias (CNAME): used to map the alias of a DNS domain name to another primary or canonical name. N Mail Exchanger (MX): The name of the computer used to map DNS domain names to exchange or forward messages. n Pointer (PTR): A reverse DNS domain name that is used to map the IP address of a computer that is based on its forward DNS domain name. N service location (SRV): Used to map DNS domain names to a specified list of DNS hosts that provide specific services such as Active Directory domain controllers. The following is a brief introduction to the roles and basic configuration methods of the above 5 major resource records.

1. Host (A) resource record (ARR)

ARR is the host address (A) resource record. It is responsible for mapping DNS domain names to the 32-bit addresses of version 4 of Internet Protocol (IP). The syntax format is: Owner class TTL A ip_v4_address (where the TTL field value is omitted).

For example: Grfw-s1. Grfwgz.local. In A 192.168.0.1 (note that the period (.) after the domain host FQDN is not less, the same below).

Host (A) resource records are used in zones to associate DNS domain names of computers (or hosts) with their IP addresses, and can be added to zones in multiple ways. n using the DNS console, you can manually create a resource record for a static TCP/IP client. To open the dialog shown in Figure 7-38, click the right mouse button in the corresponding forward lookup zone in the DNS console and select New Host in the pop-up menu. The appropriate host name and IP address can be configured here.

The

  Diagram 7-38  The new Host dialog box   The Create associated pointer (PTR) record option in it specifies whether to create a pointer (PTR) resource record for that host in the reverse lookup zone. This operation allows the DNS client to resolve the host IP address to its associated name. If this option is selected, the DNS console constructs an associated PTR resource record in the existing reverse lookup zone using the information specified above for the hostname and IP address. Note, however, that in order to create a pointer (PTR) resource record, the reverse lookup zone must already exist on a DNS server in the IN-ADDR.ARPA domain, otherwise the reverse lookup zone is created first. If you selected the "Allow all authenticated users to update the DNS records with the same owner name" option, specify that any authenticated client can update the resource record. This option applies to any additional resource records created using the name specified by the current record, which is displayed in the Name column of the DNS console. This option applies the ACL to the resource record, which can be modified in the security settings of the resource record. This setting applies only to resource records for zones that are stored in Active Directory. n         when IP configuration changes, Windows clients and servers use the DHCP Client service to dynamically register and update their A resource records within DNS. n         If you are running an earlier version of the Microsoft operating system and DHCP-enabled clients obtain their IP leases from a qualified DHCP server, You can register and update a resource record with a proxy (currently only Windows 2000 and Windows Server 2003 DHCP Server services support this feature).

Not all computers require host (A) resource records, but computers that share resources on a network require that record. Any computer that shares resources and needs to be identified with its DNS domain name needs to use A resource record to provide DNS name resolution for the IP address of the computer. Most of the ARR needed in the zone can include workstations or servers for other shared resources, other DNS servers, mail servers, and WEB servers. These resource records consist of most of the resource records in the zone database.

2. Alias (CNAME) resource record (Cnamerr)Cnamerr is a canonical name (CNAME) resource record. Map the alias or alternate DNS domain name in the Owner field to the standard or primary DNS domain name specified in the Canonical_name field. The standard or primary DNS domain name used in this data is required and must be resolved to a valid DNS domain name in the namespace. The syntax format is: Owner TTL class CNAME Canonical_name for example: aliasname.example.microsoft.com. CNAME truename.example.microsoft.com.

Alias (CNAME) resource records allow you to use multiple names to point to a single host, making certain tasks easier to perform. For example, to maintain an FTP server and a Web server on the same computer, you can use the server name (FTP, WWW) of the server that hosts these services by using the Cnamerr mapped to the DNS host name (such as GRFW-S1). Adding Cnamerr is similar to adding arr, but it can be created in the forward lookup zone as well as in the reverse lookup zone. Right-click in the appropriate lookup area, select the new Alias command from the pop-up menu, and open the dialog shown in Figure 7-39. Enter the alias of the corresponding record and the fully qualified domain name of the target host respectively. The check features and configuration methods in the dialog box are the same as the corresponding check features in the ARR records described earlier. Figure 7-39 the alias (CNAME) tab of the New Resource Record dialog box recommends that Cnamerr be used in the following situations.

n when the host specified in the arr of the same zone needs to be renamed. n when used for common names of known servers such as WWW needs to resolve a set of separate computers that provide the same services (each with a separate arr). For example, a set of redundant Web servers. When you rename a computer by using an existing arr in a zone, you can temporarily use Cnamerr to allow users and programs to use the grace period to convert from specifying the old computer name to using the new name. To do this, the following actions are required.

(1) For the new DNS domain name of the computer, the new arr will be added to the zone. (2) for the old DNS domain name, the cnamerr that points to the new arr is added. (3) Remove the old DNS domain name from the zone (and, if appropriate, the original arr of the associated ptrrr).

When you use Cnamerr to define an alias or rename a computer, temporary restrictions are set on the time that records are used in the zone before the record is deleted from DNS. If you forget to delete Cnamerr and later delete the ARR associated with it, then Cnamerr may try to parse queries that are no longer used on the web, thereby wasting server resources.

The most common use of cnamerr is to provide a permanent DNS domain alias to an IP address used by multiple computers or Web servers for common name resolution based on a service name such as www.example.microsoft.com. The following example shows how to use the basic syntax of Cnamerr. Alias_name in CNAME primary_canonical_name below to give an example to explain. In the following example, a computer named "host-a.example.microsoft.com" needs to be used simultaneously to serve as a Web server named "www.example.microsoft.com" and " Ftp.example.microsoft.com "FTP server. To implement the intended purpose of naming the computer, you can add and use the following CNAME items in the example.microsoft.com zone.

Host-a in a 10.0.0.20 ftp in CNAME host-a www. CNAME hos T-a If you later decide to move the FTP server to another computer that is independent of the Web server on Host-a, Simply change the cnamerr in the zone for ftp.example.microsoft.com and add additional arr to the area of the new computer that hosts the FTP server. Based on the above example, if the new computer is named Host-b.example.microsoft.com, the new and modified A and Cnamerr records are as follows.

Host-a in a 10.0.0.20 host-b on a 10.0.0.21 ftp in CNAME Host-b www. CNAME host-a 3. The Mail exchanger (MX) resource record (MXRR) MX RR is a mail exchanger (MX) resource record. As specified in Mail_exchanger_host, it provides message routing for the Mail exchanger host to send the message to the domain name specified in the Owner field. A 2-digit preference value indicates the preferred order in cases where multiple exchanger hosts are specified. Each switch host must have a corresponding host (a) address resource record in the active zone. The syntax format is: Owner TTL class MX preference Mail_exchanger_host

For example: example.microsoft.com