Table 6.3 shows how to configure your network with each type of subnet.Table 6.3 Planning Reverse Lookup Zones Windows 2000-based clients and Windows 2000 DHCP servers can automatically add PTR resource records, or you can configure PTR resource records at the same time as when you create A resource records; otherwise, you might want to add PTR resource records manually.
To add PTR resource records Many organizations divide class C networks into smaller portions.
This process is referred to as "subnetting a network." If you have subnetted a network, you can create corresponding subnetted reverse lookup zones, as specified in RFC 2317.
Subdomains do not need to have their own reverse lookup zones.
If you have multiple class C network identifiers, for each one you can configure a reverse lookup zone and PTR resource records on the primary name server closest to the subnet with that network identifier.
Reverse lookup zones and PTR resource records are not necessary for Active Directory to work, but you need them if you want clients to be able to resolve FQDNs from IP addresses.
Also, PTR resource records are commonly used by some applications to verify the identities of clients.The following sections, explain the syntax of classless reverse lookup zones and describe how to delegate and configure reverse lookup zones by using the preceding example.For more information about delegating reverse lookup zones, see the Request for Comments link on the Web Resources page at .The following sections explain where to put reverse lookup zones and how to create, configure, and delegate them.For information about any of the IP addressing concepts discussed in the following sections, see "Introduction to TCP/IP" in this book.If you own one class C address, and you want to distribute the addresses in the range to several different groups (for example, branch offices), but you do not want to manage the reverse lookup zones for those addresses, you would create classless reverse lookup zones and delegate them to those groups.