DNS on Windows Server 2003, 3rd Edition

Subnetting on an Octet Boundary

Since Movie U. has just three /24 (Class C-sized) networks, one per segment, there’s no particular need to subnet those networks. However, our sister university, Altered State, has a Class B-sized network, 172.20/16. Their network is subnetted between the third and fourth octet of the IP address; that is, their subnet mask is 255.255.255.0. They’ve already created a number of subdomains of their domain: altered.edu, including fx.altered.edu (okay, we copied them); makeup.altered.edu; and foley.altered.edu. Since each of these departments also runs its own subnet (their Special Effects department runs subnet 172.20.2/24, Makeup runs 172.20.15/24, and Foley runs 172.20.25/24), they’d like to divvy up their in-addr.arpa namespace appropriately, too.

Delegating in-addr.arpa subdomains is no different from delegating subdomains of forward-mapping domains. First, they or their departments create three new zones, 2.20.172.in-addr.arpa, 15.20.172.in-addr.arpa, and 25.20.172.in-addr.arpa. The 20.172.in-addr.arpa administrators also need to add the NS records with the New Delegation Wizard, as we described in the fx.movie.edu example earlier in this chapter. Figure 10-7 shows how the second screen of the New Delegation Wizard would look when adding delegation to the 2.20.172.in-addr.arpa zone:

Figure 10-7. Adding reverse-mapping delegation using the New Delegation ...