2.4. Prerequisite Section

This section contains a set of RRset prerequisites which must be satisfied at the time the UPDATE packet is received by the primary master server. The format of this section is as specified by [RFC1035 4.1.3]. There are five possible sets of semantics that can be expressed here, summarized as follows and then explained below.

1. RRset exists (value independent). At least one RR with a specified NAME and TYPE (in the zone and class specified by the Zone Section) must exist.

2. RRset exists (value dependent). A set of RRs with a specified NAME and TYPE exists and has the same members with the same RDATAs as the RRset specified here in this Section.

3. RRset does not exist. No RRs with a specified NAME and TYPE (in the zone and class denoted by the Zone Section) can exist.

4. Name is in use. At least one RR with a specified NAME (in the zone and class specified by the Zone Section) must exist. Note that this prerequisite is NOT satisfied by empty nonterminals.

5. Name is not in use. No RR of any type is owned by a specified NAME. Note that this prerequisite IS satisfied by empty nonterminals.

The syntax of these is as follows:

• 2.4.1. RRset Exists (Value Independent)
• 2.4.2. RRset Exists (Value Dependent)
• 2.4.3. RRset Does Not Exist
• 2.4.4. Name Is In Use
• 2.4.5. Name Is Not In Use