## ADDRESS02: Reverse DNS entry exists for name server IP address

### Test case identifier
**ADDRESS02** Reverse DNS entry should exist for name server IP address

### Objective

Some anti-spam techniques use reverse DNS lookup to allow incoming traffic.
In order to prevent name servers to be blocked or blacklisted, DNS 
administrators should publish PTR records associated to name server
addresses.

TODO: Technical reference to be found

### Inputs

The domain name to be tested.

### Ordered description of steps to be taken to execute the test case

1. Obtain the glue address records  of the domain checked
   using [Method4](../Methods.md)

2. Obtain the IP addresses of each name server of the domain checked
   using [Method5](../Methods.md)

3. For each IP address, a recursive PTR query must be performed.

4. If any answer of the queries performed in step 3 contains an RCODE
   other than NOERROR or if the answer does not include a PTR record,
   this test case fails.

### Outcome(s)

If the test case succeeds, its result is a list of addresses with corresponding
hostnames which are the result of the PTR queries performed.
The result could be represented as a hash table where the keys are the IP
addresses and the values their corresponding hostnames.

### Special procedural requirements

None.

### Intercase dependencies

The outcomes of this test is used as the input of [ADDRESS03](address03.md) test case.