DNS : SERVFAIL when resolving PTR records

[the-nando]

Overview of the Issue

The current implementation of the DNS PTR records resolver iterates through all services and nodes and, if nothing is found, proceeds to call the function which handles recursion without checking if recursion is desired (rd flag) and if we have recursors configured.
This causes two issues:

• PTR queries for non-existent IPs return SERVFAIL instead of NXDOMAIN as we end up here.
• Request without the rd flag set are recursed.

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Reproduction Steps

Issue with calling handleRecurse if not neeed:

• Start Consul without recursors configured
• dig -p 8600 -x 127.0.0.3 @localhost
  It should return NXDOMAIN but returns SERVFAIL and in the logs:

2024-01-31T08:47:14.946Z [ERROR] agent.dns: all resolvers failed for question from client: question="{3.0.0.127.in-addr.arpa. 12 1}" client=127.0.0.1:41033 client_network=udp

Issue with lack of handling of the rd flag:

• Start Consul with recursors = ["1.1.1.1"] configured
• dig -p 8600-x 1.1.1.1 @localhost +norecurse
  It should return NXDOMAIN but returns one.one.one.one.