Chris's Wiki :: blog/sysadmin/DNSRepliesWhereNSRecordsShowUp

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2024-05-15 04:30:04

Suppose, not hypothetically, that you're trying to check the NS records for a bunch of subdomains to see if one particular DNS server is listed (because it shouldn't be). In DNS, there are two places that have NS records for a subdomain; the nameservers for the subdomain itself (which lists NS records as part of the zone's full data), and the nameservers for the parent domain, which have to tell resolvers what the authoritative DNS servers for the subdomain are. Today I discovered that these two sorts of DNS servers can return NS records in different parts of the DNS reply.

(These parent domain NS records are technically not glue records, although I think they may commonly be called that and DNS people will most likely understand what you mean if you call them 'NS glue records' or the like.)

A DNS server's answer to your query generally has three sections, although not all of them may be present in any particular reply. The answer section contains the 'resource records' that directly answer your query, the 'authority' section contains NS records of the DNS servers for the domain, and the 'additional' section contains potentially helpful additional data, such as the addresses of some of the DNS servers in the authority section. Now, suppose that you ask a DNS server (one that has the data) for the NS records for a (sub)domain.

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