Difference between DNS A Record & Glue Record

In last two post we’ve discussed details about DNS glue record and how to check it using bind-utils. A last bit of confusion may left as both A and Glue record point a domain or sub-domain to an IP address. This post will clarify that.

Similarity:

  1. Both of them point a domain to an IP address
  2. Upon receive IP address client use that for retrieving data or for further quarry.

Differences: 

  1. ‘A’ record corresponds to the IP address of the host of a domain whereas ‘Glue Record’ corresponding to IP address of authoritative nameserver only.
  2. ‘Glue Record’ is used to break circular dependency in name resolution for using sub domain as nameserver of the primary domain, whereas ‘A’ record simply define the host of a domain.
  3. ‘A’ record comes in “Answer” section of DNS reply whereas ‘Glue Record’ comes in “Additional” Section of DNS reply.
  4. ‘A’ record is returned by Authoritative nameserver only, whereas ‘Glue Record’ is Returned by TLDs nameserver.
  5. Authoritative nameserver returns ‘A’ record only for the quarried domain like if you quarry A record for interentry.com, you’ll get back exactly the IP address of interentry.com. On other hand TLD’s nameserver returns Glue Record IP address of the sub-domain nameserver, which is in use for the primary domain, in return of a DNS quarry seeking any record like A, MX, TXT or whatever it is. Like if you quarry .com’s nameserver for MX record of interentry.com you’ll be returned with NS record of interentry.com along with ‘Glue Record’ corresponding to the nameserver sub domain.

Hope the three post (last two and this one) about Glue Record will clear any ambiguity left while using sub domain as nameserver of the primary domain. For any other confusion please write admin[at]serverlog[dot]net

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