Continuing our glossary of DNS tips & tricks, we’re covering the letters P (for PTR), Q (for quotes), and R (for reverse DNS) this time.
Jan 23rd, 2020
Continuing our glossary of tips & tricks from the Men&Mice DNS training archives, we’re covering the letters P, Q, and R this time.
PTR records, used in reverse DNS zones (see below) are essentially reverse A (or AAAA, if you run IPv6 — good for you!) records: where the latter connects domain names to IP addresses, PTR records connect IP addresses to domain names.
A/AAAA record: localhost —> 127.0.0.1/::1
PTR record: 127.0.0.1/::1 —> localhost
If you’ve ever run a mail server, you likely heard about (and had to configure) PTR records. Mail servers identify spam emails by, among other things, mismatched A/AAAA records or missing PTR records for the sender’s hostname.
You thought it was for ‘query’, didn’t you? But that’d be too easy.
When you edit DNS records that contain spaces (such as SPF or TXT records) the record value needs to be enclosed in quote marks: “”
In today’s modern interfaces used to edit DNS records (hint-hint Men&Mice Suite ????) this isn’t something you’re likely to encounter, as the software takes care of adding the syntax as specified in RFC 1035. But DNS, at the end of the day, is parsed in plaintext, and so it’s useful to keep in mind in case you find yourself without an abstraction tool.
Reverse DNS zones are to DNS zones what PTR records are to A/AAAA records. Instead of a normal query that translates a domain name to an IP address, it translates the IP address to its corresponding hostname.
There are a number of uses for reverse DNS zones, such as:
This series consists of small pieces of interesting information — but a lot more can be said and done. To learn more in-depth about DNS specifically, we offer a comprehensive DNS training program.
You can enroll in different groups depending on your skill level:
Check out our training calendar for 2020, and reach out to us with any questions.