In my post about the basics of DNS TTLs and caching I mentioned that DNS resolvers use the TTL of the record to determine how long to cache any particular record for. While this is /normally/ true, there are exceptions. Namely, certain public DNS resolvers have a upper limit of the TTL that they will cache. That is, if you set a TTL longer than their limit, the resolver will bring the TTL down to their limit and cache it using their TTL.Continue reading “DNS TTL Limits at Public DNS Resolvers”
Understanding DNS: TTLs and Caching
In my last post in this series I talked about common DNS record types, in this I am going to be talking about how the concept of TTLs (Time To Live) and caching are used in DNS.
The two concepts are interlinked in DNS, let’s get into it.
Understanding DNS: Common Record Types
In my last post in this series I talked about authoritative nameservers and what they do. Their function is responding to queries for domain names they are authoritative for. These queries are for specific record types; in this post I will be talking about common record types you will encounter in your use of the DNS.
For the sake of simplicity and ease of understanding I’m limiting this post to the most common record types i.e records you are most likely to encounter and use in your day-to-day use of the DNS. These are not all the record types that are available for use in the DNS.
Let’s get started.
Understanding DNS: Authoritative Nameservers
In my previous post in this series we talked about recursive resolvers and how they talk to authoritative nameservers to obtain the DNS answers they need.
In this post I want to talk about authoritative nameservers specifically.
Continue reading “Understanding DNS: Authoritative Nameservers”
Understanding DNS: Recursive Resolvers
In my last post in this series, I mentioned a kind of resolver known as a recursive resolver. In this post, I will explain what a recursive resolver is and how they work.
What is a recursive resolver?
To simply put it: A recursive resolver is a DNS resolver that resolves a DNS query by going through hierarchical sets of authoritative nameservers until it gets an answer to the query.