If the DNS server for your Domain goes down the records should still be saved in all the other DNS servers around the world. They will stay the same as they were before you domain's DNS server wen't down. While your DNS server is down you won't be able to change where the Domain points. While your registration server is down you will not be able to transfer or sell your domain.
this post was submitted on 20 Jun 2023
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Correct, but not the whole story.
If your registrar goes down, and you have your authoritative DNS anywhere else, then literally nothing happens. They just register the domain for you and give you an interface to pass your 'glue' records up to the TLD root servers.
If those glue records point to on-site DNS, or anything that is not your registrar's DNS servers, then your registrar being down is inconsequential other than that you would not be able to update your glue records, or renew your domain.
A separate question of "what happens if my authoritative servers go down", is answered above.
The two are not one in the same, though they can be.
You should actually be able to transfer and sell - that's handled at the tld.
Also, there's a lifetime to that cache, so if it's down long enough it'll become unreachable.
I've never really understood the whole TTL thing. Will the domain essentially point to nothing if the TTL runs out while the DNS server is down or will it default to older record?
The record will expire and, in this scenario, effectively become non-existent.
Once upon a time TTLs we’re rather long so temporary outages were less impactive. These days TTLs of less than a minute are common to accommodate redundancy. It doesn’t do want good to have redundant systems if DNS keep pointing at the downed system during an outage.
Your domain is "hosted" (in this context, the DNS entries, not the actual content) on one or, ideally, more DNS servers that are known as the authoritative servers for your domain. You can look those up by searching the SOA (start of authority) and NS (nameserver) records for it.
Downstream servers may keep those and other records in cache for a while, usually guided by the TTL (time to live) entry. Once that expires, however, they need to refresh the data from the authoritative servers.
When those are unreachable, that cannot do so, and your domain is de facto unreachable for the internet at large, regardless of your own server actually being up.
You can still reach them by surfing to the actual IP instead, and/or hardcoding the DNS name in your local hosts file or your local DNS server/resolver. That is, of course, not visible to the internet at large.
You could host your own DNS servers to mitigate somewhat, but keep in mind that every level above your domain also needs to know which server is authoritative - my tuxera.be used to be self hosted, so the .be root servers had to know what the SOA for tuxera was.
Honestly, it's not something to worry about. I didn't keep up with changes in DNS security, so i switched to route53 (Amazon). I've been considering switching again to hetzner.de where i have some servers anyway.
DNS is pretty lightweight (relatively speaking), so it's probably the last thing to go down if a registrar is in trouble; you'd have plenty of warning signs beforehand.
(Yes, for pedantry, technically a registrar doesn't even have to offer DNS at all, they just handle ownership and administration at the top level domain, but most do anyway)
If the registrar goes down that means you will not be able to change your NS and glue records with the TLD (com.).
If you are also using your registrar's authoritaive DNS servers and those are down, it means your website will likely be entirely unreachable regardless of what recursive DNS servers someone is using. If you are using someone else's authoritative DNS servers (such as Cloudflare, Route53, Dyn, Google Cloud, etc.) your registrar going down would not cause immediate problems.
If Google recursive DNS servers go down, it means anyone using those servers will be unable to find any website they wish to visit, including yours. Basically as far as most normal users would be able to tell their internet just stops working. There are many popular options for public recursive DNS including Google (8.8.8.8), Cloudflare (1.1.1.1), Quad9 (9.9.9.9), OpenDNS, AdGuard, and more. Not all recursive DNS operators host authoritative servers, and if they do the infrastructure for the two services are often different because they have different uses and needs.
Google's 8.8.8.8 servers are recursive, they do not host the data, they only look it up and cache it. The recursive servers talk to the authoritative servers. This is what a recursive DNS server does when you try to visit example.com. assuming it doesn't have any of this data cached:
- Figures out where
com.'s DNS servers are by querying the special root zone (.) DNS servers (that are expected to be known by all recursive DNS servers and change incredibly infrequently) for the NS records forcom.. The root zone DNS servers may also respond with "glue" records indicating the IP addresses of thecom.DNS servers. - Figures out where
example.com.'s DNS servers are by querying the DNS servers found in step 1 for the NS records forexample.com.. Thecom.'s DNS servers may also respond with "glue" records indicating the IP addresses of theexample.com.DNS servers. - Figures out what IP address(es) host
example.com.by querying the DNS servers found in step 2 for theAand/orAAAArecords forexample.com.