DNS propagation - the process

Question

I am not a network person, so, I'm not sure how to ask this question. Let's say we have our own DNS server that is local to our company. Someone registers a new domain name or a change is made to DNS records and the authoritative name servers have been updated.

How does our local DNS server know about the new domain name or a change to an existing domain name? I mean, a request has to come from our local network in order for our local DNS to even know about the name, right? It's not like authoritative name servers push information to every DNS server automagically.

Am I'm correct that requests have to come from our local DNS servers in order for the local records to be updated? And does that mean the only way our DNS servers will be updated is when a request is made for a domain name by a user?

thx

Couldn't you type "How does DNS work" into google ? – user9517 Feb 21 '14 at 19:13 — user9517, Feb 21 '14 at 19:13
You could even have searched ServerFault with the same text – user9517 Feb 21 '14 at 19:15 — user9517, Feb 21 '14 at 19:15

score -1 · Answer 1 · answered Feb 21 '14 at 20:12

To simplify your question, there are a couple things to keep in mind.

DNS = Domain Name System

Name Servers = Stores DNS records to resolve domains

On your local computer, you have a DNS resolver that connects you to the global DNS network. Most recently and commonly, you can use Google's public DNS servers at:

8.8.8.8 and 8.8.4.4

When your computer needs to resolve a hostname like google.com, it will first send a generic request to your locally set DNS resolver. That would look like this in a Windows command prompt:

C:\Users\JacobN>nslookup google.com
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non-authoritative answer:
Name:    google.com
Addresses:  2607:f8b0:4004:802::1008
          74.125.228.71
          74.125.228.66
          74.125.228.72

You get a Non-authoriatative answer back, because the name server we just queried doesn't maintain the records for Google, it simply has them cached for us.

You can use the set q=NS command after starting nslookup to query a domain name's authorative name servers:

C:\Users\JacobN>nslookup
Default Server:  google-public-dns-a.google.com
Address:  8.8.8.8

> set q=NS
> google.com
Server:  google-public-dns-a.google.com
Address:  8.8.8.8

Non-authoritative answer:
google.com      nameserver = ns2.google.com
google.com      nameserver = ns4.google.com
google.com      nameserver = ns3.google.com
google.com      nameserver = ns1.google.com

Now your computer can also directly query one of the authoritative name servers, to get back an authoritative response:

C:\Users\JacobN>nslookup google.com ns1.google.com
Server:  ns1.google.com
Address:  216.239.32.10

Name:    google.com
Addresses:  2607:f8b0:4004:806::1008
          74.125.228.194
          74.125.228.193
          74.125.228.201

Now if Google was to update their DNS records on their ns1.google.com name server, it could take between 1-8 hours typically for those records to propagate over to other caching name servers.

So to answer your question, your local DNS server knows how to resolve your domain name, because when you registered your domain name you had to point the name server records to a valid DNS server, making that DNS server (name server) the authoritative server for your domain's DNS queries.

All other name servers on the net, such as Google's 8.8.8.8 will cache your server's response as people search for your domain name. A good example is that your local ISP could be caching DNS queries. For instance if your next door neighbor just got the authoritative DNS records returned for your domain, and then you looked them up right after, more than likely you'll get a cached response from your ISP's name servers rather than the request having to possibly break out of the network just to receive back the same results a minute later.

If no one in asks for your domain name over a 24 hour period, it could be possible for the DNS records to decay and fall out of cache based on their TTL (Time to Live) setting. If this was the case, when someone went to query your domain again, the first thing that would happen would be a whois lookup on your domain seeing what the authoritative name servers are for the domain, and then you'd be getting an IP address resolved back from your local DNS server that you've setup to handle those requests.

Name servers and DNS are a pretty complex topic, if you need any further explanations let me know, as I've written extensively about them:

http://www.inmotionhosting.com/support/domain-names/dns-nameserver-changes/what-is-a-name-server

DNS propagation - the process

1 Answers1