Saturday, August 22, 2020

DNS - Domain Name System



DNS or Domain Name System is like a phonebook for the internet. It translate human readable computer hostnames into IP addresses. This process is called DNS name resolution.

For your internet connection, normally you'll use the DNS provided by your ISP (Internet Service Provider), or you can specify your desired DNS. Go to your network connection settings, if you don't see DNS settings there, try to find in advance settings. There was once I remember the default DNS was unable to serve my requests. I Googled and found the workaround, is by using Google public DNS. If you are interested to change it, try 8.8.8.8 for DNS server.

When a request is made, the DNS resolver will send the request to a DNS root nameserver, where it responds with TLD (Top Level Domain : .com / .net) nameserver based on the request. Say, the request is for kdb.jcrys26.com. The request will be redirected to .com TLD nameserver. The TLD server will then responds with the IP of for jcrys26.com's nameserver. A query then will be sent to the domain nameserver, where then the target IP address will be returned. Maybe a diagram would be easier to illustrate this, but I don't feel like draw it today.

If I directly try to access the IP, instead of the URL, will I be able to skip the DNS servers? I tried with kdb.jcrys26.com, using nslookup commands, I got this.

$ nslookup kdb.jcrys26.com
Server:		8.8.8.8
Address:	8.8.8.8#53

Non-authoritative answer:
kdb.jcrys26.com	canonical name = ghs.google.com.
Name:	ghs.google.com
Address: 216.58.196.51


However, http://216.58.196.51 doesn't give the same result as http://kdb.jcrys26.com. But it does give the same result for the canonical name (http://ghs.google.com). I guess this is how the Blogger is setup to use custom domain make it work differently. It should be a common IP that serves for all blogger redirects. I remember there're some other parameter I need to set for this "redirect". :P Check out the further reads section for how browser parses IP address.

Speaking of DNS, I now can hardly remember how we do the DNS handling and IP warming in our MTA (Mail Transfer Agent) in order to setup for sending our client marketing emails to subsribers. Probably I have it somewhere in my work logs. :P Anyway, here I attached the nslookup examples from The Geek Stuffs below for further reads as well.

Further reads:

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