day03

Day 03 of 90

In our previous session, we discussed HTTP and its role in Websites. Today, we will have a look at what DNS is and why is it important.

Intro

I'm pretty sure I speak for everyone when I say that it is easier to find your friends number in your phonebook by searching their name rather than having to remember their phone number. DNS is the phonebook of the internet. It maps domain names to the respective IP addresses, so that users dont have to remember the complex IP address of websites and just remember the domain names instead. Web servers where websites are hosted have addresses known as IP addresses to identify them (an example is google.com whose IP address is 172.217.170.206). You can copy and paste the adress directly into your browser and you will be taken to Google's home page.

Since the addresse are really complex, DNS helps us by giving us the chance to remeber the domain (google.com) instead of the very complex numbers. It takes care of translating the domain names into their respective addresses. Cool Right?

Resources

1. What is a domain name
2. What is DNS
3. How does DNS work
4. Youtube
5. Google
6. Mess with DNS - DNS playground
7. How DNS works (comic)
8. DNS records
9. Glue Records
10. All about DNS records
11. Authoritative v/s Recusive DNS servers

Learning objectives

After going through the above resources, you should be able to explain the following concepts to a five year old

• What is a domain
• The parts of a domain name
• Difference between domain name and URL
• What the heck is DNS and how does it work
• The DNS query pipeline
• Recusive DNS lookup VS iterative lookup
• The four servers involved in a DNS lookup ( assuming the address is not cached)
• What is a CNAME record
• How does resolution for subdomains happen?
• What is DNS caching
• What are A records
• What are MX records
• What are TXT records and some examples of it
• What are NS records
• Security concerns associated with DSN

Wrapping up

• DNS is the phonebook of the internet

• Nameservers make up the DNS, they hold dns records and map domain names to IP addresses

• The four DNS servers are

  • DNS resolver (operated by the ISP) which is like the midleman between the end user and the other DNS servers. It also checks for cached records, and caches and stores results of DNS queries
  • Root Nameserver - Theres really not alot of these, around 13 or so in the whole world
  • TLD Nameserver
  • Authoritave Nameserver - This stores the actual domain records

• DNS records ares instructions living in the authoritative nameserver that provide information about a domain.Some of the most common DNS records include:

  • A record - For IP address lookup and DNSBL(more on this letter). Thanks to this, we can visit websites we dont even know their IP addresses :)
  • AAAA record - It's like the A record, except is points to the IPv6 addresses
  • CNAME record - Which points a domain name (alias) to another domain name. Mostly used in subdomains
  • NS record - Specifies the authoritative nameserver for a domain
  • MX record - Specifies where the emails for a domain should be routed, making it possible to direct emails to a mail server
  • TXT records - For verification and security. Include SPF records and DKIM records which helps identify your domain as a trusted source for email systems. This helps your emails from being treated as spam

• Just to mention some security concerns with DNS (They are beyond the scope of this session and we will not look at them in detail)

  • DNS reflection and amplification attacks
  • Typosquating
  • DNS cache poisoning

Thats it for today, see you in the next session