What is DNS?
DNS (Domain Name System) provides a simple way for us to
communicate with devices on the internet without remembering complex numbers.
Much like every house has a unique address for sending mail directly to it,
every computer on the internet has its own unique address to communicate with
it called an IP address. An IP address looks like the following 104.21.56.127,
4 sets of digits ranging from 0 - 255 separated by a period. When you want to
visit a website, it's not exactly convenient to remember this complicated set
of numbers, and that's where DNS can help. So instead of rememberin104.21.56.127, you can remember
hackingtruth.org instead. DNS in full details
|
google.com |
|
nasa.gov |
|
hackingtruth.in |
104.21.56.127 | bbc.co.uk |
|
hackingtruth.org |
|
facebook.com |
|
twitter.com |
Domain Hierarchy
TLD (Top-Level Domain)
A TLD is the most
righthand part of a domain name. So, for example, the google.com TLD is .com.
There are two types of TLD, gTLD (Generic Top Level) and ccTLD (Country Code Top Level Domain). Historically a gTLD was meant to
tell the user the domain name's purpose; for example, a .com would be for
commercial purposes, .org for an organisation, .edu for education and .gov for government. And a ccTLD was
used for geographical purposes, for example, .ca for sites based in Canada,
.co.uk for sites based in the United Kingdom and so on. Due to such demand,
there is an influx of new gTLDs ranging from .online , .club , .website , .biz
and so many more. For a full list of over 2000 TLDs click here.
Also Read
: How website works
Brought to you by Hacking Truth
Second-Level Domain
Taking google.com as an example, the .com part is the TLD,
and google is the Second Level Domain. When registering a domain name, the
second-level domain is limited to 63 characters + the TLD and can only use a-z
0-9 and hyphens (cannot start or end with hyphens or have consecutive
hyphens).
Subdomain
A
subdomain sits on the left-hand side of the Second-Level Domain
using a period to separate it; for example, in the name admin.google.com the
admin part is the subdomain. A subdomain name has the same creation
restrictions as a Second-Level Domain, being limited to 63 characters and can
only use a-z 0-9 and hyphens (cannot start or end with hyphens or have consecutive hyphens). You can use multiple subdomains split with periods to create longer names,
such as jupiter.servers.google.com. But the maximum length must be kept
below 253 characters. There is no limit to the number of subdomains you
can create for your domain name.
Root Domain "."
TLD .edu .org .gov .com
Second Level Domain mit, hackingtruth, usa, google, nasa, army etc
1) What is the maximum length of a subdomain?
Ans :- 63
2) Which of the following characters cannot be used in a subdomain (
3 b _ - )?
Ans :- _
3) What is the maximum length of a domain name?
Ans :- 253
4) What type of TLD is .co.uk?
Ans :- ccTLD
Record Types
DNS Record Types
DNS isn't just for websites
though, and multiple types of DNS record exist. We'll go over some of the most
common ones that you're likely to come across.
A Record
These records resolve to IPv4 addresses, for example
104.26.10.229
AAAA Record
These
records resolve to IPv6 addresses, for example 2606:4700:20::681a:be5
CNAME Record
These records resolve to another domain name, for example,
google's online shop has the subdomain name store.google.com which returns a
CNAME record shops.shopify.com. Another DNS request would then be made to
shops.shopify.com to work out the IP address.
MX Record
These records resolve to the address of the servers that handle
the email for the domain you are querying, for example an MX record response
for google.com would look something like alt1.aspmx.l.google.com. These
records also come with a priority flag. This tells the client in which order
to try the servers, this is perfect for if the main server goes down and email
needs to be sent to a backup server.
TXT Record
TXT records are free text fields where any text-based data can be
stored. TXT records have multiple uses, but some common ones can be to list
servers that have the authority to send an email on behalf of the domain (this
can help in the battle against spam and spoofed email). They can also be used
to verify ownership of the domain name when signing up for third party
services.
What type of record would be used to advise where to send
email?
1) What type of record would be used to advise where to send email?
Ans :- MX
2) What type of record handles IPv6 addresses?
Ans :- AAAA
Making A Request
What happens when you make a DNS request
1) When you request a domain name, your computer first checks its local cache to
see if you've previously looked up the address recently; if not, a request to
your Recursive DNS Server will be made.
2) A
Recursive DNS Server is usually provided by your ISP, but you
can also choose your own. This server also has a local cache of recently
looked up domain names. If a result is found locally, this is sent back to
your computer, and your request ends here (this is common for popular and
heavily requested services such as Google, Facebook, Twitter). If the request
cannot be found locally, a journey begins to find the correct answer, starting
with the internet's root DNS servers.
3) The root servers act as the DNS backbone of the
internet; their job is to redirect you to the correct Top Level Domain Server,
depending on your request. If, for example, you request www.google.com, the
root server will recognise the Top Level Domain of .com and refer you to the
correct TLD server that deals with .com addresses.
4) The TLD server holds records for where to find the
authoritative server to answer the DNS request. The authoritative server is
often also known as the nameserver for the domain. For example, the name
server for google.com is kip.ns.cloudflare.com and
uma.ns.cloudflare.com. You'll often find multiple nameservers for a
domain name to act as a backup in case one goes down.
5) An authoritative DNS server is the server that is responsible for storing the DNS records for a
particular domain name and where any updates to your domain name DNS records
would be made. Depending on the record type, the DNS record is then sent back
to the Recursive DNS Server, where a local copy will be cached for future
requests and then relayed back to the original client that made the request.
DNS records all come with a TTL (Time To Live) value. This value is a number
represented in seconds that the response should be saved for locally until you
have to look it up again. Caching saves on having to make a DNS request every
time you communicate with a server.
1) What field specifies how long a DNS record should be cached for?
Ans :- TTL
2) What type of DNS Server is usually provided by your ISP?
Ans :- recursive
3) What type of server holds all the records for a domain?
Ans :- authoritative
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