HTTP/2 or HTTP Version 2 is the second major version
of HTTP network protocol. It is based on SPDY/2 to improve web
performance to a very great extent. HTTP/2 is developed by the Hypertext
Transfer Protocol working group of the Internet Engineering Task Force.
HTTP
1.1 was a major move from HTTP 1.0 as it allowed persisted
connections(more than one request/response on the same HTTP connection),
improved caching, new status code, Enhanced compression support, OPTION
method for Cross Origin Resource Sharing in web application and much
more.
HTTP/1.1 has served the Web well for more than fifteen
years, but its age is starting to show. Loading a Web page is more
resource intensive than ever, and loading all of those assets
efficiently is difficult, because HTTP practically only allows one
outstanding request per TCP connection.
Because of which, many TCP connections are created to
issue parallel requests. And since there isn’t any limit on this; too
many connections are used most of the times which leads to TCP
congestion and unfair resource usage by browsers. It also means lots of
duplicate data being transferred “on the wire”.
If too many requests are made, it hurts performance.
This has led the industry to a place where it’s considered Best Practice
to do things like spriting, data: inlining, domain sharding and
concatenation. These hacks are indications of underlying problems in the
protocol itself, and cause a number of problems on their own when used.
HTTP/2, on the other hand, enables a more efficient use of
network resources and a reduced perception of latency by introducing
header field compression and allowing multiple concurrent exchanges on
the same connection. It also introduces unsolicited push of
representations from servers to clients. This specification is an
alternative to, but does not obsolete, the HTTP/1.1 message syntax.
HTTP’s existing semantics remains unchanged.
At a high level, HTTP/2:
is binary, instead of textual
is fully multiplexed, instead of ordered and blocking
can therefore, use one connection for parallelism
uses header compression to reduce overhead
allows servers to “push” responses proactively into client caches
DNS stands for Domain Name System is used to as the
medium to translate domain names to their respective IP addresses when a
client initiates a request query. DNS stores the database of all the
domain names and their IP addresses which are registered on the network.
Most
of us are quite familiar with the term DNS or Domain Name System. DNS
can be thought of as an attendance register for various websites present
over the internet. In the case of DNS, it maintains the database of all
the websites Domain Names and their IP (Internet Protocol) addresses
that are operational all over the world.
Historical Notes
The origins of DNS date back to the time of ARPANET, when there were only a few computers to get an entry in the database. A HOSTS.TXT
file was maintained by Stanford Research Institute, which constituted
the data of all the machines, and was copied by all the host machines to
remain updated.
Jon Postel from the Information Sciences Institute requested Paul
Mockapetris to design the very first implementation of DNS, at the
University of California, Irvine, in 1983. Then in 1984, BIND (Berkeley
Internet Name Domain) was created by four students, Douglas Terry, Mark
Painter, David Riggle, Songnian Zhou, for Unix machines. After some
revisions made in 1985 by Kevin Dunlap, it was later ported to Windows
machines, and is still the most widely used DNS on the planet.
Working Mechanism
To understand the basic working of DNS, let me guide you with an
example of a hotel. Let us assume, you need to visit your friend at some
hotel. Now, what will you do? You’ll reach the hotel reception and ask
the receptionist for room number of your friend. In order to do so,
you’ll need to tell the name of your friend to the receptionist, who’ll
check the same in her database and satisfy you with the room number of
your friend. She’ll also call your friend to confirm whether he is
available or not.
Now, try to relate the example to working of DNS. In this case,
you’re the client sending a request to a DNS server, the receptionist,
and your friend’s name is the domain name and his room number is his IP
address.
The receptionist will type your friend’s name in her computer
containing the database of all the guests, called the Domain Name Space,
if your friend is staying in the hotel she’ll tell you the room number,
otherwise not. Similar thing happens, when you type the website name in
your browser, the browser sends a request to the DNS server, if the
website domain name is registered in the database with the DNS, then
it’ll reply you with the IP address of the website you are trying to
access, which is something like 117.234.214.14
Understanding the Domain Name and IP Address
Take the domain name, http://www.google.com.
The naming convention moves from right to left and vice-versa for IP
address. In the domain name for Google, first the DNS will check for com which stands for commercial domain, and is a top-level domain. Proceeding further, google.com, is a sub-domain to com and subsequently www,
is a sub-domain to com domain. The dot (.) is used to separate the
domains from their sub-domains. The full domain name can only consist of
253 characters.
Now, if some wants to know the domain name registered against an IP
address, he will request the DNS server with the IP address of the
website. Say, the IP address sent is 31.13.79.246, the DNS will first
check the 31 then 13 then 79 and finally 246, concluding that the IP
address belongs to http://www.fb.com.
The DNS resembles the hierarchy structure of a tree, not the biological
one, there is a different tree in computer data structures, in which
the address 31 belongs to the top position of the tree and is the
primary domain in the hierarchy, addresses 13, 79, 246 are consecutive
sub-domains. The number 246 refers to the server machine hosting the
website http://www.fb.com.
All this domain and sub-domain thing is not that much complicated as
you think, but it’ll take some time for you to get it correctly if
you’re new to this concept.
Evolution of DNS
In earlier days, a master file was maintained by one main server
which was updated manually with the entry of every new website and then
it was copied by other servers. But, as the count of websites
proliferated with time, it was hard to maintain the domain name database
manually. So, the need of an automated system was felt and then the
ability to automatically update the database all around the world was
introduced in the newer generations of DNS.
So, if you register your website name with a Domain Name Registrar,
it will take around 24 hours for your website to be present in the DNS
databases all around the world.
The Master-Slave server relations were introduced in which a master
server maintained the database and Slave server only had to copy the
database to remain updated. In order to facilitate the dynamic updates
to DNS database, the mechanisms NOTIFY and IXFR were introduced.
In NOTIFY, when the master server updates the database, it sends a
notification to the slave servers about the update, which then copies
the database. IXFR (Incremental Zone Transfer) eliminates the need to
copy the whole database every time a single entry has been made, it
allows the slave servers to only add the updated entry in their
database, thus reducing the efforts and making the dynamic update
process faster.
Resolving IP Address
It refers to the process of translation of a domain name to its
respective IP address. The DNS resolver is the client PC, you in that
hotel example, which sends the query to the DNS server, the
receptionist. There are two methods used for resolution: Recursive: Now continuing with the hotel example,
assume the hotel has more than one branch in the city, and the
receptionist was unable to find your friend’s room number. Then she’ll
check if your friend has been staying in the other branch by contacting
the receptionist present there. So, if the DNS server in unable to find
any IP associated to the domain name sent in the query then it’ll ask
the other servers connected to resolve the IP address for the requested
domain. It’ll gather the information from those servers and reply to you
with the appropriate IP address. Iterative: Suppose you also want to know the floor
on which the friend’s room is situated, in order to do so, you’ll again
ask the receptionist. Similarly, if the DNS resolver wants more
information about a domain, it’ll initiate a new query for the same DNS
server.
DNS Cache
The DNS server temporarily stores the request queries in the form of
Cache, so as to reduce the response time if any other DNS resolver
requests the same query. The time for which the Cache information
remains valid is called TTL (Time To Live), is set by the administrator
for each query record stored in the cache.
DNS Applications
The first and foremost application of DNS is nslookup, in which a DNS
server replies with the IP address of the domain name requested in the
query. DNS is used by different Mail Transfer Agents (MTA) like
Microsoft Exchange Server and IBM Domino, so that they can deliver the
e-mails more efficiently.
DNS proves to be very helpful in identifying black-listed IP
addresses over the internet and barring the users from accessing them.
This helps in protecting the users from spam e-mails and potential
hacking attacks.
The data for each domain name and its IP address is kept on more than
one DNS server, so as to retrieve the data in case any problem occurs
on one server.
DNS Vulnerabilities
Cache Poisoning: Also called DNS Spoofing, is the
technique used by malevolent people, in which they alter the data in
resolver cache of the DNS server, rendering incorrect IP address to DNS
resolver, may be to divert the user to a hacker’s machine.
DNS responses are not encrypted thus allowing the possibilities of
potential attacks. However, Domain Name System Security Extensions
(DNSSEC) are used to render cryptographically signed DNS responses. Phishing attacks can be planned due to visual
resemblance of some characters on the user’s screen, like the letter l
and 1 appear the same on some screens, thus redirecting users to
different IP addresses by displaying the same look and feel as of the
original website.
Use custom DNS
What if the that hotel receptionist is very slow and many people are
asking for room numbers at same time, then she’ll not be able to provide
you with correct room number quickly. So, you may ask some other person
at the reception counter to attend your concern. Similarly, when we
connect to the internet, we generally use the DNS Server provided by our
ISPs. But what if the default DNS server is irresponsive or if it can’t
handle a large number of queries at a given moment, such instances will
only degrade your browsing experience. But don’t worry, there is
another way out. You can configure your system to use a different DNS
server for resolving IP addresses.
Popular DNS servers:
Google’s Public DNS: The search giant has set-up
some serious high-grade DNS servers capable of handling millions of
requests at any given moment. And they’re absolutely free to use like
Google’s other services. You can configure your machine to use the
following DNS addresses: 8.8.8.8 and 8.8.4.4 OpenDNS: This is a private company which provides
safe and reliable DNS server for free. Just configure the following
addresses on your machine: 208.67.222.222 and 208.67.220.220
For those readers who don’t know how to configure DNS on your machine, please refer the link below:
Winding Up
DNS has been a topic of utmost importance since its advent as a
systematic way to maintain such a huge database of millions of websites
and servers around the world. Without DNS, it would’ve instigated a
whole lot of mess of all the domain names and IP addresses, and it
would’ve taken ages just to locate google.com
from a haphazard collection of all the domain names. DNS has
streamlined the process of IP resolution and seriously, if DNS wasn’t
there, I know you would’ve burnt your brain circuits in order to
remember all those IP addresses. And let me ask you, do you remember
Facebook’s IP address I mentioned above. And don’t scroll up now, even I
don’t remember it, because DNS is there to remember it for us. We only
need to express our gratitude for the noble work DNS has been doing
since the last three decades, and it has become faster, smarter and more
reliable.
Watch this video about DNS:
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