Transport and Application Layer | Quiz with Answers

1.  If a TCP socket is ready and listening for incoming connections, it's in the ______ state. 
  ESTABLISHED
  CLOSE_WAIT
  SYN_SENT
  LISTEN 

           Answer - LISTEN

Explanation - The LISTEN state means that a port is waiting for something to connect to it. 

  
2.  The most common example of a connection-oriented protocol is _____
  UDP
  TCP
  IP 

Answer - TCP

Explanation - Other examples of connection-oriented protocols exist, but TCP is, by far, the most common. 

3.  The sequence of SYN, SYN/ACK, and ACK packets is known as the _________.

three-way handshake 
four-way handshake
two-way handshake
high five  

Answer - three-way handshake

Explanation - That series of flags is used to establish every TCP connection.




4.  Ports that are generally used to establish outbound connections are known as ______ ports.
  system
  reserved
  ephemeral
  registered 

Answer - ephemeral

 Explanation - The exact ports used are different, depending on the operating system, but they're all known as ephemeral ports.

 5.  How many bits are used to direct traffic to specific services running on a networked computer?
  16
  32
  8
  12 

 Answer - 16

 Explanation - A port is a 16-bit number that's used to direct traffic to specific services running on a networked computer.


6.  A network has the ability to direct traffic toward all of the receiving services. What provides this ability in the transport layer?
  File Transfer
  Multiplexing
  Socket address
  Demultiplexing 

Answer -  Multiplexing

 Explanation - Multiplexing in the transport layer means that nodes on a network have the ability to direct traffic toward many different receiving services.


7.  A connection has been terminated and no communication is possible. What is the Transmission Control Protocol (TCP) socket state?
  FINISHED
  CLOSE_WAIT
  FIN_WAIT
  CLOSED 

 Answer - CLOSED

 Explanation - The TCP socket will be in the CLOSED state when the connection has been fully terminated and no further communication is possible.


8.  Which field in a Transmission Control Protocol (TCP) header is chosen from ephemeral ports?
  Sequence number
  Source port
  Destination port
  Acknowledgement number

Answer -  Source port

Explanation - A source port is a high-numbered port chosen from a special section of ports known as ephemeral ports.


9. How many bits are reserved for the Transmission Control Protocol (TCP) flags?
  10
  8
  6
  4 

Answer - 6

Explanation - 6 bits are reserved for the 6 TCP control flags.


10. A connection, at which layer, implies that every segment of data sent is acknowledged?
  Data link
  Network
  Transport
  Application 

Answer -  Transport

Explanation - A connection at the transport layer implies that every segment of data sent is acknowledged.

11. Connection-oriented protocols protect against dropped data by forming connections and using what type of constant stream?
  Acknowledgements
  Verifiers
  Approvals
  Checks  

 Answer - Acknowledgements

 Explanation - Connection-oriented protocols protect against dropped data with a constant stream of acknowledgements.

12. How many Transmission Control Protocol (TCP) control flags are there?
  6
  5
  7
  8

  Answer - 6

 Explanation - There are 6 TCP control flags. 

 13. One side in a Transmission Control Protocol (TCP) connection has not been able to properly recover from a series of malformed segments. Which Transmission Control Protocol (TCP) flag will be used?
  PSH
  FIN
  SYN
  RST 

 Answer - RST

 Explanation - The RST flag is short for reset. This flag will start the communication from scratch, if one side cannot recover from a series of missing or malformed segments.

14.Which Transmission Control Protocol (TCP) flag is used to make sure the receiving end knows how to examine the sequence number field?
  ACK
  SYN
  PSH
  URG

  Answer - SYN

  Explanation -Answer - The SYN flag is used to make sure the receiving end knows how to examine the sequence number field.

Steps of Name Resolution in DNS

 Hello,    

Today we are going to discuss 

Steps of Name Resolution in DNS

      DNS is a system that converts domain names into IP addresses. It's the way humans are likely to remember and categorize things resolved into the way computers prefer to think of things. This process of using DNS to turn a domain name into an IP address is known as name resolution. The first thing that's important to know is that DNS servers, are one of the things that need to be specifically configured at a node on a network. 

     There are five primary types of DNS servers:

•  caching name servers
•  recursive name servers
•  root name servers
•  TLD name servers
•  authoritative name servers. 

      It's important to note that any given DNS server can fulfill many of these roles at once. Caching and recursive name servers are generally provided by an ISP or your local network. Their purpose is to store domain name lookups for a certain amount of time. As you'll see in a moment, there are lots of steps in order to perform a fully qualified resolution of a domain name. In order to prevent this from happening every single time a new TCP connection is established, your ISP or local network will generally have a caching name server available. 

     Most caching name servers are also recursive name servers. Recursive name servers are ones that perform full DNS resolution requests. In most cases, your local name server will perform the duties of both, but it's definitely possible for a name server to be either just caching or just recursive. 

     Let's look at what happens when your local recursive server needs to perform a full recursive resolution. The first step is always to contact a root named server, there are 13 total root name servers and they're responsible for directing queries toward the appropriate TLD name server. In the past, these 13 root servers were distributed to very specific geographic regions, but today, they're mostly distributed across the globe via anycast. Anycast is a technique that's used to route traffic to different destinations depending on factors like location, congestion, or link health. Using anycast, a computer can send a data gram to a specific IP but could see it routed to one of many different actual destinations depending on a few factors. 

      The root servers will respond to a DNS lookup with the TLD name server that should be queried. TLD stands for top level domain and represents the top of the hierarchical DNS name resolution system. A TLD is the last part of any domain name, using www.facebook.com as an example again, the dot com portion should be thought of as the TLD. For each TLD in existence, there is a TLD name server, but just like with root servers, this doesn't mean there's only physically one server in question, it's most likely a global distribution of any cast accessible servers responsible for each TLD. The TLD name servers will respond again with a redirect, this time informing the computer performing the name lookup with what authoritative name server to contact. Authoritative name servers are responsible for the last two parts of any domain name which is the resolution at which a single organization may be responsible for DNS lookups.  

     Your computer will blindly send traffic to whatever IP it's told to. So by using a hierarchical system controlled by trusted entities in the way DNS does, we can better ensure that the responses to DNS lookups are accurate.

 

Why do we need DNS?

Hello Guys,

Today we are going to discuss 

why we need DNS?

     Computers speak to each other in numbers. At the very lowest levels, all computers really understand are 1 and 0. Reading binary numbers isn't the easiest for humans, so most binary numbers are represented in lots of different forms. This is especially true in the realm of networking. Remember that an IP address is really just a 32-bit binary number, but it's normally written out as 4 octets in decimal form since that's easier for humans to read. You might also remember that MAC addresses are just 48-bit binary numbers that are normally written out in 6 groupings of 2 hexadecimal digits each. While remembering 192.168.1.100 might be easier than remembering a long string of 1s and 0s, It still doesn't do a very good job when you have to remember more than just a few addresses. Imagine having to remember the four octets of an IP address for

every website you visit. It's just not a thing that the human brain is normally good at. 

 

     Humans are much better at remembering words. That's where DNS, or domain name system, comes into play. DNS is a global and highly distributed network service that resolves strings of letters into IP address for you. Let's say you wanted to check a weather website to see what the temperature is going to be like. It's much easier to type www.weather.com into a web browser than it is to remember that one of the IP adresses for this site is 184.29.131.121. The IP address for a domain name can also change all the time for a lot of different reasons. A domain name is just the term we use for something that can be resolved by DNS. In the example we just used, www.weather.com would be the domain name, and the IP it resolves to could change, depending on a variety of factors. Let's say that weather.com was moving their web server to a new data center. 

     So, not only does DNS make it easier for humans to remember how to get to a website, It also lets administrative changes happen behind the scenes without an end user having to change their behavior. Try to imagine a world where you'd have to remember every IP for every website you visit, while also having to memorize new ones if something changed. We'd spend our whole day memorizing numbers. The importance of DNS for how the Internet operates, today, can't be overstated.