CN Important Questions 3rd Internals

Whats is Tunneling?

Tunneling, also known as "port forwarding," is the transmission of data intended for use only within a private, usually corporate network through a public network in such a way that the routing nodes in the public network are unaware that the transmission is part of a private network. Tunneling is generally done by encapsulating the private network data and protocol information within the public network transmission units so that the private network protocol information appears to the public network as data. Tunneling allows the use of the Internet, which is a public network, to convey data on behalf of a private network.

There are various protocols that allow tunneling to occur, including:

  • Point-to-Point Tunneling Protocol (PPTP): PPTP keeps proprietary data secure even when it is being communicated over public networks. Authorized users can access a private network called a virtual private network, which is provided by an Internet service provider. This is a private network in the “virtual” sense because it is actually being created in a tunneled environment.
  • Layer Two Tunneling Protocol (L2TP): This type of tunneling protocol involves a combination of using PPTP and Layer 2 Forwarding.

Tunneling is a way for communication to be conducted over a private network but tunneled through a public network. This is particularly useful in a corporate setting and also offers security features such as encryption options.

2) IPV4 to IPV6 Conversion ?

An IPv4 address : example
  • Each Octet (8 bits) “between the dot-thingys” denote 1 byte
An IPv6 address : example 2001:0db8:85a3:0000:0000:8a2e:0370:7334
  • Two Tuples (1 Tuple = 4 bits = 1 Hex character) denotes 1 byte
Then converting is easy. Lets take the following IPv4 address : and convert it to Hex.
Step1 >
Divide the first octet (192) by 16 (since Hex is a Base-16)
IE : 192/16 = 12 times exactly with 0 left over
– 12 in Hex is represented as C
– 0 (zero) in Hex is, you guessed it, 0
Thus 192 in HEX is C0
Step2 >
Repeat step 1 with the second octet (168),
IE : 168/16 = 10 times with 8 left over because 10*6 = 160,
– 10 in HEX is A
– 8 in HEX is 8
Thus 168 in HEX is A8
Step3 >
Repetition rules!!! Third octet (99)
IE : 99/16 = 6 times with 3 left over
– 6 in HEX is 6
– 3 in HEX is 3
Thus 99 in HEX is 63
Step4 >
Last octet
IE : 1/16 = 0 times with 1 left over
– 0 in HEX is, yeah it is 0
– 1 in HEX is 1
Thus 1 in HEX is 01

3) what is Handshaking?

The process by which two devices initiate communications. Handshaking begins when one device sends a message to another device indicating that it wants to establish a communications channel. The two devices then send several messages back and forth that enable them to agree on a communications protocol.  

In telephone communication, handshaking is the exchange of information between two modems and the resulting agreement about which protocol to use that precedes each telephone connection. You can hear the handshaking in those crunching and other sounds when you make a dial-out call from your computer

Since the modems at each end of the line may have different capabilities, they need to inform each other and settle on the highest transmission speed they can both use. At higher speeds, the modems have to determine the length of line delays so that echo cancellers can be used properly.
 4) Resource Allocation Schema ? 
(will be back with answer for this )

5) Priority Queue ?

n computer science, a priority queue is an abstract data type which is like a regular queue or stack data structure, but where additionally each element has a "priority" associated with it. In a priority queue, an element with high priority is served before an element with low priority. If two elements have the same priority, they are served according to their order in the queue.
While priority queues are often implemented with heaps, they are conceptually distinct from heaps. A priority queue is an abstract concept like "a list" or "a map"; just as a list can be implemented with a linked list or an array, a priority queue can be implemented with a heap or a variety of other methods such as an unordered array.

A sorting algorithm can also be used to implement a priority queue.
We present a general deterministic linear space reduction from priority queues to sorting implying that if we can sort up to n keys in S(n) time per key, then there is a priority queue supporting delete and insert in O(S(n)) time and find-min in constant time.
6)  Explain ICMP in detail ?

ICMP (Internet Control Message Protocol) is located at the Network layer of the OSI model (or just above it in the Internet layer, as some argue), and is an integral part of the Internet Protocol suite ( commonly referred to as TCP/IP). ICMP is assigned Protocol Number 1 in the IP suite according to Designed to act as an error reporting and query service, it plays a crucial role in the host-to-host datagram service in network communication. It is the part of the IP service that acts as the feedback system in network IP communication, making sure that undeliverable packets are reported to the sending host, such as the router or the gateway. Any IP network device can send ICMP datagrams.

One of the most well-known and useful messages in an ICMP datagram is the Destination Unreachable message. Destination Unreachable messages are generated for several reasons, including unable to reach a network, a host, a port, or a protocol. A router sends these Destination Unreachable messages back to the host, which then usually sends it to the application that generated the original packet. 

ICMP messages are datagrams encapsulated within IP packets, and is used by both IPv4 (ICMPv4) and IPv6 (ICMPv6) protocols.These packets start with an IP header, followed by the ICMP header, type and code, checksum, and data. The data depends on the type and code fields, which identify the ICMP message being sent.
One of the most important parts of the Internet Protocol suite, ICMP serves a crucial role in IP network communication. It ensures that a transmitting host knows if its packets are not being received by the remote host, providing crucial information regarding network problems as well as helping hosts transmit data more efficiently.
 7) Explain in detail TCP packet Format  ?

The Transmission Control Protocol (TCP) is a core protocol of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonly referred to as TCP/IP. TCP provides reliable, ordered, and error-checked delivery of a stream of octets between applications running on hosts communicating over an IP network.
(Source Wiki)


 7) IPV4 and IPV6 Packet Format ?

  • Version - Protocol version identification. It helps to identify protocol version as IPv6.
  • Traffic Class - Intended for the Quality of Service (QoS). It may distinguish various classes or priorities of traffic (in combination with other header fields, e.g. source/destination addresses).
  • Flow Label - Identifies a flow which is a “group of related datagrams or flow from same session”.
  • Payload Length – The Total Length is the length of the IPv4 packet including the header.But in IPv6, the Payload Length does not include the 40-byte IPv6 header. It save the host or router receiving a packet from having check whether the packet is large enough to hold the IP header in initial phase. Making for a small efficiency gain. Despite the name, the Payload Length field includes the length of any additional headers, not just the length of the user data.It is in Bytes, so the maximum possible payload size is 64 KB.
  • Next Header -The protocol header which follows, It identifies the type of following data - it may be some extension header or upper layer protocol (TCP, UDP) data.
  • Hop Limit - Time to Live (TTL) is now called Hop Limit in IPv6. The sending node assigns some value to this field defining the reach of given datagram. Every forwarding host decreases the value by 1. If decremented to zero, the datagram is dropped and an ICMP message is sent to the sender. It protects the IPv6 transport system against routing loops - in the case of such loop the datagram circulates around the loop for a limited time only.
  • Source Address - It contains the IPv6 address of the host who sent this datagram.
  • Destination Address - This is the target/destination address  where  the datagram should be delivered to particular IPv6 address.

    Compulsary Question ;

  • what are the applications of UDP  ?

    Some of the real time applications of UDP are  as follows .

    Media Streaming, If you are watching a movie?would you
    prefer that your movie comes..perfectly?.but u need to wait
    a long time before you see the next frame ?..or would you
    prefer the movie to keep streaming?Yes?The second option is
    definely better?.This is what we need UDP 

      2) UDP:- Postcard communication

      3) VOIP :Voip runs on UDP because the tcp check for the
acknowledgement of data transmitted. So if Voip runs on tcp
the voice data would be perfectly received but the flow of
voice would be improper.

As the Voip runs on UDP the voice, sometimes we get
disturbance in voice and also we are get getting bad quality
of sound. It is because of lost of packets in network as UDP
do not acknowledge the data on transmission. 

4) ==UDP ( User Datagram Protocol )
* Transport Layered
* Suit Protocol
* No Acknowledgment
* No Error Detection and Correction
* No relaiblity
* Fast
* Connectionless
* 1 – 65,535 logical Ports
* 1 – 1024 well reserved ports
* 90% of Voice Communcation uses the UDP

5)If TCP is so good why is UDP still in use?

TCP and UDP are both same level protocol, if add session management , ensure data delivery , and transmission control to UDP eventually u will get TCP :),

UDP has it own reasons for existence, first and foremost, it has low header overheas, just 4 bytes header, fast data delivery, at the cost of reliablity etc/ etc.hence it is mostly used in scenarios where speed is of concern , like broadcasting , routing table inforamtion exchange, multimedia streaming, where timely delivery is more important then delayed data.

tcp on the other hand ensures data delivery but at the cost of speed and bandwidth. it adds its own session managment and data windows(how much data can be recived by the reciever) inforamation to the packets. usually the packets get framgmented and reaches in arbitrary order at the destination ,which then assembles them and present to the reciver and also acknowledge the sender.
so each has its own pros and cons 


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