Which of the following TCP IP application layer protocols is used for email transmissions FTP https SMTP IP?

Following questions have been asked in GATE CS 2012 exam. 

1) The protocol data unit(PDU) for the application layer in the Internet stack is 
(A) Segment 
(B) Datagram 
(C) Message 
(D) Frame 

Answer (C) 
The Protocol Data Unit for the Application layer in the Internet Stack (or TCP/IP) is called Message. 

2) Which of the following transport layer protocols is used to support electronic mail? 
(A) SMTP 
(B) IP 
(C) TCP 
(D) UDP 

Answer (C) 
E-mail uses SMTP as application layer protocol. SMTP uses TCP as transport layer protocol. 

3) In the IPv4 addressing format, the number of networks allowed under Class C addresses is 
(A) 2^14 
(B) 2^7 
(C) 2^21 
(D) 2^24 

Answer (C) 
In class C, 8 bits are reserved for Host Id and 24 bits are reserved for Network Id. Out of these 24 Network Id bits, the leading 3 bits are fixed as 110. So remaining 21 bits can be used for different networks. See this for more details. 

4) An Internet Service Provider(ISP) has the following chunk of CIDR-based IP addresses available with it:245.248.128.0/20. The ISP wants to give half of this chunk of addresses to Organization A, and a quarter to Organization B, while retaining the remaining with itself. Which of the following is a valid allocation of addresses to A and B? 
(A) 245.248.136.0/21 and 245.248.128.0/22 
(B) 245.248.128.0/21 and 245.248.128.0/22 
(C) 245.248.132.0/22 and 245.248.132.0/21 
(D) 245.248.136.0/22 and 245.248.132.0/21 

Answer (A) 
Since routing prefix is 20, the ISP has 2^(32-20) or 2^12 addresses. Out of these 2^12 addresses, half (or 2^11) addresses have to be given to organization A and quarter (2^10) addresses have to be given to organization B. So routing prefix for organization A will be 21. For B, it will be 22. If we see all options given in question, only options (A) and (B) are left as only these options have same number of routing prefixes. Now we need to choose from option (A) and (B). 
To assign addresses to organization A, ISP needs to take first 20 bits from 245.248.128.0 and fix the 21st bit as 0 or 1. Similarly, ISP needs to fix 21st and 22nd bits for organization B. If we take a closer look at the options (A) and (B), we can see the 21st and 22nd bits for organization B are considered as 0 in both options. So 21st bit of organization A must be 1. Now take the first 20 bits from 245.248.128.0 and 21st bit as 1, we get addresses for organization A as 245.248.136.0/21 

Please see GATE Corner for all previous year paper/solutions/explanations, syllabus, important dates, notes, etc. 

Please write comments if you find any of the answers/explanations incorrect, or you want to share more information about the topics discussed above.
 

Application Layer:-

The application layer is present at the top of the OSI model. It is the layer through which users interact. It provides services to the user. 

Application Layer protocol:-

1. TELNET:

Telnet stands for the TELetype NETwork. It helps in terminal emulation. It allows Telnet clients to access the resources of the Telnet server. It is used for managing files on the internet. It is used for the initial setup of devices like switches. The telnet command is a command that uses the Telnet protocol to communicate with a remote device or system. Port number of telnet is 23. 
 

Command  

telnet [\\RemoteServer]
\\RemoteServer   : Specifies the name of the server to which you want to connect

2. FTP:

FTP stands for file transfer protocol. It is the protocol that actually lets us transfer files. It can facilitate this between any two machines using it. But FTP is not just a protocol but it is also a program.FTP promotes sharing of files via remote computers with reliable and efficient data transfer. The Port number for FTP is 20 for data and 21 for control. 

Command 

ftp machinename

3. TFTP:

The Trivial File Transfer Protocol (TFTP) is the stripped-down, stock version of FTP, but it’s the protocol of choice if you know exactly what you want and where to find it. It’s a technology for transferring files between network devices and is a simplified version of FTP. The Port number for TFTP is 69.

Command 

tftp [ options... ] [host [port]] [-c command] 

4. NFS:

It stands for a network file system. It allows remote hosts to mount file systems over a network and interact with those file systems as though they are mounted locally. This enables system administrators to consolidate resources onto centralized servers on the network. The Port number for NFS is 2049.

Command 

service nfs start

5. SMTP:

It stands for Simple Mail Transfer Protocol. It is a part of the TCP/IP protocol. Using a process called “store and forward,” SMTP moves your email on and across networks. It works closely with something called the Mail Transfer Agent (MTA) to send your communication to the right computer and email inbox. The Port number for SMTP is 25. 

Command 

MAIL FROM:<?

6. LPD:

It stands for Line Printer Daemon. It is designed for printer sharing. It is the part that receives and processes the request. A “daemon” is a server or agent. The Port number for LPD is 515. 

Command 

lpd [ -d ] [ -l ] [ -D DebugOutputFile]

7. X window:

It defines a protocol for the writing of graphical user interface–based client/server applications. The idea is to allow a program, called a client, to run on one computer. It is primarily used in networks of interconnected mainframes. Port number for X window starts from 6000 and increases by 1 for each server.

Command  

Run xdm in runlevel 5 

8. SNMP:

It stands for Simple Network Management Protocol. It gathers data by polling the devices on the network from a management station at fixed or random intervals, requiring them to disclose certain information. It is a way that servers can share information about their current state, and also a channel through which an administrate can modify pre-defined values. The Port number of SNMP is 161(TCP) and 162(UDP). 
 

Command  

snmpget -mALL -v1 -cpublic snmp_agent_Ip_address sysName.0

9. DNS:

It stands for Domain Name System. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.abc.com might translate to 198.105.232.4. 
The Port number for DNS is 53. 
 

Command  

ipconfig /flushdns

10. DHCP:

It stands for Dynamic Host Configuration Protocol (DHCP). It gives IP addresses to hosts. There is a lot of information a DHCP server can provide to a host when the host is registering for an IP address with the DHCP server. Port number for DHCP is 67, 68. 

Command 

clear ip dhcp binding {address | * }

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Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 

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