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$\textsf{HELO}$ and $\textsf{PORT}$, respectively, are commands from the protocols:

  1. $\textsf{FTP}$ and $\textsf{HTTP}$
  2. $\textsf{TELNET}$ and $\textsf{POP3}$
  3. $\textsf{HTTP}$ and $\textsf{TELNET}$
  4. $\textsf{SMTP}$ and $\textsf{FTP}$
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HELO - Sender's Host Name (SMTP)
PORT -  is a ftp command.
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Option D) SMTP and FTP
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5 Answers

26 votes
26 votes
41 votes
41 votes

For SMTP: Various commands

  1. HELO : It's the first SMTP command: is starts the conversation identifying the sender server and is generally followed by its domain name.
  2. EHLO : An alternative command to start the conversation, underlying that the server is using the Extended SMTP protocol.
  3. MAIL FROM : With this SMTP command the operations begin: the sender states the source email address in the "From" field and actually starts the email transfer.
  4. RCPT TO : It identifies the recipient of the email; if there are more than one, the command is simply repeated address by address.
  5. SIZE : This SMTP command informs the remote server about the estimated size (in terms of bytes) of the attached email. It can also be used to report the maximum size of a message to be accepted by the server.
  6. DATA : With the DATA command the email content begins to be transferred; it's generally followed by a 354 reply code given by the server, giving the permission to start the actual transmission.
  7. VRFY : The server is asked to verify whether a particular email address or username actually exists.
  8. TURN: This command is used to invert roles between the client and the server, without the need to run a new connaction.
  9. AUTH : With the AUTH command, the client authenticates itself to the server, giving its username and password. It's another layer of security to guarantee a proper transmission.
  10. RSET : It communicates the server that the ongoing email transmission is going to be terminated, though the SMTP conversation won't be closed (like in the case of QUIT).
  11. EXPN : This SMTP command asks for a confirmation about the identification of a mailing list.
  12. HELP : It's a client's request for some information that can be useful for the a successful transfer of the email.
  13. QUIT : It terminates the SMTP conversation.

FTP may run in active or passive mode, which determines how the data connection is established. In both cases, the client creates a TCP control connection from a random, usually an unprivileged, port N to the FTP server command port 21.

For HTTP commands :

  1. GET :Retrieves the document specified in the URL property (use GetHeader to retrieve header information and GetChunk to get the rest of the information)
  2. HEAD: Gets the header information (use Get Header to retrieve header information).
  3. POST : Sends data to the server.
  4. PUT : Replaces the page specified in the URL property with the specified data

D is answer

4 Comments

Where did u get this ?? resources ??
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From book Forouzan .
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FTP has port number 21 too
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srestha

yes port no 20 for data connection.

and port no 21 for control connection.

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29 votes
29 votes

answer is D

HELO:  The domain name or IP address of the SMTP client is usually sent as an argument together with the command (e.g. “HELO client.example.com”). If a domain name is used as an argument with the HELO command, it must be a fully qualified domain name (also called FQDN).

FTP  : FTP may run in active or passive mode, which determines how the data connection is established. In both cases, the client creates a TCP control connection from a random, usually an unprivileged, port N to the FTP server command port 21.

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3 Comments

NO. in both the cases it doesnt use port 21 on server side: here’s the reference: 

In situations where the client is behind a firewall and unable to accept incoming TCP connections, passive mode may be used. In this mode, the client uses the control connection to send a PASV command to the server and then receives a server IP address and server port number from the server,[9] which the client then uses to open a data connection from an arbitrary client port to the server IP address and server port number received.

from:http://en.wikipedia.org/wiki/File_Transfer_Protocol#Protocol_overview

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@KartikGawande , read the concept once again please...

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 i have been trying to understand where i am wrong (if i am) but i dont see what u trying to tell me here. As is given in my above comment the client clearly is going to use the port no given by the server(as a response to the PASV command) for connection establishment if its in passive mode. Can u tell me where u think i am wrong? it will be very helpful

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1 vote
1 vote
Option-D

HELO(HELLO) and Port is usualy command of SMTP as well as FTP.

For more information please read the book of Top down approach of computer network.
Answer:

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