3.1 File Transfer Tools and FTP Basics
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Questions and Answers

Which FTP command is used to change the working directory on the remote server?

  • DELE
  • PWD
  • RETR
  • CWD (correct)

    • In passive mode, the server uses which port for data transfer?

  • Any random port >1024 (correct)
  • Port 22
  • Port 21
  • Port 20

    • What is the purpose of the FTP command STOR?

  • Retrieve a file from the remote server
  • List the files in a remote directory
  • Store a file on the remote host (correct)
  • Change the working directory

    • Which FTP command would you use to abort a file transfer?

    <p>ABOR (B)</p> Signup and view all the answers

    Which of the following commands is NOT used for file transfer operations?

    <p>LIST (A)</p> Signup and view all the answers

    What does the FTP command RETR accomplish?

    <p>Retrieve a remote file (B)</p> Signup and view all the answers

    Which command is used to terminate the FTP connection?

    <p>QUIT (A)</p> Signup and view all the answers

    What does the command SIZE return?

    <p>Size of a file (A)</p> Signup and view all the answers

    What occurs when a duplicate datagram is received by either side in TFTP?

    <p>A duplicate acknowledgment is generated. (A), Only the first acknowledgment is considered. (C)</p> Signup and view all the answers

    What is the main issue known as Sorcerer's Apprentice Syndrome (SAS) in TFTP?

    <p>Both sides retransmitting packets on receiving duplicates (A)</p> Signup and view all the answers

    In what scenario would the modification to the TFTP specification become necessary?

    <p>When duplicates of acknowledgments cause retransmission loops (B)</p> Signup and view all the answers

    What modification did the TFTP specification introduce to handle SAS?

    <p>Ignore all duplicated acknowledgments after the first instance (B)</p> Signup and view all the answers

    What is the primary trigger for resending a block in the modified TFTP protocol?

    <p>A timeout occurring (B)</p> Signup and view all the answers

    Which layer of networking can cause loss of Ethernet frames leading to a timeout in TFTP?

    <p>Data link layer (D)</p> Signup and view all the answers

    What is indicated by a timeout event during a TFTP transfer?

    <p>A failure to receive an acknowledgment in time (B)</p> Signup and view all the answers

    What is the maximum size of each data block sent during a file transfer?

    <p>512 bytes (A)</p> Signup and view all the answers

    What must happen before the next data packet can be sent?

    <p>Acknowledge the receipt of the last packet. (D)</p> Signup and view all the answers

    What does a data packet of less than 512 bytes signal during a transfer?

    <p>The transfer has been terminated. (C)</p> Signup and view all the answers

    What strategy ensures that the sender stays synchronized with the receiver?

    <p>Stop-Wait Protocol (A)</p> Signup and view all the answers

    If a packet is lost in the network, what action does the intended recipient take?

    <p>Retransmit its last packet or acknowledgment. (D)</p> Signup and view all the answers

    How many packets does the sender keep for retransmission under the given protocol?

    <p>One packet (B)</p> Signup and view all the answers

    In the protocol discussed, which port is designated for TFTP transfer?

    <p>Port 69 (B)</p> Signup and view all the answers

    What initiates the transfer process in the Trivial File Transfer Protocol?

    <p>A read request from the client. (B)</p> Signup and view all the answers

    What does the Ack Block signify during the TFTP transfer process?

    <p>The server acknowledges receipt of a data block. (A)</p> Signup and view all the answers

    What packet type must the server respond with after sending a data block?

    <p>Acknowledgment packet (A)</p> Signup and view all the answers

    What is the purpose of the first packet sent in a TFTP file transfer?

    <p>It requests a file transfer and specifies file details. (C)</p> Signup and view all the answers

    How is the end of a file indicated in a TFTP transfer?

    <p>By sending a block of less than 512 bytes. (B)</p> Signup and view all the answers

    Which of the following correctly describes a TFTP DATA packet structure?

    <p>2 byte OP Code, 2 bytes, Up to 512 bytes. (C)</p> Signup and view all the answers

    What type of file modes can be specified in a TFTP request?

    <p>Text or Binary (D)</p> Signup and view all the answers

    What triggers the transfer in a TFTP write operation?

    <p>WRQ (Write Request) (B)</p> Signup and view all the answers

    What action is taken if an error message is sent during a TFTP transfer?

    <p>The transfer is terminated. (B)</p> Signup and view all the answers

    Which error code indicates that the requested file was not found?

    <p>ERROR CODE 1 (B)</p> Signup and view all the answers

    In TFTP, which port is typically used by the server to receive write requests?

    <p>Port 69 (A)</p> Signup and view all the answers

    What is the maximum size of a data block in a TFTP transfer?

    <p>512 bytes (D)</p> Signup and view all the answers

    What happens when a data packet is lost during a TFTP file transfer?

    <p>The intended recipient times out and may resend the last packet. (D)</p> Signup and view all the answers

    What occurs after sending Data Block 1 in a TFTP transfer?

    <p>Data Block 2 is sent after receiving Ack Block 1. (C)</p> Signup and view all the answers

    What type of acknowledgement does TFTP use to confirm receipt of a block?

    <p>ACK with block number specified. (C)</p> Signup and view all the answers

    In a TFTP process, what does 'Lost Ack (Timer operation)' refer to?

    <p>The timeout when an acknowledgment of a data block is not received. (B)</p> Signup and view all the answers

    How many bytes make up the OP Code in a TFTP ACK packet?

    <p>2 bytes (C)</p> Signup and view all the answers

    During a TFTP transfer, what is indicated by Ack Block n?

    <p>The completion of the last data block transfer. (C)</p> Signup and view all the answers

    Which operation begins any file transfer in TFTP?

    <p>Request to read or write a file. (A)</p> Signup and view all the answers

    What is the maximum size of each data block sent in TFTP?

    <p>512 Bytes (D)</p> Signup and view all the answers

    What type of request is sent by the client to initiate a read operation in TFTP?

    <p>RRQ (Read Request) (A)</p> Signup and view all the answers

    What action does the server take upon receiving an RRQ?

    <p>It starts sending data blocks starting with Data Block 1. (C)</p> Signup and view all the answers

    What is the role of the timeout in TFTP communication?

    <p>To ensure lost packets are resent in case of no acknowledgment. (C)</p> Signup and view all the answers

    Flashcards

    Active Mode

    A mode where the server connects back to the client on port 20 for data transfer.

    Passive Mode

    A mode where the client connects to a random port on the server for data transfer.

    USER Command

    FTP command to specify the user name during login.

    PASS Command

    FTP command to specify the user's password during login.

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    LIST Command

    FTP command to list files in the current directory.

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    RETR Command

    FTP command to retrieve or download a specified file.

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    STOR Command

    FTP command to upload a specified file to the server.

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    QUIT Command

    FTP command to close the current FTP connection.

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    TFTP

    A protocol for transferring files over a network with simple commands.

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    Read Request Packet

    A packet used to request a file transfer from the server to the client.

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    Write Request Packet

    A packet used to request a file transfer from the client to the server.

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    Data Packet

    Packet containing file data, includes block number and data bytes.

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    Acknowledgement Packet

    Packet sent by the receiver to confirm receipt of a data packet.

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    Error Packet

    Packet sent when there is an error during file transfer.

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    Block Number

    Each block of the file is numbered consecutively starting at 1.

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    End of File Signal

    A block of less than 512 bytes indicates the end of a file transfer.

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    Error Codes

    Standard codes defining specific errors during TFTP operations.

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    TFTP Modes

    Modes specify data transfer format; either Ascii or Binary.

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    Timer operation in TFTP

    How timer functions to ensure reliable data transfer in TFTP.

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    Sorcerer's Apprentice Syndrome (SAS)

    A bug in TFTP causing excessive duplicate transfers due to delayed packets.

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    Why does SAS occur?

    SAS happens when both sides retransmit due to receiving duplicates.

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    How to fix SAS?

    Modify TFTP to ignore duplicate acknowledgments after the first one.

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    Data Block Size in TFTP

    Data blocks in TFTP transfers are typically 512 bytes each.

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    Timeout in TFTP

    A mechanism to resend data if acknowledgment isn't received in time.

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    Data Block

    Chunk of data transferred in TFTP, typically 512 bytes.

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    Ack Block

    Acknowledgment block that confirms receipt of a data block in TFTP.

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    Write Request (WRQ)

    Initiates transfer from client to server in TFTP.

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    Read Request (RRQ)

    Initiates transfer from server to client in TFTP.

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    Lost Packet

    When a data packet fails to reach its destination in TFTP.

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    Timeout

    Period where the recipient waits for an acknowledgment before retrying in TFTP.

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    Resend

    Action taken when a packet is not acknowledged within a time frame.

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    RFC 1350

    The document that defines the TFTP protocol.

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    Port 69

    The port used for TFTP operations like data transfer requests.

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    Fixed Length Blocks

    Data is sent in consistent sizes, here, 512 bytes each.

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    Retransmit

    To send a packet again if the previous one was lost.

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    Error Recovery

    The process of restoring communication after a disruption during data transfer.

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    Stop-and-Wait Protocol

    A method where the sender waits for an acknowledgment before sending the next packet.

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    Trivial File Transfer Protocol (TFTP)

    A simple file transfer protocol designed for transferring files easily.

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    Study Notes

    File Transfer Tools

    • File Transfer Protocol (FTP) is a standard communication protocol used for transferring files over a network.
    • FTP is based on a client-server architecture.
    • FTP uses separate control and data connections.
    • FTP users authenticate using a clear-text sign-in protocol (username and password).
    • FTP allows anonymous connections if configured.
    • Clients include command-line interfaces, graphical user interfaces (GUIs), and web browsers (ftp://).

    Motivation

    • Secure file transfer over the internet is necessary.
    • Some legacy industrial devices only support FTP or TFTP.
    • Secure firewall configuration is crucial.
    • Secure management of remote devices is essential.

    File Transfer Protocol (FTP)

    • Uses TCP at the transport layer.
    • The server listens on port 21.
    • Uses separate control and data channels.
    • The control channel remains open during the session for authentication and directory listing (port 21).
    • The data channel supports file transfers and closes after each transfer (port 20 for Active mode, random port >1024 for Passive mode).
    • Two operational modes: Active and Passive mode.

    Examples of FTP Commands (Authentication)

    • USER - specifies the username for login.
    • PASS - specifies the user's password.

    Examples of FTP Commands (Exploring files)

    • LIST - lists files for a given specification.
    • CWD - changes the current directory.

    Examples of FTP Commands (Downloading/Uplaoding Files)

    • TYPE - sets the file type (ASCII or binary).
    • RETR - retrieves a file.
    • STOR - uploads a file.

    Examples of FTP Commands (Closing the Connection)

    • QUIT - closes the FTP connection.

    Examples of FTP Commands (Additional)

    • ABOR - aborts a file transfer.
    • CWD - changes the working directory.
    • DELE - deletes a remote file.
    • LIST - lists remote files.
    • MDTM - returns the modification time of a file.
    • MKD - makes a remote directory.
    • NLST - names a list of remote directories.
    • PASV - enters passive mode.
    • PORT - opens a data port.
    • PWD - prints the working directory.
    • QUIT - terminates the connection.
    • RETR - retrieves a remote file.
    • RMD - removes a remote directory.
    • RNFR - renames from
    • RNTO - renames to
    • SITE - site-specific commands
    • SIZE - returns the size of a file
    • STOR - stores a file on the remote host
    • TYPE - sets transfer type

    Active Mode (Simplified)

    • Client chooses its port number for the data channel.
    • The server initiates the data channel connection to the client's port.

    Problem with Active Mode

    • Firewalls block incoming connections to the client's port.
    • The incoming port can be in range 1024 - 65,536.
    • Active mode requires firewall setup to allow connections from the server to the client for data transfer.

    Passive Mode

    • Server chooses a port for the data channel and notifies the client.
    • Client initiates the data channel connection to the server's port.

    Trivial File Transfer Protocol (TFTP)

    • RFC 1350.
    • Simple protocol for file transfers within a Local Area Network (LAN).
    • Used for transferring configuration and firmware images to networking devices.
    • Only allows reading or writing a file for a client, without authentication.
    • Uses UDP at the transport layer.
    • Only 5 commands: RRQ (Read Request), WRQ (Write Request), DATA (Data Block), ACK (Acknowledgement), and ERROR.
    • Error control with block numbers and acknowledged data transfer.

    TFTP commands (RFC defines as packets)

    • Read Request (OP Code 1) includes filename and mode (ASCII or binary)
    • Write Request (OP Code 2) includes filename and mode (ASCII or binary)
    • Data packets are numbered consecutively starting at 1, contain up to 512 bytes of data.
    • Each data packet must be acknowledged by the receiver.
    • Error messages (OP Code 5) can be sent.

    Trivial File Transfer Protocol (TFTP) Overview

    • Transfer starts with a request to read or write a file.
    • The server opens a logical connection.
    • Files sent in 512-byte data blocks.
    • Each block acknowledged by receiver before next sent.
    • Transfers terminate with data less than 512 bytes.
    • Receiver may resend if data block lost, due to Time Out.
    • Stop-and-wait protocol used.

    TFTP Commands (Simplified)

    • Requests (RRQ, WRQ)
    • Data Blocks (DATA)
    • Acknowledgements (ACK)
    • Errors (ERROR)

    Trivial File Transfer Protocol (TFTP) Issues

    • Connectionless and unreliable UDP used (need for error control).
    • Time outs & retransmission required.
    • Packet loss in network may cause time-out & retransmission
    • Block numbering (data packet integrity)

    FTP Secure (FTPS)

    • Secure FTP protocol that encrypts files exchanged using SSL (Secure Sockets Layer).
    • Two types:
      • Explicit FTPS (port 21) encryption on data channel after authentication.
      • Implicit FTPS (port 990) encryption on command channels.
    • Encrypts file transfer with strong algorithms (AES and triple DES).
    • Authentication uses usernames/passwords &/or certificates.

    Secure File Transfer Protocol (SFTP)

    • Secure FTP protocol using SSH.
    • Offers high protection for file transfers using TCP port 22.
    • Uses strong encryption algorithms including AES, triple DES and others.
    • Authentication methods include user names/passwords, SSH keys, and combinations.

    Briefly contrasting SFTP and FTPS

    • FTPS can be difficult connecting to secured firewalls since it uses multiple port numbers (control & data channels).
    • SFTP is simpler, easier to configure firewalls since it uses a single port (port 22).
    • SFTP uses SSH keys allowing shared authentication between trading partners

    The choice - SFTP or FTPS

    • IT department and/or partners may dictate which protocol is used.
    • Authentication with certificates may be required by customers and partners
    • Firewall configuration can be a deciding factor.
    • Customers may only use one port which makes SFTP preferable.

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    FTP etc. PDF

    Description

    This quiz covers the essential concepts of File Transfer Protocol (FTP) including its architecture, authentication methods, and the importance of secure file transfer. Understand the significance of TCP connections and how FTP functions within various client setups. Test your knowledge on secure management practices and legacy system compatibility.

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