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- [Instructor] File transfer protocol, or FTP,

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has been used to transfer files since 1971.

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FTP relies on TCP for reliable delivery.

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FTP is great for plain text transmissions,

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but can also use TLS or SSL to encrypt the sessions.

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FTP can run in either active or passive modes.

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In both modes, the session is initiated on TCP port 21.

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In active mode, the client will inform the server

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on what port the server should access the client at.

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The server will then initiate a connection to the client

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from TCP port 20 for the data transfer.

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In most situations,

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a client's machine will be behind a firewall

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or utilize a software firewall,

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which will prevent incoming connections.

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If this is the case, passive mode should be used.

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In passive mode, the server provides a specific port

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for the client to connect to.

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The client then initiates the outbound connection

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to the server for data transfer.

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Trivial file transport protocol, or TFTP,

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is a light transfer protocol.

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Its nature is perfect for devices

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that pull their configuration on boot

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or as a service for network hardware

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to transfer firmware and configurations.

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It's used by IP phones, routers, switches,

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and many smaller devices attached to networks.

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TFTP utilizes UDP port 69,

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so it is a connectionless service.

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Being that it's a light protocol,

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it can't list, rename, delete files or directories.

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It also doesn't support any form of authentication.

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By default, files are transferred at 512 byte blocks,

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but the protocol can negotiate a larger block size.

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Each block is transferred in a single packet.

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After each block, an acknowledgement is sent back.

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If there is no acknowledgement,

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then the packet is retransmitted.

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Modern file sharing services and systems via browser

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have all but killed the need for dedicated FTP servers.

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When a user is in a remote area

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and just needs to transfer a file somewhere else,

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it can still be an invaluable resource.