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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)       9  TCP/IP Key Applications and Application Protocols            9  TCP/IP File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)                 9  TCP/IP General File Transfer Protocols (FTP and TFTP)                      9  Trivial File Transfer Protocol (TFTP)

TFTP Detailed Operation and Messaging 1 2 3 4 TFTP Message Formats

TFTP Write Process With and Without Option Negotiation

The initial message exchange for a normal write (without option negotiation):

1. Client sends write request.
   
   
2. Server sends acknowledgment.
   
   
3. Client sends data block #1.
   
   
4. Server acknowledges data block #1.

…

And a write with option negotiation:

1. Client sends write request with options.
   
   
2. Server sends option acknowledgment (instead of regular acknowledgment).
   
   
3. Client sends data block #1.
   
   
4. Server acknowledges data block #1.

…

Table 234 contains a summary of the three TFTP options currently defined.

Table 234: TFTP Options

TFTP Option Name	TFTP Option Code (Used in Request Messages)	Defining RFC	Description
Block Size	blksize	2348	Allows the client and server to send data blocks of a size different than 512 bytes, to improve efficiency or address limitations of a particular type of network.
Timeout Interval	interval	2349	Permits the client and server to agree on a specified number of seconds to use for their retransmission timers. Again, may be of value on certain networks with high latency or other special requirements.
Transfer Size	tsize	2349	Lets the device sending the file (client on a write, server on a read) tell the other device the size of the file before the transfer commences. This allows the receiving device to allocate space for it in advance.

TFTP Detailed Operation and Messaging 1 2 3 4 TFTP Message Formats

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