The TCP/IP Guide - TFTP Message Formats

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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 Options and Option Negotiation

TCP/IP Electronic Mail System: Concepts and Protocols (RFC 822, MIME, SMTP, POP3, IMAP)

TFTP Message Formats
(Page 3 of 5)

Data Messages

Data blocks are sent using the simplified format shown in Table 236 and Figure 297.

**Table 236: TFTP *Data* Message Format**
Field Name	Size (bytes)	Description
*Opcode*	2	*Operation Code:* Specifies the TFTP message type. A value of 3 indicates a Data message.
*Block #*	2	*Block Number:* The number of the data block being sent.
*Data*	Variable	*Data:* 0 to 512 bytes of data.

**Figure 297: TFTP *Data* Message Format**

Acknowledgment Messages

Acknowledgments have the simplest format of any TFTP message, as you can see in Table 237 and Figure 298.

**Table 237: TFTP *Acknowledgment* Message Format**
Field Name	Size (bytes)	Description
*Opcode*	2	*Operation Code:* Specifies the TFTP message type. A value of 4 indicates an Acknowledgment message.
*Block #*	2	*Block Number:* The number of the data block being acknowledged; a value of 0 is used to acknowledge receipt of a write request without options, or to acknowledge receipt of an option acknowledgment.

**Figure 298: TFTP *Acknowledgment* Message Format**

TFTP Options and Option Negotiation

TCP/IP Electronic Mail System: Concepts and Protocols (RFC 822, MIME, SMTP, POP3, IMAP)

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