TFTP Timeout Interval and Transfer Size Options

This document updates RFC 1350 (TFTP Protocol Revision 2) and relies on the TFTP Option Extension mechanism defined in RFC 1782. Implementations must be familiar with both base specifications to use these options.

If the server accepts the timeout option, it sends an Option Acknowledgment (OACK) to the client, and the timeout value in the OACK must match the value specified by the client.

In a Read Request, the client specifies a tsize value of '0'; the server returns the actual file size in octets in the OACK. If the file is too large for the client to handle, it may abort the transfer with Error packet error code 3.

In a Write Request, the client specifies the file size in octets as the tsize value; the server echoes it back in the OACK. If the file is too large for the server to handle, it may abort the transfer with Error packet error code 3.

Valid timeout interval values range between '1' and '255' seconds, inclusive, specified in ASCII.

The timeout option name is the ASCII string 'timeout' (case insensitive), NULL-terminated. Its value is the number of seconds to wait before retransmitting, encoded as a NULL-terminated ASCII decimal string.

The transfer size option name is the ASCII string 'tsize' (case insensitive), NULL-terminated. Its value is the file size in octets, encoded as a NULL-terminated ASCII decimal string.

Security issues are not discussed in this memo.

security

The TFTP RRQ or WRQ packet is extended with the 'tsize' option by appending the NULL-terminated string 'tsize' followed by a NULL-terminated ASCII decimal value representing file size in octets. All fields are NULL-terminated strings appended after the standard mode field.