TFTP Windowsize Option

This RFC 7440 was published in 2015.


The "Trivial File Transfer Protocol" (RFC 1350) is a simple, lockstep, file transfer protocol that allows a client to get or put a file onto a remote host.
One of its primary uses is in the early stages of nodes booting from a Local Area Network (LAN).
TFTP has been used for this application because it is very simple to implement.
The employment of a lockstep scheme limits throughput when used on a LAN.

RFC 7440 introduction

TFTP is virtually unused for Internet transfers today, TFTP is still massively used in network boot/installation scenarios including EFI (Extensible Firmware Interface).
TFTP's inherently low transfer rate has been, so far, partially mitigated by the use of the blocksize negotiated extension [RFC2348].
Using this method, the original limitation of 512-byte blocks are, in practice, replaced in Ethernet environments by blocks no larger than 1468 Bytes to avoid IP block fragmentation.
This strategy produces insufficient results when transferring big files, for example, the initial ramdisk of Linux distributions or the PE images used in network installations by Microsoft WDS/MDT/SCCM.
Considering TFTP looks far from extinction today, this document presents a negotiated extension, under the terms of the "TFTP Option Extension" [RFC2347], that produces TFTP transfer rates comparable to those achieved by modern file transfer protocols.

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