RFC 2348 (rfc2348) - Page 2 of 5

TFTP Blocksize Option

RFC 2348                 TFTP Blocksize Option                  May 1998


      filename
         The name of the file to be read or written, as defined in [1].

      mode
         The mode of the file transfer: "netascii", "octet", or "mail",
         as defined in [1].

      blksize
         The Blocksize option, "blksize" (case in-sensitive).

      #octets
         The number of octets in a block, specified in ASCII.  Valid
         values range between "8" and "65464" octets, inclusive.  The
         blocksize refers to the number of data octets; it does not
         include the four octets of TFTP header.

   For example:

      +-------+--------+---+--------+---+--------+---+--------+---+
      |   1   | foobar | 0 | octet  | 0 | blksize| 0 |  1428  | 0 |
      +-------+--------+---+--------+---+--------+---+--------+---+

   is a Read Request, for the file named "foobar", in octet (binary)
   transfer mode, with a block size of 1428 octets (Ethernet MTU, less
   the TFTP, UDP and IP header lengths).

   If the server is willing to accept the blocksize option, it sends an
   Option Acknowledgment (OACK) to the client.  The specified value must
   be less than or equal to the value specified by the client.  The
   client must then either use the size specified in the OACK, or send
   an ERROR packet, with error code 8, to terminate the transfer.

   The rules for determining the final packet are unchanged from [1].
   The reception of a data packet with a data length less than the
   negotiated blocksize is the final packet.  If the blocksize is
   greater than the amount of data to be transfered, the first packet is
   the final packet.  If the amount of data to be transfered is an
   integral multiple of the blocksize, an extra data packet containing
   no data is sent to end the transfer.

Proof of Concept

   Performance tests were run on the prototype implementation using a
   variety of block sizes.  The tests were run on a lightly loaded
   Ethernet, between two HP-UX 9000, in "octet" mode, on 2.25MB files.
   The average (5x) transfer times for paths with (g-time) and without
   (n-time) a intermediate gateway are graphed as follows:




Malkin & Harkin             Standards Track