25.02.2013 Views

TCP/IP Tutorial and Technical Overview - IBM Redbooks

TCP/IP Tutorial and Technical Overview - IBM Redbooks

TCP/IP Tutorial and Technical Overview - IBM Redbooks

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

14.2.4 Data modes<br />

The TFTP header contains the opcode associated with the packet. See<br />

Figure 14-7 for more details.<br />

RRQ/WRQ<br />

packet<br />

Data packet<br />

ACK packet<br />

Error packet<br />

OACK packet<br />

Figure 14-7 TFTP packet headers<br />

Two modes of transfer are currently defined in RFC 1350:<br />

NetASCII US-ASCII, as defined in the USA St<strong>and</strong>ard Code for Information<br />

Interchange with modifications specified in RFC 854 – Telnet<br />

Protocol Specification <strong>and</strong> extended to use the high order bit.<br />

(That is, it is an 8-bit character set, unlike US-ASCII, which is<br />

7-bit.)<br />

Octet Raw 8-bit bytes, also called binary.<br />

The mode used is indicated in the TFTP header for the Request for Read/Write<br />

packets (RRQ/WRQ).<br />

14.2.5 TFTP multicast option<br />

The TFTP multicast option enables multiple clients to get files simultaneously<br />

from the server using the multicast packets. For example, when two similar<br />

machines are remotely booted, they can retrieve the same configuration file<br />

simultaneously by adding the multicast option to the TFTP option set. The TFTP<br />

532 <strong>TCP</strong>/<strong>IP</strong> <strong>Tutorial</strong> <strong>and</strong> <strong>Technical</strong> <strong>Overview</strong><br />

2 bytes string 1 byte string 1 byte<br />

Opcode = 1/2 Filename 0 Mode 0<br />

2 bytes 2 bytes up to 512 bytes<br />

Opcode = 3 Block # Data<br />

2 bytes 2 bytes<br />

Opcode = 4 Block #<br />

2 bytes 2 bytes string 1 byte<br />

Opcode = 5 Block # Error message 0<br />

Opcode=6 opt1 0 val1 0 optN 0 valN 0

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!