109 lines
6.9 KiB
HTML
109 lines
6.9 KiB
HTML
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<meta name="DC.Title" content="Server-to-client TFTP Option Acknowledgment" />
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<meta name="abstract" content="The TFTP server sends an Option Acknowledgment (OACK) to a client in response to either a read request or a write request that includes additional TFTP options as described in Client to server TFTP Read Request (RRQ) options." />
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<meta name="description" content="The TFTP server sends an Option Acknowledgment (OACK) to a client in response to either a read request or a write request that includes additional TFTP options as described in Client to server TFTP Read Request (RRQ) options." />
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<meta name="DC.Relation" scheme="URI" content="rzal5rrqoptions.htm" />
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<title>Server-to-client TFTP Option Acknowledgment</title>
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</head>
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<body id="rzal5oack"><a name="rzal5oack"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Server-to-client TFTP Option Acknowledgment</h1>
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<div><p>The TFTP server sends an Option Acknowledgment (OACK) to a client
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in response to either a read request or a write request that includes additional
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TFTP options as described in Client to server TFTP Read Request (RRQ) options.</p>
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<div class="section"><p>An OACK that the servers sends in response to a transfer request
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includes only responses to requested options that the server supports. The
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server can also send an OACK to a client subsequently to the start of a subnet
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broadcast transfer. This is done to indicate to the client whether it is the
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master client in a subnet broadcast file group. An OACK packet that the server
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sends subsequently to the start of a subnet broadcast transfer includes the
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sbroadcast option.</p>
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<p>The following is a list of supported options and
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their descriptions:</p>
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<dl><dt class="dlterm"><strong>blksize</strong></dt>
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<dd>Null (0h) terminated <tt>blksize</tt> keyword that is followed by the
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block size that is used for this file transfer. It is represented as a null-terminated
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ASCII string. This is the response to a requested block size, and the value
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returned here can be less than the requested block size. The server determines
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the block size for the transfer based on the requested block size, the maximum
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configured block size, and possibly the subnet broadcast transfers that are
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already in progress.</dd>
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<dt class="dlterm"><strong>sbroadcast</strong></dt>
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<dd>Null-terminated <tt>sbroadcast</tt> keyword that is followed by a null-terminated
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ASCII string that includes the following fields separated by commas: <dl><dt class="dlterm">port</dt>
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<dd>The ASCII representation of the port to which the subnet-directed broadcast
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datagrams are broadcast. This is the well-known port that is registered with
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the Internet Assigned Number Authority (IANA) with the keyword of <tt>subntbcst_tftp</tt> and
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a decimal value of <tt>247</tt>. This field might be empty in OACK packets
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that the server sends subsequently to the start of a subnet broadcast transfer.</dd>
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<dt class="dlterm">sbid</dt>
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<dd>The ASCII representation of a decimal number that is called the <tt>subnet
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broadcast identifier</tt>. Possible values are 0 through 4 294 967 295
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(FFFFFFFFh). This is used along with the server source port to determine if
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a subnet-directed broadcast datagram is part of a requested transfer. This
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field can be empty in OACK packets that the server sends subsequently to the
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start of a subnet-based broadcast transfer.</dd>
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<dt class="dlterm">mc</dt>
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<dd>This is either an ASCII (31h) <tt>1</tt> or ASCII <tt>0</tt> (32h) to
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indicate to the client whether it is currently the master client. A value
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of <tt>1</tt> indicates that the client is the master client, and a value
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of <tt>0</tt> indicates that the client is not the master client. <p>In response
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to an OACK, the master client must send an ACK to the server. The master client
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sets the block number in this ACK to the number of the block prior to the
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first block that is required by the master client.</p>
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<p>The master client
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acknowledges subnet broadcast data (BDATA) packets by sending an ACK to the
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server. The master client sets the block number in this ACK to the block prior
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to the current block that the master client requires.</p>
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<p>Clients that are
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not indicated as being the master client respond to an OACK packet with an
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ACK that has the block number set to zero.</p>
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<div class="note"><span class="notetitle">Note:</span> The block number in ACK
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packets is the 2-byte binary representation of the number in network byte
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order.</div>
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</dd>
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</dl>
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</dd>
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<dt class="dlterm"><strong>tsize</strong></dt>
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<dd>The null-terminated <tt>tsize</tt> keyword that is followed by the null-terminated
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ASCII representation of the decimal number that represents the file size of
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the requested file. The client uses this information to ensure that it has
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enough space to store the file and to determine the last block number of the
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file. <div class="note"><span class="notetitle">Note:</span> The client can also determine the file size and last block of
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a transfer when it receives a block that contains less data than the block
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size.</div>
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</dd>
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</dl>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzal5tftpsub.htm" title="Broadcast storms are a performance problem that might occur when there are large numbers of systems that boot from the network.">TFTP Subnet Broadcast option</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rzal5rrqoptions.htm" title="This information includes the additional TFTP options that are supported and a description of their use.">Client-to-server TFTP Read Request options</a></div>
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</div>
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</div>
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</body>
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