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<a href="https://gitlab.rtems.org/tracmigrate">Trac Migrate</a> created an issue: <a href="https://gitlab.rtems.org/rtems/pkg/rtems-net-legacy/-/issues/14">#14</a>
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Assignee: Trac Migrate
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<p dir="auto" style="color: #28272d; margin: 0 0 16px;" align="initial">Original author: timcussins</p>
<p dir="auto" style="color: #28272d; margin: 0 0 16px;" align="initial">The dhcp code in rtems uses an unchanging transaction id (xid) in the dhcp discover and request packets.</p>
<p dir="auto" style="color: #28272d; margin: 0 0 16px;" align="initial">It is possible (and in fact has been observed) that dhcp servers may issue multiple OFFER packets in response to multiple REQUEST packets from the same device.</p>
<p dir="auto" style="color: #28272d; margin: 0 0 16px;" align="initial">The second OFFER packet could potentially be received while the dhcp state machine is waiting for an ACK packet - and this would cause the rtems dhcp process to fail needlessly.</p>
<p dir="auto" style="color: #28272d; margin: 0 0 16px;" align="initial">A solution to this is to use the transaction id field (described in the bootp/dhcp protocols) to match server dhcp replies with rtems dhcp requests.</p>
<p dir="auto" style="color: #28272d; margin: 0 0 16px;" align="initial">For details on the use of xid, see RFC 2131, Section 4.4.1 (<a href="http://www.networksorcery.com/enp/rfc/rfc2131.txt" rel="nofollow noreferrer noopener" target="_blank" style="margin-top: 0;">http://www.networksorcery.com/enp/rfc/rfc2131.txt</a>)</p>
<p dir="auto" style="color: #28272d; margin: 0 0 16px;" align="initial">The patch creates a unique xid for each dhcp transaction: the DISCOVER/OFFER and REQUEST/ACK phases use different xid's, there is no confusion in the rtems state machine.</p>
<ul dir="auto" style="text-align: initial; list-style-type: disc; margin: 0; padding: 0;">
<li style="margin-top: 0; line-height: 1.6em; margin-left: 25px; padding-left: 3px;"><a href="https://gitlab.rtems.org/rtems/pkg/rtems-net-legacy/-/blob/main/assets/tracmigration/ticket_attachments/0001-libnetworking-rtems_dhcp.c-Fix-invariant-DHCP-transa.patch" class="gfm" style="margin-top: 0;">0001-libnetworking-rtems_dhcp.c-Fix-invariant-DHCP-transa.patch</a></li>
<li style="line-height: 1.6em; margin-left: 25px; padding-left: 3px;"><a href="https://gitlab.rtems.org/rtems/pkg/rtems-net-legacy/-/blob/main/assets/tracmigration/ticket_attachments/dhcp-unique-xid.diff" class="gfm" style="margin-top: 0;">dhcp-unique-xid.diff</a></li>
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