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<p>I think that is required by SLAAC RFC, which adds another 2 bytes
to 6 bytes of hardware ethernet address.</p>
<p>Which is in total 8 bytes, therefore 64 bits is required for it.
Prefix cannot be higher, but can be lower in theory. There might
be some implementation details now supporting lower prefix length
in current implementation.</p>
<p>Cheers,<br>
Petr<br>
</p>
<div class="moz-cite-prefix">On 15. 06. 23 12:07, renmingshuai via
Dnsmasq-discuss wrote:<br>
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<p class="MsoNormal" style="line-height:130%"><span lang="EN-US">When
ra-only, slaac, or ra-stateless is configured in dhcp-range
and the prefix len is set to a value other than 64, like
this:<o:p></o:p></span></p>
<p class="MsoNormal" style="line-height:130%"><span lang="EN-US">“dhcp-range=2000:1000:1000:1000:1000:1000::,
ra-stateless,120,infinite”<o:p></o:p></span></p>
<p class="MsoNormal" style="line-height:130%"><span lang="EN-US">the
following error message is displayed:<o:p></o:p></span></p>
<p class="MsoNormal" style="line-height:130%"><span lang="EN-US">dnsmasq:
prefix length must be exactly 64 for RA subnets at line 16
of /etc/dnsmasq.conf<o:p></o:p></span></p>
<p class="MsoNormal" style="line-height:130%"><span lang="EN-US">Why
must the prefix length be 64? This may come from an RFC
regulation or recommendation, but I didn't find it. Would
you mind tell me the reason?<o:p></o:p></span></p>
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<pre class="moz-signature" cols="72">--
Petr Menšík
Software Engineer, RHEL
Red Hat, <a class="moz-txt-link-freetext" href="http://www.redhat.com/">http://www.redhat.com/</a>
PGP: DFCF908DB7C87E8E529925BC4931CA5B6C9FC5CB</pre>
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