<html><head><meta http-equiv="Content-Type" content="text/html; charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Just because there is a small code snippet you found that prevents casting 240/4 as unicast on an interface doesn’t mean that removing that code will magically make 240/4 usable in the entire stack.<div class=""><br class=""></div><div class="">It’s also important to note that there are at least a dozen IPv4 stacks in common use with differing code implementations and underlying assumptions baked into the code in various places. Your Q.E.D. is, in fact, a demonstration of the fact that you are still lack some background and experience in networking software.<br class=""><div><br class=""></div><div>The code you found may just be a safety valve to prevent the user from doing something stupid that will have undefined consequences down the line if executed. What you appear to have found is, quite likely, the equivalent of a buffer bounds check on input. Removing the check doesn’t inherently make the buffer infinite.</div><div><br class=""></div><div>Owen</div><div><br class=""><blockquote type="cite" class=""><div class="">On Mar 26, 2022, at 09:38 , Abraham Y. Chen <<a href="mailto:aychen@avinta.com" class="">aychen@avinta.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class="">
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<div class="moz-cite-prefix"><font size="4" class="">Hi, Paul:</font></div>
<div class="moz-cite-prefix"><font size="4" class=""><br class="">
</font></div>
<div class="moz-cite-prefix"><font size="4" class="">1) " ... may be in
fact: /writing/* and */deploying/* the code ... ": Having no
idea why and how the 240/4 netblock became so mysteriously kept
away from being used while the IPv4 was officially already on
its way to "Sun Set", we started the conventional approach as
you stated. It was quite frustrating since we did not have the
background in networking software. One day, we came across a
short program code fragment that did the function of <i class=""><b class="">disabling</b></i>
240/4 addressed IP packets. It is the "there exists an example"
moment for us, like proofing a mathematics theorem. After all,
there was no magic separating 240/4 from the rest of the IPv4
address pool to start with. </font><font size="4" class=""><font size="4" class="">It cleared our mind about this particular task.</font>
Now, we only cite this reference to challenge those software
engineers who may state that using the 240/4 in their code is a
lot more involved. .... Q.E.D. 😉</font></div>
<div class="moz-cite-prefix"><font size="4" class=""><br class="">
</font></div>
<div class="moz-cite-prefix"><font size="4" class="">Regards,</font></div>
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</font></div>
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</font></div>
<div class="moz-cite-prefix"><font size="4" class="">Abe (2022-03-26 12:37
EDT)</font><br class="">
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<div class="moz-cite-prefix">On 2022-03-26 09:52, Paul Rolland
wrote:<br class="">
</div>
<blockquote type="cite" cite="mid:20220326145215.2148cc0c@riri.witbe.net" class="">
<pre class="moz-quote-pre" wrap="">Hello,
On Sat, 26 Mar 2022 09:35:30 -0400
"Abraham Y. Chen" <a class="moz-txt-link-rfc2396E" href="mailto:aychen@avinta.com"><aychen@avinta.com></a> wrote:
</pre>
<blockquote type="cite" class="">
<pre class="moz-quote-pre" wrap="">touching the hardware, by implementing the EzIP technique (*/disabling/*
the program code that has been */disabling/* the use of the 240/4
netblock), an existing CG-NAT module becomes a RAN! As to universal
</pre>
</blockquote>
<pre class="moz-quote-pre" wrap="">Have you ever considered that this may be in fact:
*/writing/* and */deploying/* the code that will allow the use of 240/4 the
way you expect
Paul
</pre>
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