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<p class="MsoNormal">I partially agree with you, but… 10 is way too aggressive. I’m already seeing a “true” internet diameter of up to 13 AS hops today. Here’s the data I’m using to form that opinion.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">[ NOTE: my tooling didn’t handle BGP confederations in the RIB dump properly. It’s sufficiently rare (only 1009 routes in total) that I’m not going back to square one to compensate for that, the data’s not noticeably skewed because of
it, with one exception: the len=15 and len=16 entries in the de-prepended tale are both bogus. I left them in in the spirit of full disclosure. ]<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This is the AS path-length distribution in my RIB as of a few minutes ago. Like everyone else, I do some moderately strange things for <reasons> including artificially locally prepending routes from some of my upstreams, so I’m quite certain
no-one else’s will exactly match mine. The overall shape of the distribution, though, should be very similar, probably with the peak shifted left or right slightly.<o:p></o:p></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Pathlen<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Count<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">1<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">1864<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">2<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">77314<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">3<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">223030<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">4<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">248878<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">5<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">729240<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">6<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">627685<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">7<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">224092<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">8<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">105225<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">9<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">60962<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">10<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">50201<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">11<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">22856<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">12<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">11914<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">13<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">7224<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">14<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">5423<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">15<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">4421<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">16<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">2756<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">17<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">1577<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">18<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">945<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">19<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">422<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">20<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">669<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">21<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">477<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">22<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">116<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">23<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">70<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">24<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">75<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">25<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">163<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">26<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">33<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">27<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">40<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">28<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">5<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">29<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="mso-fareast-language:EN-US">30<o:p></o:p></span></p>
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<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">5<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">31<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">5<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">33<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">1<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">35<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">12<o:p></o:p></span></p>
</td>
</tr>
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<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">38<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">5<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">39<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">2<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">40<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">1<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">55<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">1<o:p></o:p></span></p>
</td>
</tr>
</tbody>
</table>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I took a look at some of the outliers, and they are, in the extreme cases, somewhat insane, with over 20 prepends or more in those last few cases. However, at least a few of the pathlen>=20 entries
could be legit. Could be. Not saying they are, just that there are some paths that aren’t immediately obvious BS and it would take a lot more time & effort to figure that out.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I then eliminated ALL the prepends, remote, and local and transit, and that length distribution changes to look like this, which should reflect the “true” diameter of the internet as seen from here:<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<table class="MsoNormalTable" border="0" cellspacing="0" cellpadding="0" style="border-collapse:collapse">
<tbody>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Pathlen<o:p></o:p></span></p>
</td>
<td valign="top" style="border:solid windowtext 1.0pt;border-left:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Count<o:p></o:p></span></p>
</td>
</tr>
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<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">1<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">18950<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">2<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">223149<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">3<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">563843<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">4<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">824648<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">5<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">532985<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">6<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">165056<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">7<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">47559<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">8<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">16759<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">9<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">8430<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">10<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">3746<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">11<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">519<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">12<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">233<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">13<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">6<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">15<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">1<o:p></o:p></span></p>
</td>
</tr>
<tr>
<td valign="top" style="border:solid windowtext 1.0pt;border-top:none;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">16<o:p></o:p></span></p>
</td>
<td valign="top" style="border-top:none;border-left:none;border-bottom:solid windowtext 1.0pt;border-right:solid windowtext 1.0pt;padding:0in 5.4pt 0in 5.4pt">
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">2<o:p></o:p></span></p>
</td>
</tr>
</tbody>
</table>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">(Interestingly, the
<i>shape</i> of the distribution doesn’t change significantly. That hints that most people could be doing prepending in roughly the same way.)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Using your suggestion of as AS-PATH length of 10 as a cutoff, you’d be dropping ~4.5% (109,460 routes here) of the total RIB. But even in my artificially de-prepended dataset, I still see 4,507
presumably-legitimate routes with a path length >= 10.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I’m not saying a threshold is a bad idea. (I’m on the fence.) I AM saying that using 10 as your cutoff point is too aggressive, and in my opinion,
<i>way</i> too aggressive.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Based on the de-prepended dataset, the approximate diameter of
<i>my</i> internet (not necessarily yours) is 13 AS hops. (Not 15 or 16, see note above.)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Since it’s entirely public data, here’s the raw paths from me to AS 270606, prepends and all, that generated my “true” diameter of 13, as recorded in my looking glass:<o:p></o:p></span></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span style="mso-fareast-language:EN-US">I* N 177.37.16.0/22 206.211.216.51 100 0 7122 7122 577 6461 52320 53087 262740 262740 262740 262740 262740 262740 266097 268868 61568 26615
10429 263144 270606<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span style="mso-fareast-language:EN-US">I* N 177.37.16.0/22 206.211.216.52 100 0 7122 7122 577 6461 52320 53087 262740 262740 262740 262740 262740 262740 266097 268868 61568 26615
10429 263144 270606<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span style="mso-fareast-language:EN-US">I* N 177.37.16.0/22 216.73.71.131 100 0 6327 6327 6327 6461 52320 53087 262740 262740 262740 262740 262740 262740 266097 268868 61568 26615
10429 263144 270606<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">(Formatting didn’t translate well… the locally-prepended AS path for these 3 examples starts with 7122 7122 577, or 6327 6327 6327.)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I do not have <u>any</u> alternate path to those prefixes in my RIB. The deduped 13-long path is “7122 577 6461 52320 53087 262740 266097 268868 61568 26615 10429 263144 270606”.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Do I really care if education users in Manitoba can reach R3 Telecom users in Brazil? Probably not (although there
<i>are</i> quite a lot of Brazilian international students here, so maybe?) but this demonstrates that the “diameter of the internet” is absolutely not well under 10.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I’ll point out, since I speculated about this in a previous email, the most extreme case discussed here was purely on commercial internet, and did not involve NREN paths at all. I went looking for
NREN-style prepending and found several examples buried in the middle of the distribution. That presumptive root cause doesn’t appear, at least at first glance, to contribute much to the extreme path lengths I see.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Imposing a limit like this has a strong precedent: Sprint(?)’s cap at accepting only /24 and larger, waaaaaay back. Like that action, this max-path-len proposal is likely to be discriminatory because
it implicitly favours ASNs located in areas with good connectivity to the “core”, i.e. mainly the eastern US and some areas of western Europe. (I also did not examine the entire path to AS270606 for sanity – it’s not always about simple availability, sometimes
perverse incentives play a strong role, too.)<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">If I start looking at the 233 routes of “true” distance 12, where will they be located? Or the 519 at 11? Remember, those are already the de-prepended paths. I don’t want to have to police the
RIB that tightly, deciding which routes I will and won’t accept and adjusting the limit periodically.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">Unless your intent is to eliminate prepend-based traffic engineering from the internet altogether, which case 10 is a perfectly reasonable choice, but in the absence of any other globally-usable
tool/knob, that’s a hill I WILL die on.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">If there’s broad consensus that a path length limit is a good thing, I would suggest a value of no less than 32, based on the data I’ve got in my RIB right now. I think, based only on random sampling
of longer AS paths in my RIB, that 32 would still give operators the latitude to perform AS-path-based traffic engineering at origin, during transit, and locally upon receipt, without routes getting inexplicably blackholed anywhere.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">I’ve heard tonight that a path length limit of 32 is already commonly implemented. Regardless of whether I think that’s a good idea, the spectre of the stack-breakingly-long path seems to be already
mitigated in many places, but perhaps not widely?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">To sum up, Tom’s conclusions as expressed in his email (below) may be
<i>qualitatively</i> correct, but they are <i>quantitatively</i> wrong, at least on the matter of the numeric threshold. And… I don’t really want to be the next Sprint(?) in BGP history just to protect myself from newbies on Mikrotiks[1], do you?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">-Adam<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US">[1] and others, yes, I know it’s not purely a Mikrotik issue.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;color:#44546A;background:white">Adam Thompson</span></b><span style="font-size:9.0pt;color:#44546A;background:white"><br>
Consultant, Infrastructure Services<br>
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<a href="http://www.merlin.mb.ca/" target="_blank">www.merlin.mb.ca</a></span><span style="font-size:12.0pt;color:black"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="mso-fareast-language:EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> Tom Beecher <beecher@beecher.cc>
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<b>Sent:</b> Saturday, March 26, 2022 11:35 AM<br>
<b>To:</b> Adam Thompson <athompson@merlin.mb.ca><br>
<b>Cc:</b> Paschal Masha <paschal.masha@ke.wananchi.com>; nanog <nanog@nanog.org><br>
<b>Subject:</b> Re: DMARC ViolationAS21299 - 46.42.196.0/24 ASN prepending 255 times<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Mostly what Matt said. ( I should have also said 'ride the 0/0 train INTO the DFZ, my mistake.)<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Essentially, if ASN X is announcing a prefix with an excessive number of prepends, they are saying to the world 'This path exists , but it is hot garbage.' I'm more than happy to oblige those instructions and just drop that announcement
completely. If ASN X announces that prefix with a reasonable number of prepends, happy to take it and use it. <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">If I get a prefix with an as-path longer than 10, (regardless of the state of prepends), I interpret that as : <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">1. They have made a mistake. <o:p></o:p></p>
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<p class="MsoNormal">2. Someone else made a mistake.<o:p></o:p></p>
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<p class="MsoNormal">3. They think that's a good idea, and have some things yet to learn. ( The old clue by four as Matt put it.)<o:p></o:p></p>
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<p class="MsoNormal">4. It's malicious. <o:p></o:p></p>
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<p class="MsoNormal">5. They actually are somehow more than 10 ASNs away from me. ( I don't even know if this is possible anymore without extreme effort. )<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">In any of those scenarios , I don't really care about optimized routing to that destination. Perfectly happy to just follow 0/0 to a DFZ upstream and let it go how it's going to go, or not. If there is a traffic impact such that an exception
HAS to be made, that can be addressed as needed, but I can't think of a single circumstance I have hit where the correction involved accepting an obnoxiously long as_path announcement. ( I don't mean to imply none exist ; I'm sure someone has had to work though
that. ) <o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Maybe a length of 10 doesn't work for some environments and use cases, but I still am a firm believer that at a certain point, there is a length that becomes straight 'really don't care'. I'd rather not discover a BGP implementation problem
or acid trip memory pointer party by accepting announcements that are useless.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">On Fri, Mar 25, 2022 at 5:56 PM Adam Thompson <<a href="mailto:athompson@merlin.mb.ca">athompson@merlin.mb.ca</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">Tom, how exactly does someone “ride the 0/0” train in the DFZ?<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">I’m connected to both commercial internet and NREN, and unfortunately-long paths are not uncommon in this scenario, in order to do traffic steering. If there’s another solution
that affects global <i>inbound</i> traffic distributions, I’d love to hear about it (and so would a lot of my peers in edu).<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">If there were a usable way to “dump” the excessively-long path only as long as a better path was already known by at least one edge router, that might be workable, but you’d have
to keep track of it somewhere to reinstall it if the primary route went away… at which point you may as well have not dropped it in the first place.<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">-Adam<o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span style="font-size:10.0pt;color:#44546A;background:white">Adam Thompson</span></b><span style="font-size:9.0pt;color:#44546A;background:white"><br>
Consultant, Infrastructure Services<br>
<img border="0" width="128" height="39" style="width:1.3333in;height:.4083in" id="gmail-m_-9097733568303205974Picture_x0020_1" src="cid:image001.png@01D843A7.A794B5D0" alt="MERLIN"><br>
100 - 135 Innovation Drive<br>
Winnipeg, MB, R3T 6A8<br>
(204) 977-6824 or 1-800-430-6404 (MB only)<br>
<a href="mailto:athompson@merlin.mb.ca" target="_blank">athompson@merlin.mb.ca</a><br>
<a href="http://www.merlin.mb.ca/" target="_blank">www.merlin.mb.ca</a></span><o:p></o:p></p>
<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> NANOG <nanog-bounces+athompson=<a href="mailto:merlin.mb.ca@nanog.org" target="_blank">merlin.mb.ca@nanog.org</a>>
<b>On Behalf Of </b>Tom Beecher<br>
<b>Sent:</b> Friday, March 25, 2022 4:13 PM<br>
<b>To:</b> Paschal Masha <<a href="mailto:paschal.masha@ke.wananchi.com" target="_blank">paschal.masha@ke.wananchi.com</a>><br>
<b>Cc:</b> nanog <<a href="mailto:nanog@nanog.org" target="_blank">nanog@nanog.org</a>><br>
<b>Subject:</b> Re: DMARC ViolationAS21299 - <a href="http://46.42.196.0/24" target="_blank">
46.42.196.0/24</a> ASN prepending 255 times</span><o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">The best practice with regards to as_path length is to have an edge filter that dumps any prefix with a length longer than say 10. Depending on the situation, might even be able
to go smaller. <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">At a certain point, keeping that route around does nothing for you, just shoot it and ride the 0/0 train. <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto"> <o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;mso-margin-bottom-alt:auto">On Fri, Mar 25, 2022 at 4:09 AM Paschal Masha <<a href="mailto:paschal.masha@ke.wananchi.com" target="_blank">paschal.masha@ke.wananchi.com</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="mso-margin-top-alt:auto;margin-bottom:12.0pt">:) probably the longest prepend in the world.<br>
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A thought though, is it breaking any standard or best practice procedures?<br>
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Regards <br>
Paschal Masha | Engineering <br>
Skype ID: paschal.masha<br>
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----- Original Message -----<br>
From: "Erik Sundberg" <<a href="mailto:ESundberg@nitelusa.com" target="_blank">ESundberg@nitelusa.com</a>><br>
To: "nanog" <<a href="mailto:nanog@nanog.org" target="_blank">nanog@nanog.org</a>><br>
Sent: Friday, March 25, 2022 6:43:38 AM<br>
Subject: DMARC ViolationAS21299 - <a href="http://46.42.196.0/24" target="_blank">
46.42.196.0/24</a> ASN prepending 255 times<br>
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If anyone from AS21299 is lurking on Nanog. Please reduce your AS prepends for <a href="http://46.42.196.0/24" target="_blank">
46.42.196.0/24</a> from 255 prepends to a more reasonable number of prepends let's say 20. Thanks!
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This is a Kazakhstan register IP Block and ASN <br>
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Network Next Hop Metric LocPrf Weight Path <br>
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*> <a href="http://46.42.196.0/24" target="_blank">46.42.196.0/24</a> x.x.x.x 0 100 0 2914 174 3216 3216 35168 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299
21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299
21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299
21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299
21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299
21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299
21299 21 299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 21299 i
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Thank you. <br>
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