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<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New";color:#441D61">Sorry, I did not intend to imply that you were.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New";color:#441D61">I should have prefaced my post with "to add".<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New";color:#441D61"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:#441D61">Regards,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:#441D61">Jakob.<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.0pt;font-family:"Courier New";color:#441D61"><o:p> </o:p></span></p>
<p class="MsoNormal"><b>From:</b> Matthew Petach <mpetach@netflight.com> <br>
<b>Sent:</b> Wednesday, April 15, 2020 4:29 PM<br>
<b>To:</b> Jakob Heitz (jheitz) <jheitz@cisco.com><br>
<b>Cc:</b> nanog@nanog.org<br>
<b>Subject:</b> Re: Route aggregation w/o AS-Sets<o:p></o:p></p>
<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">I apologize if I wasn't clear.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I don't recommend ever using AS_SET.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">So, in rule 3, I use the atomic-aggregate knob <o:p></o:p></p>
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<p class="MsoNormal">to announce the single covering aggregate with <o:p></o:p></p>
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<p class="MsoNormal">my backbone ASN as the atomic-aggregate origin <o:p></o:p></p>
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<p class="MsoNormal">AS, and I don't generate or propagate any AS_SET <o:p></o:p></p>
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<p class="MsoNormal">information along with the aggregate.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">That way, no loop is seen by any of the downstream <o:p></o:p></p>
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<p class="MsoNormal">networks that are announced the aggregate prefix.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">I hope that helps clear up what I meant in my third<o:p></o:p></p>
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<p class="MsoNormal">rule. :)<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Thanks!<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">Matt<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 Wed, Apr 15, 2020 at 11:26 AM Jakob Heitz (jheitz) via NANOG <<a href="mailto:nanog@nanog.org">nanog@nanog.org</a>> wrote:<o:p></o:p></p>
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<p class="MsoNormal" style="margin-bottom:12.0pt">Suppose you had a set of customers than all announced to you a set of routes<br>
and all those routes complete an aggregate<br>
and you announce only the aggregate to those customers<br>
and you include an AS_SET with it<br>
then those customers will drop your aggregate, thinking there is an AS-loop<br>
and those customers will not be able to reach each other.<br>
<br>
An AS_SET does not prevent routing loops and can prevent correct routing.<br>
<br>
But you must include the ATOMIC_AGGREGATE attribute, so that someone else<br>
does not disaggregate your aggregate that does not have the AS_SET.<br>
<br>
Regards,<br>
Jakob.<br>
<br>
-----Original Message-----<br>
Date: Tue, 14 Apr 2020 02:32:37 -0700<br>
From: Matthew Petach <<a href="mailto:mpetach@netflight.com" target="_blank">mpetach@netflight.com</a>><br>
<br>
I generally would use the atomic-aggregate knob to<br>
generate aggregate routes for blocks I controlled,<br>
when the downstream ASN information was not<br>
necessary to propagate outside my network<br>
(usually cases where I had multiple internal ASNs,<br>
but all connectivity funneled though a single upstream pathway.)<br>
<br>
If you have discrete downstream ASNs with potentially<br>
different external pathways, you shouldn't be generating<br>
aggregate routes that cover them; that's just bad routing 101.<br>
<br>
Thus, my rules for aggregation always came down to:<br>
1) is there more than one external/upstream pathway for the ASN and prefix?<br>
<br>
If so, don't aggregate.<br>
2) is redundant, reliable connectivity between all the external gateway<br>
routers that would be announcing the aggregate?<br>
If not, don't generate a covering aggregate.<br>
3) If there's only a single upstream pathway through you for the ASN and<br>
prefix,<br>
and that won't be changing any time soon (eg, you have a collection of<br>
downstream<br>
datacenter with their own ASNs and prefixes, but they all route through a<br>
common<br>
backbone), then use the atomic-aggregate option to suppress the more<br>
specific<br>
AS_PATH information, and simply announce the space as a single aggregate<br>
coming<br>
from your backbone ASN.<br>
<br>
That way, there's no confusion with RPKI and AS_SETS; all you're ever<br>
announcing<br>
are simple AS_PATHs for a given prefix.<br>
<br>
Best of luck!<br>
<br>
Matt<br>
<br>
<o:p></o:p></p>
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