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<p>We performed some high-level analyses on these hyper-specific
prefixes about a year ago and pushed some insights into a blog
post [1] and a paper [2].<br>
<br>
While not many ASes redistribute these prefixes, some accept and
use them for their internal routing (e.g., NTT's IPv4 filtering
policy [3]). Rob already pointed out that this is often sufficient
for many traffic engineering tasks. In the remaining scenarios,
announcing a covering /24 and hyper-specific prefixes may result
in some traffic engineering, even if the predictability of the
routing impact is closer to path prepending than usual
more-specific announcements. In contrast to John's claim, some
transit ASes explicitly enabled redistributions of up to /28s for
their customers upon request (at least, they told us so during
interviews).<br>
<br>
Accepting and globally redistributing all hyper-specifics
increases the routing table size by >100K routes (according to
what route collectors see). There are also about 2-4
de-aggregation events every year in which some origin
(accidentally) leaks some large number of hyper-specifics to its
neighbours for a short time. <br>
<br>
Best regards, <br>
Lars <br>
<br>
[1]
<a class="moz-txt-link-freetext" href="https://blog.apnic.net/2022/09/01/measuring-hyper-specific-prefixes-in-the-wild/">https://blog.apnic.net/2022/09/01/measuring-hyper-specific-prefixes-in-the-wild/</a><br>
[2] <a class="moz-txt-link-freetext" href="https://dl.acm.org/doi/pdf/10.1145/3544912.3544916">https://dl.acm.org/doi/pdf/10.1145/3544912.3544916</a><br>
[3]
<a class="moz-txt-link-freetext" href="https://www.gin.ntt.net/support-center/policies-procedures/routing/">https://www.gin.ntt.net/support-center/policies-procedures/routing/</a><br>
<br>
<br>
</p>
<div class="moz-cite-prefix">On 25.01.23 05:12, Forrest Christian
(List Account) wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAKsZx=0zXQEmziqCDY_uafmfA9+60EYzO+Ua7Rp3yRcO86=WMQ@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="auto">I have two thoughts in relation to this:<br>
<div dir="auto"><br>
</div>
<div dir="auto">1) It's amazing how many threads end up ending
in the (correct) summary that making an even minor global
change to the way the internet works and/or is configured to
enable some potentially useful feature isn't likely to happen.</div>
<div dir="auto"><br>
</div>
<div dir="auto">2) I'd really like to be able to tag a BGP
announcement with "only use this announcement as an absolute
last resort" so I don't have to break my prefixes in half in
those cases where I have a backup path that needs to only be
used as a last resort. (Today each prefix I have to do this
with results in 3 prefixes in the table where one would do).</div>
<div dir="auto"><br>
</div>
<div dir="auto">And yes. I know #2 is precluded from actually
ever happening because of #1. The irony is not lost on me.</div>
<br>
<br>
<div class="gmail_quote" dir="auto">
<div dir="ltr" class="gmail_attr">On Tue, Jan 24, 2023, 7:54
PM John Levine <<a href="mailto:johnl@iecc.com"
moz-do-not-send="true" class="moz-txt-link-freetext">johnl@iecc.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">It appears
that Chris J. Ruschmann <<a
href="mailto:chris@scsalaska.net" target="_blank"
rel="noreferrer" moz-do-not-send="true"
class="moz-txt-link-freetext">chris@scsalaska.net</a>>
said:<br>
>-=-=-=-=-=-<br>
>How do you plan on getting rid of all the filters that
don’t accept anything less than a /24?<br>
><br>
>In all seriousness If I have these, I’d imagine everyone
else does too.<br>
<br>
Right. Since the Internet has no settlements, there is no
way to<br>
persuade a network of whom you are not a customer to accept
your<br>
announcements if they don't want to, and even for the
largest<br>
networks, that is 99% of the other networks in the world. So
no,<br>
they're not going to accept your /25 no matter how deeply
you believe<br>
that they should.<br>
<br>
I'm kind of surprised that we haven't seen pushback against
sloppily<br>
disaggregated announcements. It is my impression that the
route table<br>
would be appreciably smaller if a few networks combined
adjacent a<br>
bunch of /24's into larger blocks.<br>
<br>
R's,<br>
John<br>
</blockquote>
</div>
</div>
</blockquote>
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