
Visibility of IPv4 and IPv6 Prefix Lengths in 2019 - pjf
https://labs.ripe.net/Members/stephen_strowes/visibility-of-prefix-lengths-in-ipv4-and-ipv6
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zamadatix
I find it curious their IPv4 table from 2019 shows a ton of /30s appeared
since 2011, is there any reason to use a /30 instead of a /31?

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fusl
As far as my understanding goes, RFC3021 is unsupported on some router devices
widely used as it doesn't have a broadcast and network address and is
therefore invalid (/s), so some ISPs default to /30 instead for peering and
don't filter out their peering networks in BGP.

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kbirkeland
I think the reason for using /30s instead of /31s is mostly legacy. It's a 19
year old standard and most vendors support it.

Regardless of the point-to-point subnet used for the local peering connection,
it's interesting that that many /30s have leaked into the default-free zone.
BCP 194 recommends filtering IPv4 prefixes longer than a /24.

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ggm
I'm told the V6 /48 include ddos mitigation defensive routing. Many of them
have a covering /32

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kbirkeland
Advertising the longest generally-accepted prefix is more of a BGP hijack
defense than a DDoS defense. Longest prefix always wins in IP forwarding, so
advertising the longest prefix enforces that the best path to you is (usually)
selected by local preference or AS path length.

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dylz
I see it used in DDoS defense by "hijacking" the traffic of the /32\. The
standard unprotected provider gets hit and the mitigation provider announces a
more specific /48 then tunnels the traffic back out of band

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GrumpyNl
Where are the horror stories, that we needed IPV6 because in one year we will
be running out of ipv4. Thats over 5 years ago.

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the8472
The lack of end-to-end reachability makes it harder to build decentralized
applications, thus adding more fuel to centralization.

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wbl
What lack? Use IPv6.

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the8472
I do, but it's not ubiquitous yet. Many people are behind IPv4-only CGNAT.

