On 12/12/25 15:53, William Herrin via NANOG wrote:
464xlat and similar technologies. Basically, ARIN has a set-aside for
folks who have IPv6 devices on an IPv6 network that have a need to
also talk to IPv4 devices on the Internet via one of the transition
technologies. For that specific use case, there's still a pool of
unallocated addresses available.
In addition to address translation targets, they can (per policy) be
used for other critical functions that require dual-stacking such as DNS
servers (both recursive and authoritative noting that there are still a
lot of "target" networks that are IPv6-enabled but don't have dual-stack
authoritative nameservers) and things like mail servers and potentially
even web servers that require "some rando on the Internet" who may not
have IPv6 at all to be able to hit them.
The (somewhat unwritten) intent appears to be to allow a newly started
entity to still obtain a minimal IPv4 presence so as to facilitate an
"IPv6 first" network deployment without having to wait on the waiting
list or go to the open market via specified transfer. You can get a
4.10 /24 allocation essentially immediately after having an IPv6
allocation provided you use it for the stated purposes.
A /24 is cramped but largely adequate for this purpose for most
newly-started network. If you can justify need for more space such as
because your NAT overload ratio is becoming untenable, you can request
expansion, and ARIN has policies in place to try to make it so that your
expansion space will aggregate with your original space without
requiring you to re-number.
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