https://en.wikipedia.org/wiki/Carrier-grade_NAT
Can anyone elighten me regarding what is different or special about 100.64.0.0/10 vs say, 192.168.0.0 or 10.0.0.0.
Edit: Answered my own question by digging into more wikis, there is a helpful table of reservations and intentions here: https://en.wikipedia.org/wiki/Reserved_IP_addresses
A bit of context: if an ISP cannot get enough IPv4 addresses for the WAN-side of people's home routers, some problems exist:
* something in 192.168/16 is generally used for the LAN-side of people's home routers, so that cannot be used on the WAN side
* 10/8 is used for business/enterprise corporate networks, so it also cannot be used on the WAN side because if people VPN connect to the corporate, then the router may get confused
* similarly for 172.12/12: often used for corporate networks
So the IETF/IANA set aside 100.64.0.0/10 as it had no 'legacy' of use anywhere else, and is specifically called out to only be used for ISPs for CG-NAT purposes. This way its routing does not clash with any other use (home or corporate/business).
IPv4 address space is nearly exhausted. However, ISPs must continue
to support IPv4 growth until IPv6 is fully deployed. To that end,
many ISPs will deploy a Carrier-Grade NAT (CGN) device, such as that
described in [RFC6264]. Because CGNs are used on networks where
public address space is expected, and currently available private
address space causes operational issues when used in this context,
ISPs require a new IPv4 /10 address block. This address block will
be called the "Shared Address Space" and will be used to number the
interfaces that connect CGN devices to Customer Premises Equipment (CPE).