I have a question to the authors and ISPs as well, which may help explain why using RFC 1918 and Class-E address space can't be done; or it may not if the answer is different. The question: could this new address space be used *without* a NATing CPE being provided by the ISP? In other words, could an ISP using CGNs deploy this new address space such that the address is used all the way to the consumer's interface, and the consumer can either buy a home NAT box or even not do so? An example would be a 3GPP/LTE provider could use this space all the way to the mobile-phone/laptop-3G-card, or a broadband cable/DSL provider could use this space through their cable-modem/DSL-modem and the customer in the home would get one or more addresses from the space in DHCP (and they could buy a home NAT or not do so). It seems to me that is possible - cable-modems/dsl-modems today don't normally NAT afaik, and there's no consumer CPE in-between in 3GPP/LTE cases. (and 3GPP/LTE is where most of the address growth is) If that's a legit use-case, then no RFC 1918 address space nor 240/Class-E space could possibly be used. The reason for that is the address goes to a device the ISP is not in control of, and cannot reasonably mandate changes to. ISPs can't mandate all consumer NATs purchased in retail stores change overnight, nor can they mandate all consumers use home NATs, nor can they expect all consumer laptops/3g-phones change. For RFC 1918 space, the problem with picking it isn't so much that the ISP can't pick one that consumer NATs don't use - it's that they can't pick one that no Enterprise on a *different* ISP uses. For example, assume my employer used 10.64.0.0/10 (they probably do somewhere), and connected to ISP-A. I connect to ISP-B using a 3GPP laptop-card, and get the same 10.64.0.0/10 address space. I now cannot use a VPN to my employer, because of the resulting conflict in the routing table in my laptop. But there's nothing I nor my *ISP-B* can do about this, because my employer has been using that address for a long time (legitimately) and is connected to *ISP-A*. -hadriel _______________________________________________ Ietf mailing list Ietf@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf