I think Michael's point is that it can be allocated as "unique space for internal use". i.e. kind of like 1918 space, but you know your slice of 240/4 is only used on your network[1]. For that purpose, it's fine, as long as you determine that all your gear allows it.
Not quite. I don't want to see 240/4 space considered to be like RFC 1918 space in any way shape or form. I just want it available for use between consenting partners which is why I suggest that the RIRs only give it to people who ask for it. Eventually I expect that some ISPs will support this due to customer demand and because it isn't that hard to install the patches required in routers. Anyone who doesn't want to support it need not do anything because the packets will fall on the floor as soon as they hit a router that doesn't support 240/4 addresses. Depending on how the IPv6 transition pans out, there might be a day when 240/4 addressing is widely supported on the Internet. Or there might not. I would just like to see the "reserved" status removed for 240/4 because it is no longer appropriate or necessary.
If anyone really thinks it can be announced into the global routing table and expected to function, I'm afraid they've swallowed the crack pipe so far down that this thread is pointless for them. Too many devices will never (can never[2]) be upgraded and are unlikely to go away in the forseeable future.
Agreed. Routing between consenting networks is not the same as universal routing (if that even exists anymore). Unfortunately, many people do not understand that Internet connectivity is not an all-or-nothing proposition. There are many extranets that function using only a small group of certified ISPs, for instance.
I could see bits of 240/4 perhaps being of use to large cable companies for whom there just isn't enough 1918 space to address all their CPE gear...and/or they really want unique addressing so that if/when networks merge IP conflicts are avoided.
I think that RFC 1918 exhaustion is a separate issue and can only be solved by setting aside another /8 for RFC 1918 space. Either take 125/8 or else see if Softbank Japan is willing to allow 126/8 to be set aside for that purpose.
1) As much as this can ever be known...you can't stop random IP squatters from picking random IP space out of their hats for use as "private" networks behind NAT. Eventually, they realize some bit of the internet is unreachable...because it's their LAN.
Not necessarily. In many cases they only want to reach a subnet of the Internet so they never see the unreachability problem. Or they don't route packets into or out of the public Internet and use split-horizon DNS.
2) Anyone care to guess how much network gear is deployed that either won't or can't be upgraded? i.e. Old cisco gear without the RAM and/or flash to handle a newer code train...the old one in use long since unsupported, or gear from vendors that no longer exist? As long as this stuff generally works, nobody's likely to replace it.
That's why we will see IPv4 in widespread use for at least the next 20 years. --Michael Dillon