Also, as for /48 vs. /56 etc, etc, this ground has been covered many times. Basically, /48s are what the IANA recommends to assign to end users with more than one LAN, or businesses, per site. It might seem wasteful, but the IPv6 space is so huge that it's not a concern.
It has been covered many times, and the obviously wrong answer reached and stubbornly defended every time. A /56 is ludicrous overkill. A /48 is just throwing bits away for no reason at all. A /48 for every user (which, in virtually every case, will be populated by a single device) means that essentially all of the addressing of the internet must be crammed into 48 bits. That's only slightly longer than an IPv4 address.
A middle-ground projection of future world population is 15 billion. Dividing by the current population of internet-enabled users, we see that growth by a factor of 32 (5 bits) is reasonable to expect. Allocating larger prefixes higher up in the network hierarchy genuinely might help with routing (though I don't see how allocating extra bits at the level of a customer's home network does that), so we can expect to lose,
very conservatively, another factor of 64 (6 bits) for that. Internet growth is exponential even in regions where most of the population already has internet access (due to the proliferation of new ways and places that an individual accesses the internet throughout his day, i.e. all of the new mobile devices now coming on the market). We can expect at least a factor of 16 (4 bits) from that. There's a factor of 8 taken out by the IANA because of the reservation of most of the /3's. Putting it all together:
+ 32 bits currently occupied by the world
+ 5 bits population growth and internet uptake
+ 6 bits elbow room for routing
+ 4 bits device proliferation
+ 3 bits reserved by IANA
----
50 bits needed
And yet we're giving each residential home user a /48? And you don't think it's a concern? And this only takes into account likely, known scenarios. What about the unknown unknowns? Shouldn't we plan for that? What if we want to assign IP address space to other astronomical bodies or something (sure, there's lag, but that's not a huge problem for streaming multimedia).
Having large assignments like that also reduces the size of routing tables and makes routing faster/less expensive (less expensive TCAM needed, etc).
Why does allocating a bigger prefix make routing more efficient
even when the extra bits will obviously not be used by the customer? Name a case where an ordinary user will need
thousands of
subnets. Even a futuristic sci-fi case. I can't think of one.
So I would want a /48 if I had, for example, more than about 500 hosts on my LAN?
Nope. One subnet is always a /64. You would need a /48 if you had about 500 subnets, each with multiple computers and a router of its own. If you only have a hundred or so subnets, not thousands, a /56 is fine. In reality, no one has more than one subnet at home, so a /64 is fine. If some weirdo really wants multiple subnets at home, they should request special treatment from their provider and expect to pay more. /56 by default is silly and /48 is indefensible.
In the year 3000, there will not be one single IP address in the world with any nonzero bits between the 48th and 56th bit (I invite you to try and argue otherwise), but the address space above that will be crammed and crowded as all heck. There's something wrong with that.
Author
Topic: routed /48 (Read 14585 times)