IPv6 end user addressing

Sun Aug 7 22:44:00 UTC 2011

Jonathon,

On Aug 7, 2011, at 12:09 PM, Jonathon Exley wrote:
> This has probably been said before,

Once or twice :-)

> but it makes me uncomfortable to think of everybody in the world being given /48 subnets by default.

This isn't where the worry should be.  Do the math.  Right now, we're allocating something like 300,000,000 IPv4 addresses per year with a reasonable (handwave) percentage being used as NAT endpoints.  If you cross your eyes sufficiently, that can look a bit like 300,000,000 networks being added per year.  Translate that to IPv6 and /48s:

There are 35,184,372,088,832 /48s in the format specifier currently defined for "global unicast".  For the sake of argument, let's increase the the 'network addition' rate by 3 orders of magnitude to 300,000,000,000 per year.  At that rate, which is equivalent to allocating 42 /48s per person on the planet per year, the current format specifier will last about 100 years. And there are 7 more format specifiers.

> but wouldn't it be wise to apply some conservatism now to allow the IPv6 address space to last for many more years? 

The area to be more conservative is, perhaps unsurprisingly, in the network bureaucratic layer.  I believe current allocation policy states an ISP gets a minimum of a /32 (allowing them to assign 65536 /48s), but "if justified" an ISP can get more.  There have been allocations of all sorts of shorter prefixes, e.g., /19s, /18s, and even (much) shorter.  An ISP that has received a /19 has the ability to allocate half a billion /48s. And of course, there are the same number of /19s, /18s, and even (much) shorter prefixes in IPv6 as there are in IPv4...

> After all, there are only 4 bits of IP version field so the basic packet format won't last forever.

True.  There is no finite resource poor policy making can't make scarce.

Regards,
-drc