Private use of non-RFC1918 IP space (IPv6-MW)

Nathan Ward nanog at
Thu Feb 5 03:19:54 UTC 2009

On 5/02/2009, at 3:09 PM, Matthew Moyle-Croft wrote:

> TJ wrote:
>> No, we should hand each home a /56 (or perhaps a /48, for the  
>> purists out
>> there) - allowing for multiple segments (aka subnet, aka links,  
>> etc.).
> If there are, say, 250-500 million broadband services in the world  
> (probably more) then, if every ISP followed best practise for IPv6  
> address allocation, (sparse, bits for infrastructure, whatever etc)  
> then what percentage of the space do we have left if we hand out /56  
> or /48s?).  Taking into account the space already carved off for  
> link local, private addressing, US Military etc.
> Has anyone done some analysis of what this might look like?   
> Especially with growth etc.

My addressing plan works like this:

ISP gets /32, 2001:db8::/32
- 2001:db8:0::/48 = ISP use
-- 2001:db8:0:0::/64 = infrastructure
--- 2001:db8:0:0:0:0:0::/112 = loopbacks ( 65536 )
--- 2001:db8:0:0:1:0:0::/112 through 2001:db8::ffff:ffff:ffff:0/112 = / 
112 link nets between ISP routers  ( 281474976710656 )
-- 2001:db8:0::/64 through 2001:db8:0:ffff::/64 = ISP networks, ie.  
servers, etc.
- 2001:db8:1::/64 through 2001:db8:ffff:ffff::/64 = customer networks.

Assuming the above, we have 65535 /48s available to customers, or  
16,711,680 /56s.

The "ISP use" /48 burns 256 /56s, or potential customers. So, like  
burning a /24 for the entire ISP operation.

So, if you have more than 65K business customers, get more than a /32.
If you have more than 16M residential or small business customers, get  
more than /32.

The above plan puts the addresses you type lots (loopbacks, link nets)  
on the shortest addresses you have - you can use the zero  
compression :: thing. These are also the addresses that cause the most  
trouble if fat fingered, so shorter addresses leave less room for error.
In addition, the entire first /64 (loopbacks, link nets) should never  
really receive packets from outside the network. Drop in an ACL.

Modification to the above plan is to use /64s for link nets between  
ISP routers, if you are worried about compatibility issues. You now  
have a trade off between 65k ISP server networks, and 65k link nets.  
Let's say 32k for each.

Nathan Ward

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