v6 subnet size for DSL & leased line customers

Deepak Jain deepak at ai.net
Fri Dec 21 18:33:15 UTC 2007

> Given that a "subnet" in the current model consists of a network that is
> capable of swallowing the entire v4 Internet, and still being virtually
> empty, it should be clear that *number of devices* will never be a serious
> issue for any network, business or residential.  You'll always be able to
> get as many devices as you'd like connected to the Internet with v6.  This
> may ignore some /current/ practical issues that devices such as switches
> may impose, but that doesn't make it any less true.

This is the part about V6 I haven't really gotten my head around. It 
really seems like it takes the position (possibly due to WG-delay) that 
everything we've learned to do with V4 is done and not-needed.

For example... Within one's own network (or subnet if you will) we can 
absorb all the concepts of V4 today and have lots of space available. 
For example... for the DMZ of a business... Why not give them 6 bits 
(/122?) are we anticipating topology differences UPSTREAM from the 
customers that can take advantage of subnet differences between /64 and 
/56 ?

Do we really believe that in our "home" topology where everything has a 
unique address that my refrigerator won't be able to route to my movie 
player? And if it can, and if I need a firewall between my in-home 
networks why does it need to be at /64 boundaries... can I subnet my /64 
into a huge number of /116s? I know some IPV6 boxen won't support DHCP 
and other things at such small network sizes, but I haven't figured out 
a use for as much space as we are providing even joe-home-user.... or 
why there is some nobility to making boxes that are less flexible that 
the IPv4 boxen we have today...  between the /48 and /128 boundaries 
(inclusive)... shouldn't IPv6 be just IPv4 with more space?

My previous understanding was the idea that everyone would get an IP4 
universe (or several) to theoretically number everything they could ever 
conceive of, AND have enough left over to handle things like thousands 
of interfaces with thousands of simultaneous permanent and 
semi-permanent conversations going on --even separated by large TTLs (> 
years) without any concern for numbering/renumbering within their 
assigned block. I am aware of the idea of renumbering the left portion 
of the IP space in an IPv6 world...

For example... My car manufacturer could give every car in his universe 
a unique IP within a network. As an owner of that car, I just need to 
create a tunnel from my IP space provided by my provider to my car's 
unique IP (the manufacturer's network won't accept packets for my car 
NOT from my IP space). So now I can create a webpage from my home that 
shows all the silly things I do with my car... and its unique and 
permanent to the rest of the world -- even as I change cars. When I'm 
"on-the-job" as a physical package courier, my car might even gain 
another IP with another access model tunneled over to it.

So, I can see a place where LOTS of devices have LOTS of addresses all 
in different contexts/topologies based on your access model. What I 
don't understand is why an end user connection today that justifies a 
/30 needs a /64.. or multiple ones. What at the ISP changes between a 
/30 and a /56 that we are going to do for that user to support his 
"multiple random networks of convenience?"

Thanks for any help with my understanding,


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