v6 subnet size for DSL & leased line customers

Owen DeLong owen at delong.com
Fri Dec 21 16:31:07 UTC 2007

> The primary reasons I see for separate networks on v6 would include
> firewall policy (DMZ, separate departmental networks, etc)...
This is certainly one reason for such things.

> And I'm having some trouble envisioning a residential end user that
> honestly has a need for 256 networks with sufficiently differently
> policies.  Or that a firewall device can't reasonably deal with those
> policies even on a single network, since you mainly need to protect
> devices from external access.
Perhaps this is a lack of imagination.

Imagine that your ethernet->bluetooth gateway wants to treat the  
and ethernet segments as separate routed segments.

Now, imagine that some of your bluetooth connected devices have reasons
to have some topology behind them... For example, you have a master
appliance control center which connects via Bluetooth to your network,
but, uses a different household control bus network to talk to various
appliances.  For security reasons, you've decided not to have your
kitchen appliances be able to talk to your media devices (Who wants
a virus in some downloaded movie to be able to change the temperature
in your refrigerator?).

> I keep coming to the conclusion that an end-user can be made to work  
> on
> a /64, even though a /56 is probably a better choice.  I can't find  
> the
> rationale from the end-user's side to allocate a /48.  I can maybe see
> it if you want to justify it from the provider's side, the cost of  
> dealing
> with multiple prefix sizes.
I can easily envision the need for more than a /64 in the average home
within short order. If nothing else, the average home will probably
want to be able to accommodate:
	Guest network
	Home wired network
	Wireless network(s)
	Bluetooth segment(s)
	Media network
	Appliance Control netowrk
	Lighting Control network

However, I agree that in any vision I can come up with today, the need
for more than 256 is beyond my current imagination.

I think it makes sense to assign as follows:

/64 for the average current home user.
/56 for any home user that wants more than one subnet
/48 for any home user that can show need.


More information about the NANOG mailing list