IPv6 Subscriber Access Deployments

Wed Sep 9 17:19:49 UTC 2015

Because the designers of IPv6 didn’t want to bake the hardware constraints of equipment available
10+ years ago (20?) into the addressing plan for the future.

Hanging 4k customers off a switch is a current hardware limitation which has almost nothing to do with
IPv6 other than not being possible in IPv4 due to limitations in IPv4 whereas IPv6 does not impose
such limitations in the L3 protocol.

Think of it like consecutive apertures… If you are looking through a pinhole, you can’t see that your
entire view is through the center hole of a washer 1/2” behind the pinhole. (IPv4 is the pinhole in this
case, modern hardware is the washer).

If you open up the pinhole, suddenly the washer becomes visible.

IPv6 is everything beyond the washer visible and obscured.

Owen

> On Sep 8, 2015, at 13:13 , Matthew Kaufman <matthew at matthew.at> wrote:
> 
> If you can't hang 4k customers off a switch, why does IPv6 need so many bits for the host portion?
> 
> Matthew Kaufman
> 
> (Sent from my iPhone)
> 
>> On Sep 8, 2015, at 12:54 PM, Valdis.Kletnieks at vt.edu wrote:
>> 
>> On Tue, 08 Sep 2015 19:40:44 -0000, Josh Moore said:
>> 
>>> The question becomes manageability. Unique VLAN per customer is not always
>>> scalable. For example, only ~4000 VLAN tags. What happens when you have more
>>> than that many customers?
>> 
>> If you're hanging 4K customers off the same switch, you probably have bigger
>> issues than running out of VLAN tags...
>> 
>>> We are talking very, very, small customers here. SOHO to say the most.
>>> /64 should be more than sufficient for their CPE router.
>> 
>> A Linksys WNDR3800 running CeroWRT (and probably OpenWRT by now) will prefer to
>> create multiple /64's - one for the 4 wired ports, one for private access on the
>> 2.4G radio, one for guest access on the 2.4, and another private/guest pair
>> on the 5G radio. So there is CPE gear out there now that can blow through 5 /64s
>> by default, and more if you enable VLANs.
>> 
>> A /56 allocated via DHCPv6-PD would be a *minimum*.  And prefixes are cheap,
>> so you may as well hand them a /48, just in case they have a second WNDR3800
>> at the other end of the building for coverage - because that one will then ask
>> the upstream one for a -PD allocation.  So if you give the CPE a /48, it can
>> keep a /56 for itself, and hand the downstream a /56, and they can each
>> allocate /64s as needed.
>> 
>> And remember - prefixes are cheap and plentiful, so don't bother with /52
>> or /60, just split on 8-bit boundaries to make life easier for yourself...
>> 