v6 subnet size for DSL & leased line customers

Scott Weeks surfer at mauigateway.com
Thu Dec 20 20:24:27 UTC 2007

--- surfer at mauigateway.com wrote:
I work on a network with 100K+ DSL folks and 200+ leased line customers, plus some other stuff.  The leased line customers are increasing dramatically.  I should plan for a /64 for every DSL customer and a /48 for every leased line customer I expect over the next 5-7 years?

Here's the answer for the other IPv6 wussies, like myself, who don't want to speak up. ;-)  Also, I am using ideas and exact sentances sent to me in private email.  They are not my own, so by saying that I am not plagiarizing you folks who were kind enough to reply to me...  :-)  Last, it is not my intention to start any kind of religious war on the subject.  Only to inform folks that're at my level of IPv6 understanding or below how to get started on planning, so they can then get around to obtaining their block.  Please let me know if my math is wrong.

All subnets (wrong term I'm told, but I'm going to use it anyway) should be a /64 as things like privacy addressing, stateless autoconfiguration and other stuff rely on that being the default subnet size.  This includes my example of a home DSL line.  Households will most likely need more than one subnet as in the future things like wireless gateways might want to create routed topologies, rather than bridging everything into a single subnet.  For example, perhaps I don't want my microwave and refrigerator on the same subnet as my television on the same subnet as my TiVO on the same subnet as my computers.

Once you accept the need for more than one /64 subnet in a household or business, you start looking at a /56 or a /48.  A /56 is 256 /64 subnets and a /48 is 65536 /64s.  At this point you need to know your customer base.  For example, will 256 subnets (a /56) be enough for a business?  In my case, /56s will work, but I will interleave empty blocks in the assigned blocks just in case.  A /32 is 2^24 /56s and is the normally assigned block from ARIN.  This is ~16.8 million /56s, which allows ~8.4 million customers to have 256 /64 subnets each.

My brain numbs at the thought of the numbers we're dealing with...


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