Using /126 for IPv6 router links

Tim Durack tdurack at
Tue Jan 26 15:27:35 UTC 2010

On Mon, Jan 25, 2010 at 6:20 PM, Nathan Ward <nanog at> wrote:
> Why do you force POP infrastructure to be a /48? That allows you only 16 POPs which is pretty restrictive IMO.
> Why not simply take say 4 /48s and sparsely allocate /56s to each POP and then grow the /56s if you require more networks at each POP.
> You only have a need for 4 /64s at each POP right now, so the 256 that a /56 gives you sounds like more than enough, and up to 1024 POPs (assuming you don't outgrow any of the /56s).

NRPM says: Assignment to operator's infrastructure
An organization (ISP/LIR) may assign a /48 per PoP as the service
infrastructure of an IPv6 service operator. Each assignment to a PoP
is regarded as one assignment regardless of the number of users using
the PoP. A separate assignment can be obtained for the in-house
operations of the operator.

Currently living with mixed infrastructure/customer address space, so
I'm quite happy to separate this out. We will also have a /48 per-pop
for service we provide, such as DHCP/DNS/Web etc. Essentially we will
be a customer of our own infrastructure. I believe the above wording
allows for that.

> Also I'd strongly recommend not stuffing decimal numbers in to a hexadecimal field. It might seem like a good idea right now to make the learning curve easier, but it's going to make stuff annoying long term. You don't have anything in IPv4 that's big enough to indicate the VLAN number and you've lived just fine for years, so forcing it to be decimal like that isn't really needed.
> You're much better off giving your staff the tools to translate between the two, rather than burn networks in order to fudge some kind of human readability out of it and sacrificing your address space to get it.
> % printf "%04x\n" 4095
> 0fff
> % printf "%d\n" 0x0fff
> 4095
> --
> Nathan Ward

Maybe so. Right now we convert VLAN IDs to IPv4 3rd octet. Every
access switch gets a dedicated set of VLANs along these lines:

48, 348, 648, 1048 etc.

That leaves space for 128 access switches per POP, without having to
think about anything. The not having to think part is significant, as
it trades human engineering for address space. That is also one of our
goals for IPv6 deployment.


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