Using /126 for IPv6 router links

Tim Durack tdurack at
Tue Jan 26 02:26:13 UTC 2010

On Mon, Jan 25, 2010 at 8:01 PM, Owen DeLong <owen at> wrote:
> 2^128 is a "very big number." However, from a network engineering
> perspective, IPv6 is really only 64bits of network address space. 2^64
> is still a "very big number."
> An end-user assignment /48 is really only 2^16 networks. That's not
> very big once you start planning a human-friendly repeatable number
> plan.
> An end-user MINIMUM assignment (assignment for a single "site") is
> a /48.  (with the possible exception of /56s for residential customers
> that don't ask for a /48).
> I have worked in lots of different enterprises and have yet to see one that
> had more than 65,536 networks in a single site.  I'm not saying they don't
> exist, but, I will say that they are extremely rare.  Multiple sites are a
> different
> issue.  There are still enough /48s to issue one per site.

Networks per site isn't the issue. /48s per organization is my
concern. Guidelines on assignment size for end-user sites aren't
clear. It comes down to the discretion of ARIN. That's why I like pp
106. It takes some of the guess-work/fudge-factor out of assignments.

> An ISP allocation is /32, which is only 2^16 /48s. Again, not that big.
> That's just the starting minimum.  Many ISPs have already gotten much larger
> IPv6 allocations.

Understood. Again, the problem for me is medium/large end-user sites
that have to justify an assignment to a RIR that doesn't have clear
guidelines on multiple /48s.

> Once you start planning a practical address plan, IPv6 isn't as big as
> everybody keeps saying...
> It's more than big enough for any deployment I've seen so far with plenty
> of room to spare.
> Owen

Sent from Brooklyn, NY, United States

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