Using /126 for IPv6 router links

Owen DeLong owen at
Tue Jan 26 01:01:29 UTC 2010

> 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.

> 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.

> 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.


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