Using /126 for IPv6 router links

TJ trejrco at
Mon Jan 25 20:15:55 UTC 2010

> -----Original Message-----
> From: Tim Durack [mailto:tdurack at]
> Sent: Monday, January 25, 2010 14:03
> To: TJ
> Cc: nanog at
> Subject: Re: Using /126 for IPv6 router links


> 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 ISP allocation is /32, which is only 2^16 /48s. Again, not that big.
> Once you start planning a practical address plan, IPv6 isn't as big as
> everybody keeps saying...

I didn't realize "human friendly" was even a nominal design consideration,
especially as different humans have different tolerances for defining
"friendly"  :)

I (continue to) maintain that:
*) 2^16 is still a pretty good size number, even allowing for aggregation /
*) If you are large enough that this isn't true - you should (have)
request(ed) more, naturally - each bit doubles your space ...


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