Using /126 for IPv6 router links

Richard A Steenbergen ras at
Mon Jan 25 17:07:38 UTC 2010

On Mon, Jan 25, 2010 at 09:10:11AM -0500, TJ wrote:
> While I agree with parts of what you are saying - that using the "simple
> 2^128" math can be misleading, let's be clear on a few things:
> *) 2^61 is still very, very big.  That is the number of IPv6 network
> segments available within 2000::/3.  
> *) An end-user should get something between a /48 and a /56, _maybe_ as low
> as a /60 ... hopefully never a /64.  Really.
> **) Let's call the /48s enterprise assignments, and the /56s home
> assignments ... ?
> **) And your /56 to /64 is NOT 1-256 IPs, it is 1-256 segments.

It is if we are to follow the "always use a /64 as a single IP" 
guidelines. Not that I'm encouraging this, I'm just saying this is what 
we're told to do with the space. I for one have this little protocol 
called DHCP that does IP assignments along with a bunch of other things 
that I need anyways, so I'm more than happy to take a single /64 for 
house as a single lan segment (well, never minding the fact that my 
house has a /48).

> **) And, using the expected /48-/56, the numbers are really 256-64k subnets.
> Note: "All we've really done is buy ourselves an 8 to 16 bit improvement at
> every level of allocation space"
> *) And you don't think 8-16 bits _AT EVERY LEVEL_ is a bit deal??

I'm not saying that 8-16 bits isn't an improvement, but it's a far cry
from the bazillions of numbers everyone makes IPv6 out to be. By the
time you figure in the overhead of autoconfiguration, restrictive
initial deployments, and the "now that the space is much bigger, we
should be reallocating bigger blocks" logic at every layer of
redistribution, that is what you're left with. So far all we've really
done with v6 is created a flashback to the days when every end user
could get a /24 just by asking, every enterprise could get a /16 just by
asking, and every big network could get a /8 just by asking, just bit 
shifted a little bit. That's all well and good, but it isn't a 
bazillion. :)

Richard A Steenbergen <ras at>
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)

More information about the NANOG mailing list