IPv6 Addressing Help

William Pitcock nenolod at systeminplace.net
Sat Aug 15 09:29:06 CDT 2009


On Sat, 2009-08-15 at 00:38 -0400, William Herrin wrote:
> With IPv6 we have more than enough addresses to give a /56 to
> everybody who needs more than a /60 and a /48 to everybody who needs
> more than a /56.

I don't think this is a good assumption to make.  Just because the
namespace keylength (where the IP address is the keyvalue) is 96 bits
longer than with IPv4, one needs to keep in mind that there will be
eventually a shortage of addresses, if only theoretical.

> A rapidly escalating assignment series like this would place a strong
> upper bound on the number of routes needed for any one entity
> regardless of how they grow. Allocating from pools reserved solely for
> specific prefix sizes should enable the compression of distant TE
> disaggregation.

I think pooling a /32 or /48 or whatever the allocation is like you
described is however a good idea.  Many of our IPv6 customers however,
only want one specific IP address (so they can IPv6-enable their
website).  We assign those customers /96 subnets, and that seems to be
going pretty well.  The nice benefit of that is that we can aggregate
those as say, a single /64 in our core router without polluting the IGP
routes on our border routers (and IPv6 route entries typically use about
twice as much memory as IPv4 route entries, so that is important to keep
in mind.)

I wish the RFCs had something useful to say about how to handle those
single IP addressing situations.  So far the discussion there is /80
vs /96, but both of those subnets seem wasteful to me.  One of our
upstream providers hands our border router off a /125 (which is just
weird), for these single-ip-needed situations.

William Pitcock        SystemInPlace - Simple Hosting Solutions
1-866-519-6149                    http://www.systeminplace.net/
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