IPv6: numbering of point-to-point-links

bmanning at vacation.karoshi.com bmanning at vacation.karoshi.com
Mon Jan 24 07:18:20 CST 2011


On Mon, Jan 24, 2011 at 02:10:48PM +0100, Marco Hogewoning wrote:
> > While reading up on IPv6, I've seen numerous places that subnets are now
> > all /64.
> > 
> > I have even read that subnets defined as /127 are considered harmful.
> 
> RFC3627, with a lot of discussion in the IETF on this. See also https://datatracker.ietf.org/doc/draft-ietf-6man-prefixlen-p2p/
> 
> > However while implementing IPv6 in our network, I've encountered several
> > of our peering partners using /127 or /126 for point-to-point links.
> 
> I personally don't any benefit in using /126 subnets.
> 
> > What is the Best Current Practice for this - if there is any?
> > 
> > Would you recommend me to use /64, /126 or /127? 
> > 
> > What are the pros and cons?
> 
> >From an operational point of view there is a risk that be using /64 somebody can eat away a lot of memory by either scanning or even changing addresses. This is also described in the draft above...
> 
> I would personally recommend to at least always assign the /64, even if you would decide to configure the /127. RFC 3627 has been around long enough that you will keep running into equipment or software that won't like the /127. In which case you can always revert back to /64.
> This will also allow you to use easy to remember addresses like ::1 and ::2, saving you the headache of a lot of binary counting.
> 
> Grtx,
> 
> Marco

this results in -very- sparse matrix allocation - which is fine, as long as you believe that 
you'll never run out/make mistakes.  personally, i've use /126 for the past 12 years w/o any
problems.

there was never supposed to be a hard split at /64 - it was done as a means to simplify autoconfig.

--bill




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