One of the immediate benefits of using a /126, is that it's not a /64! Also, a
/126 is the smallest non-64 size with the highest likeliness to get the job
done from an interoperability perspective (not the /127). Another example: when
you use a /120, the advantage again is that it is not a /64, and you can make a
bunch of routers talk BGP with each other on a layer-2 segment. This is why
/126, /125, /124 etc end up being used.
An Addressing Architecture that does not admit this has been common practice
for 15+ years, is disassociated from reality and thus inconsequential and no
good. It does not follow that because you don't see enough advantages, the idea
and practice are bad.
Kind regards,
Job
On 22 Feb 2017, 04:52 +0100, Lorenzo Colitti <lorenzo(_at_)google(_dot_)com>,
wrote:
On Wed, Feb 22, 2017 at 12:12 PM, Christopher Morrow
<christopher(_dot_)morrow(_at_)gmail(_dot_)com
(mailto:christopher(_dot_)morrow(_at_)gmail(_dot_)com)> wrote:
But the configuration cost and management overhead is not proportional to
the hosts that are served by those interconnections, it is proportional
to the number of interconnections. A 10x100G peering interconnection that
serves X million hosts is one interface that has to be managed.
isn't the dicsussion here really:
"If you want to use /64 go ahead, if you want to use /121 go for it, if you
want to use SLAAC you'll get a /64 and like it"
Not sure. I for one wouldn't agree with that position, because I don't see
that /121 has enough advantages over /127 and /64 - and few enough downsides
for general-purpose hosts - to make it a good idea in general.