Using /126 for IPv6 router links

David Barak thegameiam at
Tue Jan 26 14:38:43 UTC 2010

From: Mark Smith nanog at

>Why can't IPv6 node addressing be as easy to understand and work with
>as Ethernet addresses? They were designed in the early 1980s*. 28 years
>or so years later, it's time for layer 3 addressing to catch up.

Becase Ethernet addresses are only locally significant, are not manually assigned in the vast majority of cases, and changing a MAC by replacing a NIC has no bearing on the configuration of a { server | router ACL | etc }.

Layer 3 addressing is globally significant, and the case we're discussing is addresses which are human-assigned rather than automatically configured.  Link-local autoconfiguration in IPv6 works like a champ, and behaves pretty much the way I would want it to.  Global addressing approaches, on the other hand, are highly optimized in directions which make them less flexible or have surprising consequences (hence this thread).
David Barak
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