Using IPv6 with prefixes shorter than a /64 on a LAN

Florian Weimer fweimer at
Thu Feb 3 07:03:36 CST 2011

* Ray Soucy:

> Every time I see this question it' usually related to a fundamental
> misunderstanding of IPv6 and the attempt to apply v4 logic to v6.

True, you have to ignore more than a decade of IPv4 protocol
development and resort to things like pre-VLSM networking.

> That said.  Any size prefix will likely work and is even permitted by
> the RFC.

Could you quote chapter and verse, please?  RFC 4291 section 2.5.4
says this:

   All Global Unicast addresses other than those that start with binary
   000 have a 64-bit interface ID field (i.e., n + m = 64), formatted as
   described in Section 2.5.1.

Florian Weimer                <fweimer at>
BFK edv-consulting GmbH
Kriegsstraße 100              tel: +49-721-96201-1
D-76133 Karlsruhe             fax: +49-721-96201-99

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