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

Fernando Gont fernando at
Wed Jan 26 22:09:43 CST 2011

On 26/01/2011 06:14 a.m., Owen DeLong wrote:
>>> That said.  Any size prefix will likely work and is even permitted by
>>> the RFC.  You do run the risk of encountering applications that assume
>>> a 64-bit prefix length, though.  And you're often crippling the
>>> advantages of IPv6.
>> Just curious: What are the advantages you're referring to?
> 1.	Sparse addressing

This comes at a cost, though.

> 2.	SLAAC
> 3.	RFC 4193 Privacy Addressing

Privacy Extensions "solve" (*) a privacy issue *introduced* by SLAAC
embedding the MAC addresses in the IID. -- So, if anything, I deem this
as a patch, rather than a feature.

(*) there is some bibliography about the effectiveness of privacy
addresses. Some have even argued that they are harmful.

> 4.	Never have to worry about "growing" a subnet to hold new machines.

As in #1, this comes at a price.

> 5.	Universal subnet size, no surprises, no operator confusion, no bitmath.

With quite a bit of experience with subnetting (from IPv4), I doubt this
can be flagged as a benefit.

Fernando Gont
e-mail: fernando at || fgont at
PGP Fingerprint: 7809 84F5 322E 45C7 F1C9 3945 96EE A9EF D076 FFF1

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