IPv6 ranges

David Hankins dhankins at google.com
Thu Jul 7 21:09:38 UTC 2011

On Mon, Jul 4, 2011 at 2:38 PM, Sergiu Bivol <sbivol at bluecatnetworks.com>wrote:

>  The dhcpd.conf man page says that there are 4 ways to declare an IPv6
> range:****
> ** **
> range6 low-address high-address;
> range6 subnet6-number;
> range6 subnet6-number temporary;
> range6 address temporary;****
> ** **
> Questions:****
> - why a range defined with low and high addresses cannot be temporary?

Temporary addresses use a hash function to fill available bit space.  A
low/high number range might not fall on a even bit boundary, so we'd have to
do "weird math" to use addresses in an incomplete bit space.

So this simplifies implementation.

Honestly, no one should ever use the low/high address method unless in
exceptional circumstances, so perhaps it should not be listed in
documentation first.

> ****
> - what is the meaning of the last range6 statement, and when should it be
> used?

I think it assumes a /64 ("by default on 64 bits"), and was the initial
implementation (following the spec which requires a /64 bit space).

David W. Hankins
SRE - Systems Engineer
Google, Inc.
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