Subject: Re: [vserver] Re: Linux source address selection vs. EUI-64
From: Udo Burghardt <vserver-ml@udoathome.dyndns.org>
Date: Sun, 14 Nov 2010 09:32:39 +0100

Am 13.11.2010 16:42, schrieb Eugen Leitl:

> On Sat, Nov 13, 2010 at 03:36:57PM +0100, Geert Hendrickx wrote:
>
>> For individual hosts (esp. in a VPS environment), assigning a /64 or
>> larger makes little sense to me, a /96 is more than enough.

> Is that an official recommendation?

The official recommendation is compactly listed on

http://www.ripe.net/info/info-services/addressing.html:
|IPv6 Relative Network Sizes
|/128 1 IPv6 address 	A network interface
|/64  1 IPv6 subnet  	18,446,744,073,709,551,616 IPv6 addresses
|/56  256 LAN segments 	Popular prefix size for one subscriber site
...

A full /64 subnet is necessary to make some automatic mechanisms work as 
specified. This is true for the automatic address configuration (without 
explicit dhcp), the router location service and especially the privacy 
extensions, which will "hide" you in this large address range by using a 
different address for each and every new outgoing connection.

No software expects to find itself in a smaller network as /64. Probably 
some PnP mechanisms like DLNA will also not work work well with smaller 
networks (guessed, not testet). For the most "normal" software this is 
simply unimportant and it will work in any condition.

With a smaller subnet you will lose these capabilities. For this reason 
I do definitely recommend a full /64 for a _workstation_ LAN segment.

For a dedicated server LAN segment (say classic web of email servers in 
a dedicated DMZ) which is often configured manually for its specific 
task and environment this might get ignored.

|I currently have a single /56,
|which I would like to distribute over several thousands customers,
|each on a virtual server,

I would expect this to work with /96 (or even smaller), if those 
vservers can live with the non-presence of the mentioned automatic 
mechanisms but are configured manually.

Actually I did start evaluating IPv6 with an /80. It did successfully 
work the way my 'classic' understanding expected. Due to not-knowing 
about the automatic address assignment rules I didn't realize that I am 
missing some important points.

Best regards
Disclaimer: I am playing with v6 for some time now but _not_ under 
production conditions yet! There might be (more) dragons...

-- 
Udo Burghardt