Re: [vserver] Re: Linux source address selection vs. EUI-64

From: Udo Burghardt <vserver-ml_at_udoathome.dyndns.org>
Date: Sun 14 Nov 2010 - 08:32:39 GMT
Message-ID: <4CDF9EA7.1020806@udoathome.dyndns.org>

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
Received on Sun Nov 14 08:33:18 2010
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