Linux source address selection vs. EUI-64

Eugen Leitl eugen at
Sat Nov 13 21:34:04 CET 2010

On Sat, Nov 13, 2010 at 01:35:48PM -0600, Frank Bulk wrote:

> If in the physical world a network administrator would assign a /64 per
> network segment (the prefix shouldn't be longer) for one or more servers or

In this case I have been assigned a /56, for a rack or two. 
Assuming two or three (or four) networks for a server, I see
no shortages of assigning a /64 to each individual server NIC.
As each invidiual server will typically run hundreds of virtual
hosts (I currently fill an IPv4 /24 from a single dual-core Atom), 
each virtual guest (individual small customer) would get a /96.

> workstations in a broadcast domain, then it should hold that each customer
> in a virtual environment should have at least a /64, no smaller, for 1 to n
> servers.  

The virtual server guests are extremely lightweight. They even do not
have an individual MAC. What I'm asking is a genuine need for
such a minimal slice of a virtual estate (not even blessed with
an own MAC) for a whole /64. Do arguments like
for such deployments hold water?

> For all the customers in a virtual environment to share one /64 and then use

No, one customer (at least) one virtual server, each with a /96. 
One physical server, one /64 for each NIC.

> a /96 out of it for their own address space suggests that the hosting
> provider is still thinking in IPv4 terms.

I did actually ask for a /48, but have gotten only a /56.
I was thought my provider miserly, but in retrospect the
assignment makes a lot more sense. 
> These providers all give a /64 per customer:

The arguments in above
seem to indicate that's too lavish, and we will see IPv6
exhaustion within our lifetimes. (I agree, though mostly
for other, more lunatic reasons).
> Frank
> -----Original Message-----
> From: at
> [ at] On Behalf Of
> Eugen Leitl
> Sent: Saturday, November 13, 2010 9:32 AM
> To: ipv6-ops at
> Subject: Re: Linux source address selection vs. EUI-64
> 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? I currently have a single /56,
> which I would like to distribute over several thousands customers,
> each on a virtual server, with currently one static IPv4 address.
> I can see how a /96 for each customer would be more than enough
> (especially that since hundreds of customers are going to share
> the same MAC, due to the low-overhead virtualization technology
> used). 
> Presumably, in above context it would be a sane thing to parcel 
> the /56 into /64, each for one physical server's distinct NIC 
> MAC, and from each /64 a /96 for each virtual server?
> -- 
> Eugen* Leitl <a href="">leitl</a>
> ______________________________________________________________
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Eugen* Leitl <a href="">leitl</a>
ICBM: 48.07100, 11.36820
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