Linux source address selection vs. EUI-64

Frank Bulk frnkblk at
Sat Nov 13 20:35:48 CET 2010

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
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

For all the customers in a virtual environment to share one /64 and then use
a /96 out of it for their own address space suggests that the hosting
provider is still thinking in IPv4 terms.

These providers all give a /64 per customer:


-----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

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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