IPV6 renumbering painless?

Fri Nov 12 16:19:36 UTC 2004

Daniel Roesen writes:
> On Thu, Nov 11, 2004 at 08:44:57AM -0800, Kevin Oberman wrote:
>> We have renumbered IPv6 space a couple of times when we were
>> developing our addressing plan. (We have a /32.) Renumbering was
>> pretty trivial for most systems, but servers requiring a fixed
>> address were usually configured with an explicit prefix. This
>> should not have been the case, but most people configured IPv6
>> addresses pretty much like IPv4 and specified the entire 128
>> bits. Of course, after a renumbering, this gets fixed, so those
>> systems are usually OK the next time.

> "specified the entire 128 bits"... how do you specify only part of
> it?

On Solaris, you would use the "token" option (see the extract from
"man ifconfig" output below).  You can simply put "token ::1234:5678"
into /etc/hostname6.bge0.  I assume that other sane OSes have similar
mechanisms.

602      token address/prefix_length
603            Set the IPv6 token of an  interface  to  be  used  for
604            address autoconfiguration.
605 
606            example% ifconfig hme0 inet6 token ::1/64
607 

> What determines the rest?

The prefix advertised in prefix advertisements.

> "fixed" as in "now using stateless autoconfig"? Fun... change NIC
> and you need to change DNS. Thanks, but no thanks. Not for
> non-mobile devices which need to be reachable with sessions
> initiated from remote (basically: servers).

The above mechanism solves this problem even with stateless
autoconfiguration.  Agree?

I think it's an advantage if servers can get their prefixes from
router announcements rather than from local config files.  Sure, you
still have to update the DNS at some point(s) during renumbering, but
that can't be avoided anyway.
-- 
Simon.