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Re: Fwd: I-D ACTION:draft-ietf-v6ops-vlan-usage-00.txt
On Thu, Jul 21, 2005 at 10:03:13AM +0200, Stig Venaas wrote:
> I also think the second is the intention. However, I think it might be a
> bad idea, so I would perhaps prefer to read it as "don't do this". When
> picking IPv6 prefixes for links people use all kinds of creative tricks
> where the prefixes have some meaning. This is one example. I understand
> it can make it easier for some administrator initially.
I have recently adopted this scheme and so far this has proven to be
a nice idea although we had a discussion whether we translate VLAN
numbers into equivalent hexadecimal numbers or whether we literally
translate the numbers. We decided to literally translate the numbers,
that is VLAN 1234 becomes IPv6 prefix <PREFIX>.1234 since the goal of
this scheme is to make things really easy for administrators. (A nice
benefit of this approach is also that all prefixes with at least one
hexadecimal letter are kind of preserved and can be used for other
purposes later on.)
Anyway, what I really would have liked to see is a discussion what the
pros and cons are and for example whether you translate numbers
literally or the real numbers. This would have added practical value
to the document. (But I do not complain since I myself did not submit
concrete text to add to the document so far. Perhaps this is a start
now.)
The argument that "once you decide on a scheme you might later regret it
if you have to change the scheme" is not totally convincing. I believe
this scheme has operationally clear advantages, especially if your VLAN
setup is rather stable. A downside I am more worried about is that using
the literal mapping scheme reduces the practically used IPv6 address
space and makes it a bit more feasible to heuristically search IPv6
address spaces. Not sure how much this is a real issue in practical
installations - but I think this deserves to be mentioned somewhere.
> Problem is that you may later be forced to renumber just to preserve
> your naming, or you don't and then you have exceptions to the rule
> that was initially created.
Sure, this is a point to add. The scheme requires to be consistent. If
you change your VLAN numbers without changing the IPv6 prefixes, you
loose all the benefits and the scheme turns very quickly against you.
So yes, this should be spelled out and people adopting the scheme
should be prepared to do such renumberings. We are clearly prepared
to do just that in case VLANs will be renumbered (something I hardly
imagine to happen - it is usually more likely that VLANs are split
apart into new VLANs in our environment. But even in these cases,
we prefer to renumber the IPv6 clouds as well for consistency.
/js
--
Juergen Schoenwaelder International University Bremen
<http://www.eecs.iu-bremen.de/> P.O. Box 750 561, 28725 Bremen, Germany