Subject: Fwd: I-D ACTION:draft-ietf-v6ops-vlan-usage-00.txt

From: Fred Baker <[email-masked]>
Date: Wed, 13 Jul 2005 13:03:19 -0700

This passed last call a while ago, and expired immediately afterward. 
The only change I expected in this was that of the name; mostly, it was 
reposting for the IESG's benefit.

If there are any further comments on this draft, please advise.

Begin forwarded message:

> From: [email-masked]
> Date: July 13, 2005 12:50:01 PM PDT
> To: [email-masked]
> Cc: [email-masked]
> Subject: I-D ACTION:draft-ietf-v6ops-vlan-usage-00.txt
>
> A New Internet-Draft is available from the on-line Internet-Drafts 
> directories.
> This draft is a work item of the IPv6 Operations Working Group of the 
> IETF.
>
> 	Title		: Use of VLANs for IPv4-IPv6 Coexistence in Enterprise Networks
> 	Author(s)	: T. Chown
> 	Filename	: draft-ietf-v6ops-vlan-usage-00.txt
> 	Pages		: 12
> 	Date		: 2005-7-13
> 	
>    Ethernet VLANs are quite commonly used in enterprise networks for 
> the
>    purposes of traffic segregation.  This document describes how such
>    VLANs can be readily used to deploy IPv6 networking in an 
> enterprise,
>    which focuses on the scenario of early deployment prior to
>    availability of IPv6-capable switch-router equipment.  In this 
> method
>    IPv6 may be routed in parallel with the existing IPv4 in the
>    enterprise and delivered at Layer 2 via VLAN technology.  The IPv6
>    connectivity to the enterprise may or may not enter the site via the
>    same physical link.
>
> A URL for this Internet-Draft is:
> http://www.ietf.org/internet-drafts/draft-ietf-v6ops-vlan-usage-00.txt
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---

From: Michael H Lambert <[email-masked]>
Date: Thu, 14 Jul 2005 11:38:25 -0400

--On 13 July 2005 13:03:19 -0700 Fred Baker <[email-masked]> wrote:

> This passed last call a while ago, and expired immediately afterward. The
> only change I expected in this was that of the name; mostly, it was

I do have one comment:

----------
2.5  IPv6 Addressing

   One site using this VLAN technique has chosen to number its IPv6
   links with the format [Site IPv6 prefix]:[VLAN ID]::/64.  This is not
   a recommended addressing plan, but some sites may wish to consider
   its usage.
----------

I see two ways of reading this text.  The first is that there is some 
fundamental flaw with this addressing format and other options should be 
considered.  The second is that this format is just being used as an 
example, but the document takes no stand on any particular scheme.

If Tim would please clarify...

Michael

-- 
Michael H. Lambert, Network Engineer           Phone: +1 412 268-4960
Pittsburgh Supercomputing Center               FAX:   +1 412 268-8200
4400 Fifth Avenue, Pittsburgh, PA  15213 USA   [email-masked]

---

From: Gert Doering <[email-masked]>
Date: Mon, 18 Jul 2005 11:09:22 +0200

Hi,

I'assume the second one is what is intended ("this is just an example,
and you can do it this way, but you don't have to"), but indeed the wording
could also be read as "this is NOT RECOMMENDED!  don't do this!".

gert
-- 
Total number of prefixes smaller than registry allocations:  71007  (66629)

SpaceNet AG                    Mail: [email-masked]
Joseph-Dollinger-Bogen 14      Tel : +49-89-32356-0
D- 80807 Muenchen              Fax : +49-89-32356-234

---

From: Stig Venaas <[email-masked]>
Date: Thu, 21 Jul 2005 10:03:13 +0200

> could also be read as "this is NOT RECOMMENDED!  don't do this!".

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. 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.

Stig

---

From: Juergen Schoenwaelder <[email-masked]>
Date: Thu, 21 Jul 2005 11:25:04 +0200

On Thu, Jul 21, 2005 at 10:03:13AM +0200, Stig Venaas wrote:

> 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

---

From: Stig Venaas <[email-masked]>
Date: Thu, 21 Jul 2005 14:00:49 +0200

> hexadecimal letter are kind of preserved and can be used for other 

Right. I do see why this is useful of course. And I agree that it's
more convenient to literally translate them like you say.

> concrete text to add to the document so far. Perhaps this is a start 

I suppose the idea is to make it easy to relate addresses to vlans,
so it definitely seems best to not do any hex conversions. I know
other cases also where people have chosen the "literal" way, simply
because humans need more than a split second to convert between hex
and decimal...

> setup is rather stable. A downside I am more worried about is that using

I understand what you're saying, but I don't find that totally

> installations - but I think this deserves to be mentioned somewhere.

Right, I'm not sure these are worth worrying about though.

> apart into new VLANs in our environment. But even in these cases,

Right, splitting or merging of VLANs should not be a problem. You will
always have to renumber "half" of the hosts.

So the question then is whether any of this should be in the draft.
All of this seems pretty obvious, but if the draft starts suggesting
possible ways of choosing IPv6 prefixes, then it should perhaps add
some pros and cons as you say.

Another comment regarding the draft. The example in the appendix
seems needlessly complex, in particular there is some load
balancing that could be avoided.

Well, as I understand it's been through last call already, it may
not be worth changing the document...

Stig