Subject: [dhcwg] Whether DHCPv6 could support assigning an IPv6 prefix and an IPv4 address simultaneously?

From: liu dapeng <[email-masked]>
Date: Wed, 15 Jul 2009 15:56:54 +0800

Hi,guys,
  I have a question about whether current DHCPv6 specification could
support assigning an IPv6 prefix and an IPv4 address simultaneously?

BR,
Dapeng Liu

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From: "Bernie Volz (volz)" <[email-masked]>
Date: Wed, 15 Jul 2009 07:02:46 -0400

Did you really mean IPv4 address?

DHCPv6 only handles IPv6 prefixes and addresses, not IPv4. DHCPv4 is
used for IPv4.

This was discussed when DHCPv6 was being developed, but there was little
practical value to complicating DHCPv6 with supporting IPv4 as well --
after all DHCPv4 was already widely deployed and in use.

Other than saving the 4 messages (2 if rapid commit is used) for a
separate DHCPv4 exchange, why do you see this as being valuable?

- Bernie

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of liu dapeng
Sent: Wednesday, July 15, 2009 3:57 AM
To: [email-masked]
Subject: [dhcwg] Whether DHCPv6 could support assigning an IPv6 prefix
andan IPv4 address simultaneously?

Hi,guys,

BR,
Dapeng Liu
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From: Tim Chown <[email-masked]>
Date: Wed, 15 Jul 2009 12:21:21 +0100

A number of the issues with this, and pros/cons of separate DHCv4/v6
services compared to DHCPv6 serving v4 data were discussed in RFC4477.

http://www.ietf.org/rfc/rfc4477.txt

This explains why the separate server appraoch was preferred (well,
both services could be run from one entity of course, and it would
be prudent to consider managing them consistently and even via a
combined interface).

If that's worth revisiting from 3 years of operational experience, 
any input would be welcome.

Tim

-- 
Tim

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From: Behcet Sarikaya <[email-masked]>
Date: Wed, 15 Jul 2009 09:01:33 -0700 (PDT)

Hi Dapeng,
  My answer would be yes.
Please take a look at http://tools.ietf.org/html/draft-ietf-mip6-hiopt-17
this draft which is in RFC Editor queue defines DHCPv6 options to carry IPv4 address.

Vice-versa is also possible, please look at http://tools.ietf.org/id/draft-xia-mext-hioptv4-00.txt where we defined DHCPv4 option to carry IPv6 address.

Regards,

Behcet

----- Original Message ----
> From: liu dapeng <[email-masked]>
> To: [email-masked]
> Sent: Wednesday, July 15, 2009 2:56:54 AM
> Subject: [dhcwg] Whether DHCPv6 could support assigning an IPv6 prefix and an IPv4 address simultaneously?
> 
> Hi,guys,

---

From: liu dapeng <[email-masked]>
Date: Thu, 16 Jul 2009 00:13:11 +0800

Thanks Tim, please see inline

> any input would be welcome.

We are exploring an host based IPv4/IPv6 transition mechanism named
PNAT and  we are considering to use DHCPv6 to assign an IPv6 prefix
and an IPv4 address for the host at the same time to facilitate PNAT.
http://www.ietf.org/mail-archive/web/behave/current/msg06206.html

Maybe I could post a draft about the required extention of DHCPv6 and
use it for our discussion.

BR,
Dapeng Liu

---

From: "David W. Hankins" <[email-masked]>
Date: Wed, 15 Jul 2009 09:45:57 -0700

> separate DHCPv4 exchange, why do you see this as being valuable?

For awhile I toyed with the idea because DHCPv6's unconfigured
communications model is superior (and because of it, we don't have
worries like non-implementation of udp fragmentation and so forth).

It seems like a complication because this creates now two IPv4
configuration sources and we're already in bad enough shape in
this regard; two IPv6 sources of configuration (RA and DHCPv6), and
two sources of IP-nonspecific configuration state (DHCPv4 and DHCPv6).

The dependency graph is plenty bad enough.

But the final model after an IPv4-capable-DHCPv6 is well deployed
would be for one source of configuration (DHCPv6 only), a net
simplification, and a schedule to retire DHCPv4 without relying on
retiring IPv4 first (or ever).

-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins

---

From: liu dapeng <[email-masked]>
Date: Thu, 16 Jul 2009 00:28:15 +0800

Hi, Behcet,
   Thank you for your information. But it seems that the extentions
could only be used for MIP6/DSMIP home information discovery. We are
looking for an extention which can be used for PNAT (you can refer my
reply to Tim).

BR,
Dapeng Liu

2009/7/16, Behcet Sarikaya <[email-masked]>:
> Vice-versa is also possible, please look at
> http://tools.ietf.org/id/draft-xia-mext-hioptv4-00.txt where we defined
> DHCPv4 option to carry IPv6 address.
>
> Regards,
>
> Behcet
>
>
>

---

From: Ted Lemon <[email-masked]>
Date: Wed, 15 Jul 2009 11:48:34 -0500

> and an IPv4 address for the host at the same time to facilitate PNAT.

My question about this is, why not just use DHCPv4 to get the IPv4  
address?

---

From: Hui Deng <[email-masked]>
Date: Mon, 20 Jul 2009 23:26:46 +0800

the scenario is about a dual stack host but only IPv6 access network
is available.

-Hui

---

From: Hui Deng <[email-masked]>
Date: Mon, 20 Jul 2009 23:29:56 +0800

Haven't this draft got sufficient review from DHCWG since RFC 4477 is
already there?

-Hui

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From: Hui Deng <[email-masked]>
Date: Mon, 20 Jul 2009 23:36:12 +0800

> retiring IPv4 first (or ever).
==> I agree, this is what we think and then proposed in behave working group.

-Hui

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From: Ted Lemon <[email-masked]>
Date: Tue, 21 Jul 2009 04:54:28 -0700

On the other hand, once IPv6 is deployed, you won't need IPv4 at all anymore, and so having IPv4 options in DHCPv6 would be inappropriate when looked at from that perspective.

More to the point, IPv4-capable devices already know how to get IPv4 addresses, so defining a new mechanism for configuring them with IPv4 addresses is likely to create confusion and interoperability problems.

So I persist in asking: why do you prefer to do this in DHCPv6?   If your only reason is that it makes the protocol look neater in the long run, I think that reason is (a) not correct, and (b) not a good reason.

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From: liu dapeng <[email-masked]>
Date: Tue, 21 Jul 2009 21:08:06 +0800

> My question about this is, why not just use DHCPv4 to get the IPv4

The scenario in PNAT is that the host only has IPv6 connectivity, so
can not use DHCPv4.

The IPv4 address and IPv6 prefix is used for synthesizeing an IPv6
address used for the IPv6 host as its IPv6 address.

---

From: liu dapeng <[email-masked]>
Date: Tue, 21 Jul 2009 21:46:41 +0800

> Did you really mean IPv4 address?

Yes.  The IPv4 address is used for synthesizeing an IPv6 address
together with the IPv6 prefix in PNAT scenario.

> after all DHCPv4 was already widely deployed and in use.

DHCPv4 can only be accessed when the host has IPv4 connectivity. In
IPv4/IPv6 transition scenario, the Host may be in an IPv6 only network
as described in the PNAT draft.

In that case, we cannot use DHCPv4 to assign IP address for the host.
Instead, we propose to assign an IPv4 address and an IPv6 prefix to
the host using DHCPv6,  the host then uses the IPv4 address together
with the IPv6 prefix to synthesize an IPv6 address as its source
address.

---

From: Tim Chown <[email-masked]>
Date: Tue, 21 Jul 2009 14:51:00 +0100

> ==> I agree, this is what we think and then proposed in behave working group.

RFC4477 stated reasonably clearly that it was 'current consensus' that was
made in the absence of widespread operational experience.  

The context of RFC 4477 was considering DHCP behaviour/best practice in
a dual-stack network, i.e. IPv4 and IPv6 transport available to the host.
There is some discussion in section 4.2 on obtaining IPv4 addresses
via DHPCv6, and a list of concerns at the time about this approach.  These
may not be so important if there is a specific use case where the potantial
issues are avoided, e.g. no danger of a host getting IPv4 addresses via a 
DHCPv6 option *and* via regular DHCPv4.

The idea of carrying IPv4 address options via DHCPv6 is not new - it was
suggested many years ago as a method for a DSTM host to get an IPv4 address 
to use for its IPv4-in-IPv6 tunnel to an edge router.   I'm sure the draft(s)
associated with that idea are online somewhere - there were implementation(s).

Tim

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From: Ted Lemon <[email-masked]>
Date: Wed, 22 Jul 2009 13:15:18 +0100

Okay, this makes sense now--thanks for clarifying!

Sent from my iPhone