Subject: Re: [dhcwg] draft-lourdelet-radext-ipv6-dhcp-00 published

From: Mohacsi Janos <[email-masked]>
Date: Wed, 30 Jul 2008 12:23:17 +0200 (CEST)

Dear All,

Firstly sorry for cross posting....

As I mentioned in the dhc wg meeting in my opinion the document has to be 
improved on topic dynamically assign IPv6 addresses:

>From operational point of view If you want to add an IP address to and you 
have to specify the prefix length also. There are two options:

1. Either stick to the what is defined RFC 4291, RFC 4861, RFC 4862 - 
learn prefix length via Stateless Address configuration

- I think this is acceptable, but I think implementation point of view it 
has some difficulties (in the time of assignment of IPv6 address on IPv6 
host, node has to lookup current on-link prefix length from RA cache...)

In this case the document should sprecify this consideration....

2. Supply prefix length with IP address - in radius, also in DHCPv6 - and 
assign to interface.

Advantage of this solution you have freedom to choose whatever prefix 
length you like for your subnets - not only /64. Also address and prefix 
length is handled together... Which i more natural.

Drawback of this setup is that you have to add support this new prefix 
length option in all DHCPv6 implementation.

Best Regards,

Janos Mohacsi
Network Engineer, Research Associate, Head of Network Planning and Projects
NIIF/HUNGARNET, HUNGARY
Key 70EF9882: DEC2 C685 1ED4 C95A 145F  4300 6F64 7B00 70EF 9882

On Thu, 12 Jun 2008, Benoit Lourdelet (blourdel) wrote:

>
> Hello,
>
> I published a document specifying new RADIUS  attributes supporting IPv6
> network access to complement [RFC3162] in DHCP environments. It
> addresses the need to dynamically advertise DNS Server addresses and one
> or multiple IPv6 addresses via DHCPv6.
>
> It is available here :
> http://www.ietf.org/internet-drafts/draft-lourdelet-radext-ipv6-dhcp-00.
> txt
>
> Comments are welcome.
>
> Regards
>
> Benoit Lourdelet
>
>
>
> A new version of I-D, draft-lourdelet-radext-ipv6-dhcp-00.txt has been
> successfully submitted by Benoit Lourdelet and posted to the IETF
> repository.
>
> Filename: draft-lourdelet-radext-ipv6-dhcp
>
> Revision: 00
>
> Title: IPv6 RADIUS attributes for DHCP based networks
>
> Creation_date: 2008-06-12
>
> WG ID: Independent Submission
>
> Number_of_pages: 8
>
> Abstract:
>
> This document specifies RADIUS [RFC2865] attributes supporting IPv6
> network access to complement [RFC3162] in DHCP environments. It
> addresses the need to dynamically advertise DNS Server addresses and one
> or multiple IPv6 addresses via DHCPv6.
>
> _______________________________________________
> dhcwg mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/dhcwg
>
_______________________________________________
dhcwg mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/dhcwg

---

From: Ralph Droms <[email-masked]>
Date: Wed, 30 Jul 2008 06:31:42 -0400

In the IPv6 specs, informing a host of the prefixes on a link is  
accomplished solely through RAs.  Address assignment is accomplished  
through DHCPv6.  There is no implication in DHCPv6 that the prefix  
from an address is assigned to the link to which the related interface  
is attached.  Therefore, there is no reason to include a prefix length  
with an assigned address in DHCPv6 - that prefix will be announced  
through RAs.

- Ralph

On Jul 30, 2008, at 6:23 AM, Mohacsi Janos wrote:
> As I mentioned in the dhc wg meeting in my opinion the document has  
> to be improved on topic dynamically assign IPv6 addresses:
>
> From operational point of view If you want to add an IP address to  
> and you have to specify the prefix length also. There are two options:
>
> 1. Either stick to the what is defined RFC 4291, RFC 4861, RFC 4862  
> - learn prefix length via Stateless Address configuration
>
> - I think this is acceptable, but I think implementation point of  
> view it has some difficulties (in the time of assignment of IPv6  
> address on IPv6 host, node has to lookup current on-link prefix  
> length from RA cache...)
>
> 2. Supply prefix length with IP address - in radius, also in DHCPv6  
> - and assign to interface.
>
> Advantage of this solution you have freedom to choose whatever  
> prefix length you like for your subnets - not only /64. Also address  
> and prefix length is handled together... Which i more natural.
>
> Drawback of this setup is that you have to add support this new  
> prefix length option in all DHCPv6 implementation.
>
> Best Regards,
>
> Janos Mohacsi

---

From: Mohacsi Janos <[email-masked]>
Date: Wed, 30 Jul 2008 13:45:47 +0200 (CEST)

On Wed, 30 Jul 2008, Ralph Droms wrote:

> In the IPv6 specs, informing a host of the prefixes on a link is accomplished 
> solely through RAs.  Address assignment is accomplished through DHCPv6.

"As a devil's advocate"
I think the prefix announced via router advertisement is only related to 
the stateless address autoconfiguration.
So the address assigned via DHCPv6 is assigned to interface with /128?

Is it what we want?

> There is no implication in DHCPv6 that the prefix from an address is assigned 
> to the link to which the related interface is attached.  Therefore, there is 
> no reason to include a prefix length with an assigned address in DHCPv6 - 
> that prefix will be announced through RAs.

What about the scenario where there is no router in the network or not 
announcing router advertisement with prefix options? What length of prefix 
the DHCPv6 client should use for address assignment?

Best Regards,
 	Janos

>> 1. Either stick to the what is defined RFC 4291, RFC 4861, RFC 4862 - learn 
>> prefix length via Stateless Address configuration
>>

---

From: "Hemant Singh (shemant)" <[email-masked]>
Date: Wed, 30 Jul 2008 08:01:15 -0400

>What about the scenario where there is no router in the network or not
announcing router advertisement with prefix options? What length of
prefix the >DHCPv6 client should use for address assignment?

> 	Janos

There is no provision in DHCPv6 to include prefix length in a message to
the client - I have said so several times to the DHCPv6 mailer.  Check
the email archives.  In a router-less network, you are hosed.  You have
to configure an address and prefix length manually.

Hemant

---

From: Mohacsi Janos <[email-masked]>
Date: Wed, 30 Jul 2008 14:16:19 +0200 (CEST)

> to configure an address and prefix length manually.

If I were and enterprise system administrator I would stick to DHCP. 
Therefore for introducing IPv6 I would like to use DHCPv6 - minimal router 
support since I have no control over router - different department 
operating the network.
I would ask network operating department to inform hosts with M bit that 
they should use DHCPv6 and not announcing prefix and prefix length since 
as an enterprise system admin I would like to control the host 
configuration... This is what I get used to in DHCPv4 environment...

I am not a system admin, therefore I can admit, that I cannot control 
address configuration of the hosts...

But It has to be documented:

Don't do DHCPv6 without announcing the prefix and prefix length via Router 
Advertisements.

Regards,
 	Janos Mohacsi

---

From: "Bernie Volz (volz)" <[email-masked]>
Date: Wed, 30 Jul 2008 08:44:27 -0400

If you have no router, why do you need anything but link-local
addresses.

--

At the present time, RAs (and manual configuration) are the ways in
which prefix information is distributed (to be fully correct, there is
also DHCPv6 PD and I may also be leaving out some other mechanisms?).
There have been discussions in the past about changing this by allowing
DHCPv6 (when used for address assignment) to provide that information,
but that work has not progressed (see
http://www.ietf.org/proceedings/07jul/slides/dhc-5.pdf).

- Bernie

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of Mohacsi Janos
Sent: Wednesday, July 30, 2008 8:16 AM
To: Hemant Singh (shemant)
Cc: [email-masked]; [email-masked]; Ralph Droms (rdroms)
Subject: Re: [dhcwg] draft-lourdelet-radext-ipv6-dhcp-00 published

If I were and enterprise system administrator I would stick to DHCP. 
Therefore for introducing IPv6 I would like to use DHCPv6 - minimal
router 
support since I have no control over router - different department 
operating the network.
I would ask network operating department to inform hosts with M bit that

Don't do DHCPv6 without announcing the prefix and prefix length via
Router 
Advertisements.

Regards,
 	Janos Mohacsi

---

From: "Bernie Volz (volz)" <[email-masked]>
Date: Wed, 30 Jul 2008 08:53:39 -0400

Actually, that work is still very active - see
http://www3.ietf.org/proceedings/08jul/slides/v6ops-7.ppt (to be
presented on Thursday, July 31),
http://www.ietf.org/proceedings/07dec/slides/v6ops-1/sld1.htm and
http://www.ietf.org/internet-drafts/draft-chown-v6ops-rogue-ra-01.txt.

Sorry Tim and Stig!

- Bernie 

-----Original Message-----
From: Bernie Volz (volz) 
Sent: Wednesday, July 30, 2008 8:44 AM
To: 'Mohacsi Janos'
Cc: [email-masked]; [email-masked]; Ralph Droms (rdroms)
Subject: RE: [dhcwg] draft-lourdelet-radext-ipv6-dhcp-00 published

--

- Bernie

-----Original Message-----

Regards,
 	Janos Mohacsi

---

From: Mohacsi Janos <[email-masked]>
Date: Wed, 30 Jul 2008 15:18:23 +0200 (CEST)

Hi,

There is a progress on the draft you cited:

http://www.ietf.org/proceedings/08jul/agenda/v6ops.html

Tim will present rogue RA issues, me about our RA-guard proposal.
However I don't think that prefix length assignment problem  has been 
noted by rogue RA draft...

Anyway in routerless environment you don't need anything else than 
link-local.

However As mentioned there is router equipped environment, where hosts 
might have no clue about the prefix length...

Regards,

Janos Mohacsi

---

From: Tim Chown <[email-masked]>
Date: Wed, 30 Jul 2008 15:06:40 +0100

Well, the prefix information discussion arose out of the Rogue RA discussion,
so was captured in that draft, perhaps not the best place.

I think the suggestion that prefix information via DHCP was desirable came
in part out of the change in RFC4861 of the default 'on link assumption'.
Knowledge of prefix length is also useful.

Tim

-- 
Tim

---

From: Ralph Droms <[email-masked]>
Date: Wed, 30 Jul 2008 10:23:07 -0400

Correction.  On a link with no router advertisements you need to  
configure any addresses and prefixes manually and separately.

There is no expectation that the prefix from an assigned address is  
necessarily on the link.  On-link prefixes are independent from  
assigned addresses.

- Ralph