Subject: Re: [dhcwg] DHCPv6 Stateful Prefix Length

From: Alain Durand <[email-masked]>
Date: Mon, 01 Oct 2007 08:32:34 -0400

On 9/28/07 8:21 PM, "Ralph Droms" <[email-masked]> wrote:

> 
> 
> There has been a proposal to provide prefix information to hosts
> through DHCPv6 in addition to RAs.  The correct way to provide that
> information would be to include a list of prefixes and associated
> prefix lengths in the DHCPv6 message sent to the client.  Simply
> associating a prefix length with the assigned addresses would not
> provide the appropriate information to the host.
> 

====> Actually, I would disagree with you... As I explained in an earlier
mail,
            RA & DHCP messages have different scopes, one is link local, the
other one
            can carry information limited to a single prefix on that link.
            If you want to build multiple logical L3 subnets on the same
link, the difference
            is important. So, I¹d rather see a prefix len option associated
to the address
            rather than re-defining the exact semantic of RA within DHCPvy6
messages
            just for the sake of replacing RA.

      - Alain.

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From: "David W. Hankins" <[email-masked]>
Date: Mon, 1 Oct 2007 09:15:00 -0700

>             is important. So, I¹d rather see a prefix len option associated

DHCP can carry information limited to a single host computer, of which
the specific prefix(es) to which it is attached are a subset.

If you wanted to deliver different PIO contents to different classes
of clients (for any reason), RA makes this very hard - if not
impossible, such as if you do not control the "downstream" ethernet
switch's idea of 'broadcast' or anywhere multiple clients share one
physical media (wireless).

These kinds of 'classifications' of clients are also generally done
beyond the network's heart - its administrative center - and not at
the multiple edge devices scattered around the network.

So, there's one critical piece of information missing here.  There
was going to be an updated draft, seeking to be a WG item, with the
many "problem descriptions" and (a?) proposed solution.

Can we identify that draft's author, and get an update on their
progress?

These sorts of discussions are useful if we're filling a new author's
head with ideas to argue in a new draft they will theoretically write,
but arguing about the merits or deficits of a draft that we have not
yet seen is a bit premature...

-- 
Ash bugud-gul durbatuluk agh burzum-ishi krimpatul.
-- 
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
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From: Ralph Droms <[email-masked]>
Date: Thu, 4 Oct 2007 17:26:44 -0400

I don't understand what you mean by "one is link local, the other one  
can carry information limited to a single prefix on that link".  I  
understand the difference between RA and DHCP to be that the RA  
applies to all hosts on a link while DHCP can provide different  
information to each host.  One application might be to inform host A  
that it should regard prefix 2001:0:0:1::/64 as on-link, and to  
inform host B that it should regard prefix 2001:0:0:2::/64 as on-link.

On the other hand, it is perfectly reasonable that the network admin  
might want to inform host A that it should assign address  
2001:0:0:1::1 to its interface, and consider both 2001:0:0:1::/64 and  
2001:0:0:2::/64 as on-link.

TMy point is that DHCP could be used to inform the host about  
prefixes other than those from which the host has assigned  
addresses.  Therefore, we would need a separate option carrying  
prefix information.  While including a prefix length with an assigned  
address might be a useful shorthand, for simplicity I believe a  -mx.ietf.org with esmtp (Exim 4.43) id 1IdcAc-0001XJ-41
	for [email-masked]; Thu, 04 Oct 2007 21:40:08 -0400
From: Ralph Droms <[email-masked]>
Subject: Re: [dhcwg] DHCPv6 Stateful Prefix Length
Date: Thu, 4 Oct 2007 17:26:44 -0400
To: Alain Durand <[email-masked]>
Cc: [email-masked], Ralph Droms <[email-masked]>

I don't understand what you mean by "one is link local, the other one  
can carry information limited to a single prefix on that link".  I  
understand the difference between RA and DHCP to be that the RA  
applies to all hosts on a link while DHCP can provide different  
information to each host.  One application might be to inform host A  
that it should regard prefix 2001:0:0:1::/64 as on-link, and to  
inform host B that it should regard prefix 2001:0:0:2::/64 as on-link.

On the other hand, it is perfectly reasonable that the network admin  
might want to inform host A that it should assign address  
2001:0:0:1::1 to its interface, and consider both 2001:0:0:1::/64 and  
2001:0:0:2::/64 as on-link.

TMy point is that DHCP could be used to inform the host about  
prefixes other than those from which the host has assigned  
addresses.  Therefore, we would need a separate option carrying  
prefix information.  While including a prefix length with an assigned  
address might be a useful shorthand, for simplicity I believe a  
separate option would be a better design choice.

- Ralph

On Oct 1, 2007, at Oct 1, 2007,8:32 AM, Alain Durand wrote:

> ====> Actually, I would disagree with you... As I explained in an  
> earlier mail,
>             RA & DHCP messages have different scopes, one is link  
> local, the other one
>             If you want to build multiple logical L3 subnets on the  
> same link, the difference
>             is important. So, I’d rather see a prefix len option  
> associated to the address
>             rather than re-defining the exact semantic of RA within  
> DHCPvy6 messages

separate option would be a better design choice.

- Ralph

On Oct 1, 2007, at Oct 1, 2007,8:32 AM, Alain Durand wrote:

> ====> Actually, I would disagree with you... As I explained in an  
> earlier mail,
>             RA & DHCP messages have different scopes, one is link  
> local, the other one
>             If you want to build multiple logical L3 subnets on the  
> same link, the difference
>             is important. So, I’d rather see a prefix len option  
> associated to the address
>             rather than re-defining the exact semantic of RA within  
> DHCPvy6 messages