Subject: Re: PPP and Global Addresses

From: Nathan Lutchansky <[email-masked]>
Date: Sat, 16 Feb 2002 12:24:35 -0500

IMO, there are two separate scenarios in which some sort of prefix 
delegation needs to be used:

1) A router establishes a point-to-point connection to a provider.
2) A new router is connected to a site's backbone link.

From Brian Haberman's comments at the interim meeting, it seemed that APD 
was designed for scenario (2), providing a means to "grow a network" (his 
words) without need for manual configuration.

However, scenario (1) seems much more common, and indeed was the origin of 
this thread.  Small IPv6 sites are inevitably connected to the 6bone with 
either a p-t-p tunnel or PPP, and there is no good reason we shouldn't 
have some kind of mechanism to autoconfigure the border routers at these 
sites.  A draft by Itojun (draft-itojun-ipv6-dialup-requirement-02.txt) 
describes some of the mechanisms that could be used for configuration, but 
makes no recommendations.

Instead of using a stateful protocol like DHCPv6 or APD to configure
customer sites, perhaps it would be best to use router advertisements on
the p-t-p link.  This was one of the more popular candidates for dialup
configuration during Itojun's presentation in Seattle (the other popular
candidate was APD).  Instead of overloading the Prefix Information option,
however, we could add an additional option to the router advertisement
messages, "Delegated Prefix".  This option could only be used on p-t-p
links, of course.

This technique would be lightweight, would be easy to implement for both
the ISP and client sides, and would provide all the functionality needed
for 90% of sites.  -Nathan

-- 
+-------------------+---------------------+------------------------+
| Nathan Lutchansky | [email-masked] |  Lithium Technologies  |
+------------------------------------------------------------------+
|  I dread success.  To have succeeded is to have finished one's   |
|  business on earth...  I like a state of continual becoming,     |
|  with a goal in front and not behind. - George Bernard Shaw      |
+------------------------------------------------------------------+

---

From: Nathan Lutchansky <[email-masked]>
Date: Tue, 19 Feb 2002 18:12:51 -0500

On Mon, Feb 18, 2002 at 09:07:17AM -0500, Brian Haberman wrote:
>      Since I wasn't at the interim meeting, I am pretty sure that I
> did not make that comment. :)

I'm sorry about that; it must have been Jim Martin since I'm quite sure it 
was one of the authors of the draft.  I apologize for putting words in 
your mouth, but at least I am not misinterpreting your intentions...

> However, the work that has been done
> on automatic prefix delegation is geared mainly towards your point
> (1) below.  In fact, I am in the process of revving the PD draft to
> incorporate comments and suggestions from people who want to use
> PD for CPE-to-ISP connections.

A point was made at the interim meeting (by Tony Hain, I believe, although
I trust my memory less now) that it would be prudent of us to ensure that
the ISP connection procedure for single hosts vs. routers is identical.  
Otherwise, providers will be much more likely to charge extra to connect a
router, which leads to IPv6 NAT, (which leads to anger, which leads to
hate,) which is definitely not what we want to be encouraging.  As I see
it now, using APD for prefix delegation would require routers to start an
APD transaction -- something hosts wouldn't need to do.  Personally, I am
much more likely to endorse a passive mechanism (router advertisements)
than an active mechanism (APD, router renumbering, DHCP), provided there
is no significant disadvantage.

Over the weekend I wrote a draft to define a new option for rtadv messages
to delegate a prefix over a p-t-p link.  I'm trying to keep it as simple
and easy to implement as possible, since any setup that's remotely
complicated should use router renumbering (if that ever gets
standardized).  My draft didn't submitted until today, though, since my
DSL has been down a day or so...  -Nathan

---

From: Francis Dupont <[email-masked]>
Date: Wed, 20 Feb 2002 11:56:32 +0100

In your previous mail you wrote:

   hate,) which is definitely not what we want to be encouraging.

=> I understand the problem but I am afraid this is not possible
with the current way to deal with single hosts, for instance
with a single host the PPP link has a /64 global prefix and with a router
the PPP link has only link-local addresses. The obvious solution is
to use the mechanism for the router case in the single host case too,
but this mechanism is not fully specified and not yet implemented,
at the contrary the current mechanism for single hosts is just plain
RFC 2462.

Regards

[email-masked]

PS: the conclusion is we should specify/finish/implement/deploy router
mechanisms ASAP, at least before IPv6 dialups become common.
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From: "Yamasaki Toshi" <[email-masked]>
Date: Thu, 21 Feb 2002 01:29:44 +0900

> mechanisms ASAP, at least before IPv6 dialups become common.

I absolutely agree. My current conclusion among exsitsing choices is:

- APD for a customer whose CPE is a L3 Router
- RA(+RFC2462, 3041, etc.) for a customer whose CPE is a Multi-link Subnet
Router
- DHCPv6 for a customer who prefer more managed enviroment, that is, DHCP

--- Toshi Yamasaki / NTT Communications