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Re: IPv6 RA vs DHCPv6 - The chosen one?
From: Tomas Podermanski <tpoder () cis vutbr cz>
Date: Thu, 22 Dec 2011 21:09:28 +0100

Hi,

On 12/22/11 12:04 AM, Michael Sinatra wrote:
On 12/21/11 12:40, Ray Soucy wrote:
I'm afraid you're about 10 years too late for this opinion to make
much difference. ;-)

We have been running IPv6 in production for several years (2008) as
well (answering this email over IPv6 now, actually) yet I have
completely different conclusions about the role of RA and DHCPv6.
Weird.

And that's a very good reason not to deprecate SLAAC.  Tomas may
prefer DHCPv6, and he may provide reasons others may prefer DHCPv6. 
But he hasn't provided justification for deprecating SLAAC.
I am not against SLAAC. I am against the way how DHCPv6 & SLAAC works
today. Today, SLAAC can not live without DHCPv6 and DHCPv6 can not live
without SLAAC (RA). Second reason is that we have two
protocols/techniques to do just the same thing. I prefer to have just
ONE common autoconfiguration method as we have it in IPv4. Because
DHCPv6 is more complex and SLAAC can provide only subset of DHCP
functionality I personaly prefer DHCPv6.


Many of us have been working with IPv6 for years and have found SLAAC
to be quite useful.  The biggest benefit it provides, which Tomas did
not acknowledge, is the ability to autoconfigure hosts without running
a central server.  That said, I have also found DHCPv6 to be quite
useful.

We have to use SLAAC as well because we do not have other choice. Not
all operating systems supports DHCPv6 today. But we are not happy about
it (problems with privacy extensions, security as I mentioned before).

DHCPv6 do not have to be run on a central server. DHCPv6 can be
implemented as a part of a router as well. It is common for DHCP(v4) an
implementations for DHCPv6 are available today (eg. cisco
http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-dhcp.html).


I also agree with Owen: Provide two complete solutions, and let
operators choose based on their needs.  That implies fixing DHCPv6 so
I don't have to go in and disable the autonomous flag on my routers
and run RAs just to get a default route.  But it also implies not
deprecating either SLAAC or DHCPv6.

Although we have differed opinion whether we need one or two
autoconfiguration protocols, I totally agree that "fixing" DHCPv6 is a
really necessary step and It should have been done many years ago.

Btw. not all people agree that DHCPv6 should be fixed in that way. There
was a discussion in 2009 in dhcwg (thread available on:
http://www.ietf.org/mail-archive/web/dhcwg/current/msg09715.html). The
current draft (draft-ietf-mif-dhcpv6-route-option-03)  is the 3rd
attempt to do it. In past, there were another two drafts trying to
introduce route information into DHCPv6:

draft-droms-dhc-dhcpv6-default-router-00, expired September 2009
draft-dec-dhcpv6-route-option-05, expired  April 2011

So I hope that this time we will have more luck :-)


Tomas



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