Subject: Re: [dhcwg] DHCPv6 Server Option in RA

From: Huan Huan <[email-masked]>
Date: Thu, 4 Feb 2010 10:16:32 +0800

Hi,

In my understanding, the relay agent can't forward the RA message, unless it
also have a routing function. But a relay agent will
encapsulate/decapsulation for "Information-Request" message and other dhcp
reply messages with the request information.

>
> Message: 3
> Date: Wed, 3 Feb 2010 08:29:10 -0600
> From: "Wes Beebee (wbeebee)" <[email-masked]>
> Subject: Re: [dhcwg] DHCPv6 Server Option in RA
> To: "Xu Xiaohu" <[email-masked]>, <[email-masked]>
> Message-ID:
>        <[email-masked]>
> Content-Type: text/plain;       charset="gb2312"
>
> What happens if there is a relay agent on the link and the DHCPv6 Stateless
> Server Option is provided in the RA as well as O=1?
>
> Does the DHCPv6 Stateless Server Option take precedence over the relay
> agent?
>
> Wes Beebee
> Software Engineer
> Product Development
> [email-masked]
>
> United States
> Cisco.com - http://www.cisco.com
> For corporate legal information go to:
> http://www.cisco.com/web/about/doing_business/legal/cri/index.html
>
>
> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On Behalf Of
> Xu Xiaohu
> Sent: Tuesday, February 02, 2010 10:29 PM
> To: [email-masked]
> Subject: Re: [dhcwg] DHCPv6 Server Option in RA
>
> Hi all,
>
> Is there any objection to this Stateless DHCPv6 Server Option in RA?
>
> Xiaohu
>
> > -----????-----
> > ???: Xu Xiaohu [mailto:[email-masked]]
> > ????: 2010?1?29? 9:47
> > ???: [email-masked]'
> > ??: FWD: DHCPv6 Server Option in RA
> >
> >
> >
> > Hi all,
> >
> > Since the following discussion is related to DHCPv6, especially
> > stateless DHCPv6, I forward it here.
> >
> > Any comment is appreciated!
> >
> > Best wishes,
> > Xiaohu
> >
> > > -----????-----
> > > ???: Xu Xiaohu [mailto:[email-masked]]
> > > ????: 2010?1?28? 12:15
> > > ???: 'IETF IPv6 Mailing List'
> > > ??: DHCPv6 Server Option in RA
> > >
> > > Hi all,
> > >
> > > In a scenario where hosts have obtained IPv6 addresses through some
> other
> > > mechanism, such as stateless address auto-configuration or manual
> > > configuration while other configuration parameters (e.g., recursive
> > > DNS servers)are learnt via stateless DHCPv6 [RFC 3736], would it be
> > > better
> for
> > these
> > > hosts to obtain the DHCPv6 server addresses via a new RA option in
> advance?
> > > Thus these hosts could directly send unicast DHCP
> > > Information-request
> > messages
> > > to the stateless DHCP server without the need of DHCP relay agent
> between
> > the
> > > client and server. As a result, delays due to the relaying of
> > > messages
> by
> > relay
> > > agents, as well as overhead and duplicate responses by servers due
> > > to
> the
> > > delivery of client messages to multiple servers can be avoided.
> > >
> > > Meanwhile, I noticed there is a statement about unicast DHCP request
> > > in
> the
> > > DHCPv6 specification [RFC 3315] as follows:
> > >    "When the server receives a Request message via unicast from a
> client
> > >    to which the server has not sent a unicast option, the server
> > >    discards the Request message and responds with a Reply message
> > >    containing a Status Code option with the value UseMulticast, a
> Server
> > >    Identifier option containing the server's DUID, the Client
> Identifier
> > >    option from the client message, and no other options."
> > >
> > > Unless the unicast option is not available for all clients, I
> > > believe it
> would
> > > conflict with the basic principle of stateless DHCP that DHCP server
> needs
> > not
> > > to maintain per host state.
> > >
> > > There is another statement about the unicast DHCP request in RFC
> > > 3315 as
> > > follows:
> > >       " ...Use of unicast may avoid delays due to the relaying of
> messages
> > by
> > >       relay agents, as well as avoid overhead and duplicate responses
> by
> > >       servers due to the delivery of client messages to multiple
> > >       servers.  Requiring the client to relay all DHCP messages through
> > >       a relay agent enables the inclusion of relay agent options in all
> > >       messages sent by the client.  The server should enable the use of
> > >       unicast only when relay agent options will not be used. "
> > >
> > > Judging from the above statement, especially the last sentence, it
> > > seems
> that
> > > the relay agent is preferred. Then what's the reason for that
> preference?
> > To
> > > prevent flood attack on the DHCP server? If the answer is yes, then
> > > as
> for
> > > stateless DHCP, it seems that such attacks are not much serious
> > > since
> the
> > > stateless DHCP server doesn't need to maintain any dynamic state for
> > individual
> > > clients. At least, not worse than flood attacks on DNS servers.
> > >
> > > Comments?
> > >
> > > Xiaohu
>
>
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>
>
-- 
Huan Huan

BII Group
IPv6 R&D Center
Technique Project Manager