Re: [dhcwg] RFC 3633 to Internet Standard

Ralph Droms <rdroms.ietf@gmail.com> Wed, 02 October 2013 12:16 UTC

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From: Ralph Droms <rdroms.ietf@gmail.com>
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To: Leaf Yeh <leaf.yeh.sdo@gmail.com>
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Cc: "dhcwg@ietf.org WG" <dhcwg@ietf.org>, Alexandru Petrescu <alexandru.petrescu@gmail.com>
Subject: Re: [dhcwg] RFC 3633 to Internet Standard
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On Oct 1, 2013, at 11:39 AM 10/1/13, Leaf Yeh <leaf.yeh.sdo@gmail.com> wrote:

> Ralph - How does the Access Router know the route through the RR to the PC?
> I thought that was the information that needs to be installed on the Access
> Router.
> 
> I guess Ole's answer in the thread of 'Re: [dhcwg] Advancing RFC 3315 and
> RFC 3633 to Internet Standard' was '...everyone does this with snooping
> today...'

But that's snooping on the device on which the relay agent runs.  In the diagram we're discussing, the Access Router doesn't have a relay agent and wouldn't snoop.

- Ralph

> 
> 
> Best Regards,
> Leaf
> 
> 
> 
> -----Original Message-----
> From: dhcwg-bounces@ietf.org [mailto:dhcwg-bounces@ietf.org] On Behalf Of
> Ralph Droms
> Sent: Thursday, September 26, 2013 3:18 AM
> To: Alexandru Petrescu
> Cc: dhcwg@ietf.org WG
> Subject: Re: [dhcwg] RFC 3633 to Internet Standard
> 
> 
> On Sep 25, 2013, at 12:36 PM 9/25/13, Alexandru Petrescu
> <alexandru.petrescu@gmail.com> wrote:
> 
>> Le 24/09/2013 22:43, Ralph Droms a écrit :
>>> 
>>> On Sep 24, 2013, at 2:35 PM 9/24/13, Alexandru Petrescu
> <alexandru.petrescu@gmail.com> wrote:
>>> 
>>>> Le 24/09/2013 10:32, Ralph Droms a écrit :
>>>>> 
>>>>> On Sep 23, 2013, at 3:58 PM 9/23/13, Alexandru Petrescu 
>>>>> <alexandru.petrescu@gmail.com> wrote:
>>>>> 
>>>>>> Le 23/09/2013 15:55, Tomek Mrugalski a écrit :
>>>>>>> On 23.09.2013 13:50, Alexandru Petrescu wrote:
>>>>>>>> Le 22/09/2013 19:57, Leaf Yeh a écrit :
>>>>>>>>> Ralph > The piece of network equipment that implements the 
>>>>>>>>> relay agent routes, and that network equipment *might* also 
>>>>>>>>> need a route.
>>>>>>>>> 
>>>>>>>>> On the PE router implementing relay for DHCPv6-PD, it always 
>>>>>>>>> needs add the associated route for the CE's network of 
>>>>>>>>> delegated prefix. I can't see *might* here.
>>>>>>>> 
>>>>>>>> I agree with the doubt.  I don't see a might, but rather a must. 
>>>>>>>> Otherwise it doesn't work.
>>>>>>>> 
>>>>>>>> But maybe I dont understand the word 'might' as a native speaker 
>>>>>>>> could hear it.
>>>>>>> Relay agent is functionality that can be provided by a piece of 
>>>>>>> software. You can run it on any box that is connected to more 
>>>>>>> than one network. Although typically such a box serves as a 
>>>>>>> router, it doesn't have to.
>>>>>> 
>>>>>> You mean a Relay agent which runs on a pure Host (single real 
>>>>>> interface, no additional virtual/real interfaces)?
>>>>>> 
>>>>>> Even in that case it (or the Router on the same link which is 
>>>>>> connected to the Internet) will need to install a route towards 
>>>>>> the Requesting Router's interface for the delegated prefix.
>>>>> 
>>>>> And there's the exact point of the discussion - if the relay agent 
>>>>> is not implemented on the router that needs the route, passing the 
>>>>> route in the DHCPv6 message exchange through the relay agent won't 
>>>>> get the route to the appropriate router.
>>>>> 
>>>>>> 
>>>>>> In all cases, the Relay and other routers on that link MUST 
>>>>>> install a route.
>>>>> 
>>>>> And how does that route get to the other routers?
>>>> 
>>>> They are all on the same link, and one mechanism used to install 
>>>> routes dynamically is during ICMP Redirect.
>>> 
>>> According to RFC 4861, sec. 8.2, routers ignore ICMPv6 Redirect messages:
>>> 
>>>   A router MUST NOT update its routing tables upon receipt of a
>>>   Redirect.
>>> 
>>> I don't recall if that text is updated by subsequent RFCs.
>> 
>> I don't know either whether subsequent RFCs update it, or whether linux
> has knobs allowing that - one should check.
>> 
>> And, what I meant is not a necessarily a Router but maybe a Host
> DHCPRelay:
>>                       ________ ----------
>>                      |        |DHCPServer|
>>                     ...        ----------
>>                      |
>>   ----------     ---------
>>  | Host     |   | Access  |
>>  | DHCPRelay|   | Router  |
>>   ----------     ---------
>>       |              |
>>   ----+--------------+
>>       |
>>   ----------     ----
>>  |Requesting|   | PC |
>>  | Router   |   |    |
>>   ----------     ----
>>       |            |
>>   ----+------------+--
>> 
>> After the PD phase, and after the assumed route insertion in Access
> Router, the Host DHCPRelay would get an ICMPRedirect from the Access Router
> whenever wanting to talk to PC.  The route it installs is for the Delegated
> Prefix.
> 
> The "Host DHCPRelay" has to be on the same link with the PC.
> 
> How does the Access Router know the route through the RR to the PC?  I
> thought that was the information that needs to be installed on the Access
> Router.
> 
> - Ralph
> 
>> 
>> (the topology above has some advantages in terms of rapid deployment of
> DHCPv6 in a hostpot network).
>> 
>> Alex
>> 
>>> 
>>>> 
>>>>>> Whether they do it at allocation time, at ICMP Redirect time, or 
>>>>>> at manual config time - is another matter.
>>>>> 
>>>>> I'm not saying the route installation can't be accomplished through 
>>>>> DHCPv6.  I think you'll need to address the specific issues I 
>>>>> raised in previous e-mail to publish a specification for passing 
>>>>> routing information to the appropriate router through a DHCPv6 
>>>>> message exchange with a host.
>>>> 
>>>> Ok, my point is whether or not we could formulate a problem 
>>>> statement for this: there is a need for a route in the concerned 
>>>> routers, after the PD operation.  Without that route the 
>>>> communication can't be established between Hosts configured with an 
>>>> address prefixed by the delegated prefix.
>>> 
>>> I agree that there is a need for the route to exist and an appropriate
> problem statement could be formulated.
>>> 
>>> - Ralph
>>> 
>>>> 
>>>> Alex
>>>> 
>>>>> 
>>>>> - Ralph
>>>>> 
>>>>>> 
>>>>>> Without that route the whole schmillblick doesn't work.
>>>>>> 
>>>>>> Alex
>>>>>> 
>>>>>> 
>>>>>> _______________________________________________ dhcwg mailing list 
>>>>>> dhcwg@ietf.org https://www.ietf.org/mailman/listinfo/dhcwg
>>>>> 
>>>>> 
>>>>> 
>>>> 
>>>> 
>>> 
>>> 
>>> 
>> 
>> 
> 
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