Re: [mif] Review requested: draft-ietf-mif-dhcpv6-route-option

[Alexandru Petrescu <[e-mail]>]

Le 31/10/2011 18:38, Tomasz Mrugalski a écrit :
> On 31.10.2011 18:16, Alexandru Petrescu wrote:
>> Le 30/10/2011 18:24, Ted Lemon a écrit :
>>> On Oct 30, 2011, at 1:02 PM, Alexandru Petrescu wrote:
>>>> The question one raised on 6man is about coexistence with RA
>>>> about default route. One is aware that a similar situation
>>>> (alternate mechanism DHCP-vs-RA for default route) appeared
>>>> recently when DNS-in-RA was proposed (DHCP existed doing DNS).
>>>> RFC6106 proposes to do DNS-in-RA but has a section explaining
>>>> coexistence with DHCP about DNS address - and gives the latter
>>>> precedence over.
>>>
>>> This is a very good point, which should be addressed in the
>>> route option draft. I think the right thing is to give RA
>>> precedence over DHCP for routing information, but am curious to
>>> know if others disagree.
>>
>> I do not disagree: in the default route case, if RA offers such
>> data then give it preference over the default route obtained from
>> DHCP.
>
> Sorry, but I can't parse that sentence. You seem to agree with Ted
> (DHCP preferred over RA), but the later part of the sentence states
> otherwise (RA preferred over RA).

Ted suggested RA to be prefered over DHCP and I agree with it.

(in another email you propose DHCP preferred over RA, and Ted seems to
agree with you as well).

>> (the preference mechanism can be specified by using the lifetime
>> mechanism).
>
> Can you elaborate on that? What has lifetime to do with preference?
> Do you want to somehow prefer longer (or shorter) lifetimes?

YEs, that.  RA has this Router Lifetime field.  When two routers send RA
each with a default default router, the Host could 'prefer' one over the
other based on the longest lifetime.  RFC4861 says 'The Router Lifetime
applies only to the router's usefulness as a default router'.

A similar mechanism could happen to compare a default route obtained
from DHCP, and from RA: prefer the one whith longer lifetime.

> That is rather dangerous and I would like to avoid that. I believe
> that clear statement ("DHCP overrides RA" or "RA overrides DHCP")
> will help a lot here.

Hm, but that's not how DNS-RA RFC does.  DNS-RA RFC6106 does preferences
instead of a yes-no alternative.  RFC4191 "Default Router Preferences"
also works with preferences instead of exclusion.

What do you think?

Alex

>
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