Re: WPD-6, WAA-8, and WAA-9 of draft-ietf-v6ops-ipv6-cpe-router-04

[Ole Troan <ot@cisco.com>]

Philip,

>> part       text/plain                1708
>>> WPD-6:
>>>   Absent of other routing information the IPv6 CE router MUST
>>>   use Router Discovery as specified in [RFC4861] to discover a
>>>   default router(s) and install default route(s) in its routing
>>>   table with the discovered router's address as the next-hop.
>>> 
>>> RFC-4861 describes how routers process Router Advertisements (mainly to
>>> check them for consistency). Only hosts maintain a list of default routers.
>> 
>> that's why the upstream interface is specified as behaving as a
>> host for some functions. see W-1.
> 
> For acquiring a global address. It doesn't say anything about after that. Does
> it remain a host until a default route is installed? How does it handle 
> expiring the router router. Or is the first router that replies installed there
> forever?

for the purpose of acquiring an address it will behave like a host. equally with expiring a router learnt via router discovery. of course it is acting as a router for all other purposes.

I'm not that keen on using router discovery either, but as a last resort do you have any better idea?

>>> It looks like that at least one ISP treats this draft BCP as gospel. So I
>>> wonder whether the draft should mandate the weak host model. I can't think
>>> of anything negative that would happen if a CPE assigns in WAA-8 the addres
>> s
>>> not to a virtual interface but to its WAN interface and then implements the
>>> strong model.
>> 
>> that would violate rfc3633. which require that a delegated prefix
>> isn't used on the link between the RR and the DR. routers are
>> generally following the weak host model, any particular reason why
>> you require the strong host model?
> 
> I never expected a DHCP RFC to effectively mandate the weak multi host model.
> Weird.

it doesn't. the need for the 'unnumbered' WAN interface does.
I don't know of any router implementation which doesn't implement the weak host model, but I'm not aware of that being specified anywhere either.

> Because the CPE is essentially always-on it is very tempting to add other host
> functionality, like a file server, a web server for the customers's pictures
> and videos, maybe a SIP gateway, etc. As such it may acquire other prefixes
> as well, maybe ULA, maybe as part of multi homing, prefixes from other
> providers.
> 
> With the strong host model, you know from with interface addresses are going to
> be selected for sending error ICMPs. With the weak multi homing model it is
> anyones guess.
> 
> How do prevent to router from using the wrong address for sending an error
> ICMP?

it will pick the best source for the purpose, see RFC4443. just like any other multi-homed implementation. see also rfc3484.

cheers,
Ole