Re: RS sending in draft-ietf-v6ops-ipv6-cpe-router-04

[Philip Homburg <pch-v6ops@u-1.phicoh.com>]

In your letter dated Wed, 28 Apr 2010 21:47:25 +0200 you wrote:
> > Some ISP do not assign any address to the WAN link and the DHCP-DP RFC prev
> ents
> > me from assigning a address from the prefix to that link. That annoys me to
>  no
> > end.
> 
> I don't understand what the problem with this is. the CPE draft
> recommends that an address is configured on an internal interface.
> why does it matter to which interface the address is on?

Because, with picking a global address from a random interface it is mich
harder to ensure the ICMP error gets te source address I want it to have.

And also because the reason for disallowing it is not all that strong.

> > But worse, when every ISP comes up with an arbitrary list of features (and
> > requirements) it becomes almost impossible to help a random person with his
> > internet connection.  Oh, you don't have a global IP address on WAN link, i
> s
> > that normal because the ISP doesn't assign one, or did something go wrong?
> > Neighbor discovery doesn't work, is that normal because the ISP disabled it
> ,
> > or is something really broken. You only know if you know the details of
> > every ISP.
> 
> what arbitrary features are those? there are 3 addressing models.
> SLAAC, DHCPv6 and "unnumbered".  all models use SLAAC.  ND is used.
> I'm not aware of anything that requires 'details of every ISP' to
> understand.

If you come across a CPE that fails in some unspecified way (somebody asked you
for help because the Internet is down or something like that) how do know
what is normal or not?

Not all CPE have extensive debug interfaces where you dump all packets.

If all links have global IP addresses then you know what is going on if you
find one that doesn't.

I don't know about the 'ND is used' part. But my ISP's router does not respond
to NS messages (on a PPP link). I think they believe that that's allowed by
the standards. Are you saying it isn't?

> > But more practically speaking, how do you know the global IPv6 address of
> > your customer? With SLAAC you would have to know the MAC address to even
> > guess that address. Do you guess it based on the link-local address? Do you
> > call the customer? What if the customers CPE uses temporary (privacy)
> > addresses?
> 
> if you are an SP that requires to know the customers address, then
> you use DHCPv6 for address assignment.


> > With prefix delegation, a router is very likely to have at least one global
> > address from the delegated prefix.
> 
> yes. are you arguing that this address should be well known? since
> there is no way you can assign that via DHCP. or are you arguing
> that there should be a mechanism to discover it? e.g by using the
> subnet-router anycast address?

If people want to ping routers that get a prefix using PD then that seems to
be a sensible approach.