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RE: Posted a new copy of CPE Rtr draft
Hello,
I agree with you on two aspects:
- in a broadband access environment the CPE router requires not only the IPv6 address but also additional configuration info like DNS, NTP and so on, and I agree DHCP is a good tool to be used for this purpose.
- as SP, we need to have centralized administrative control of the CPE router both to centralize the prefix distribution and to simplify, as you pointed out, troubleshooting and billing procedures. My point is that the DHCP Server is not the only possible centralized point of our network. Today for IPv4 we can use AAA Radius server to store subscribers profile, thus moving to IPv6 one option could be to keep a similar approach and store IPv6 prefix in AAA radius server then use RADIUS attributes to influence DHCP tasks.
The difference I see between using SLAAC vs steful DHCPv6 to number WAN link comes in the picture if you consider both a scenario where there is a routed CPE and a scenario where there are hosts directly connected to the SP network (you can see this second case either like a migration step where some customers still have an old IPv4 only CPE that simply behaves as bridge for IPv6 connections or a Wimax access where there is no CPE.) . When I use WAN numbered model I need to provide to my customer at least one IPv6 address for the WAN link and delegate a prefix to number the home network, from the AAA RADIUS perspective it would be desirable to use a common address allocation method in both scenarios described above. If I use SLAAC + DHCP-PD I do not need to know at the session set up time if my customer has a routed CPE thus that /64 is used to number the WAN link or if there is an host behind a legacy IPv4 only CPE thus that /64 is used to number the host interface. In both cases my AAA Radius Server will have a /64 for SLAAC and a /x (probably /56) for DHCP PD. In both scenarios DHCP stateless is still used to obtain other configuration parameters.
In my opinion even with SLAAC using AAA RADIUS you can achieve centralized administrative control. Any comments?
> Would you rather the specification *recommend* SLAAC? If so, do you have a recommendation regarding > the other matters? Would you prefer that the document simply recommend that CPE equipment support
> both options?
I'm not saying one approach is better than other I was trying to understand the reasons behind the recommendation made in the draft. You may consider the scenario I described before out of scope, but I would prefer the document recommend that CPE equipment support both SLAAC and stateful DHCPv6.
Anyway I interesting in hearing both your comments and additional opinions.
Thanks,
Best Regards,
Roberta
-----Original Message-----
From: Mark Smith [mailto:ipng@69706e6720323030352d30312d31340a.nosense.org]
Sent: Monday, March 16, 2009 9:39 PM
To: Fred Baker
Cc: Maglione Roberta; 'Hemant Singh (shemant)'; Wes Beebee (wbeebee); IPv6 Operations
Subject: Re: Posted a new copy of CPE Rtr draft
On Mon, 16 Mar 2009 11:22:42 -0700
Fred Baker <fred@cisco.com> wrote:
>
> On Mar 16, 2009, at 5:55 AM, Maglione Roberta wrote:
>
> > could you please explain why stateful DHCPv6 is the recommended
> > method for assigning a global IPv6 address to the WAN interface?
> > Are you suggesting excluding the possibility to use SLAAC to number
> > WAN interface?
>
> I don't understand him to be *precluding* anything. However, I do
> believe that he is saying that an ISP generally has more to configure
> on a CPE router than the interface address; it will have the
> recommended DNS server, the prefix that the SOHO/Residence will subnet
> internally, if DS-Lite is in use it will have the necessary
> information to configure a tunnel, and so on. He is saying that if
> that is the case, one may as well get the interface address from the
> DHCP server as well.
>
> I think the question before the house is whether the ISPs, such as
> Telecom Italia, agree with that viewpoint. Certainly you can *use*
> SLAAC in your network. Would you rather the specification *recommend*
> SLAAC? If so, do you have a recommendation regarding the other
> matters? Would you prefer that the document simply recommend that CPE
> equipment support both options?
>
> I am not expressing an opinion here; I know of networks in which DHCP
> seems like a better choice and networks in which SLAAC is a perfectly
> reasonable solution. I think it is important that you - and other ISPs
> - state their opinions however.
>
(not representing a ISP here, but work at one, and these
sorts of issues are some of the ones I have to worry about)
I think DHCP is the better option. The link to the customer's WAN
interface is the first customer unique or specific part of the
network connection, so having some non-upstream-router harder or hard
state in your management systems i.e. DHCP database, can make
troubleshooting and billing easier. It also encourages the model that
ISPs give out subnets to all customers (unless there is a PD option for
RAs that I'm not aware of), not end-node addresses.
Regards,
Mark.
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