Re: [v6ops] Updating RFC 7084 - alternate logic

[Alexandre Petrescu <[e-mail]>]

Hi, Esko,

Please allow me to express here an oppinion to one particular question
you raise to Tim.

Remark I am not a SNAC expert, for which I am just discovering the IPv6
light bulb concept.

Le 01/12/2022 à 09:11, Esko Dijk a écrit :
> Tim,
> 
> Given all this discussion on the specific prefix allocation policies,
> I wonder if you did intend all of that to be in scope of the RFC 7084
> update?
> 
> For example for SNAC use cases we only need to ensure the CPE / CE 
> router can delegate a /64 if the stub router asks for a /64.  How the
> CE router deals with any other size requests wouldn't be that 
> relevant and could be left to a future update. What are use cases for
> delegation requests for other prefix sizes?

Here is a use case where more than /64 needs to be delegated (absent a
VSLAAC concept): a WiFi AP in router mode deployed in home network, a
WiFi-BT android tablet and a few BT IoT devices.

This is what I have in my home network: a WiFi access point in router
mode, connecting a wifi-BT android tablet and further a few BT IoT
devices (smartwatchesbands and other BT visiting devices for many
reasons like covid-related proximity detection).

I dont have yet an IPv6 light bulb.  If I had one, it would be behind
that tablet, at a same level as the smartwatchesbands.

In this setting, if one makes the access point to request a few /64
prefixes then it would give some of them to the tablet.  But the tablet
can not - normally - delegate such a /64 prefix any further to the
smartwatchesbands and IPv6 light bulbs.

IF the access point and the tablet begin to delegate such /64 prefixes
beyond what the network topology - a hierarchy - accommodates along its
natural boundaries, then the routing becomes quirky.  By quirky routing
I mean routing that does not map precisely a prefix hierarchy along a
topology hierachy.

To better qualify this description, allow me a comparison: a smartphones
connecting to a cellular network obtains only a /64.  When it wants to
make a local hotspot (aka 'tethering'), it share that /64 with devices
on WiFi rather, which is an operation strange to routing.  This works,
but does not scale to more than one level, and the routing becomes more
quirky, because the prefix hierarchy does not match the topology hierarchy.

To understand why this '64share' does not work beyond one more level,
allow me to make a rhetorical question: has one ever seen a tethering
smartphone connecting and the TV (wifi) _and_ the IPv6 light bulb (BT)?
I think not.  Or, we would like this to be possible, in case the ISP
landline fails.

Alex

  Shouldn't we define the
> SNAC and perhaps other use cases in the draft as well? Currently it 
> is a very high level "prefixes to be distributed into a network to be
> useable" which by itself wouldn't lead to requirement LPD-4.
> 
> Esko
> 
> -----Original Message----- From: v6ops <[e-mail]> On 
> Behalf Of Olorunloba Olopade Sent: Thursday, December 1, 2022 08:48 
> To: Brian E Carpenter <[e-mail]>; Timothy Winters
>  <[e-mail]> Cc: IPv6 Operations <[e-mail]> Subject: Re: 
> [v6ops] Updating RFC 7084 - alternate logic
> 
> I will rather take a /61 (as an example) than multiple /64s.
> 
> The debate is about flat vs tree. SLAAC works with both. I'm not 
> bringing variable length SLAAC into the debate.
> 
> Loba
> 
> -----Original Message----- From: Brian E Carpenter 
> <[e-mail]> Sent: 30 November 2022 19:44 To: 
> Olorunloba Olopade <[e-mail]>; Timothy 
> Winters <[e-mail]> Cc: IPv6 Operations <[e-mail]> 
> Subject: Re: [v6ops] Updating RFC 7084 - alternate logic
> 
> On 01-Dec-22 06:50, Olorunloba Olopade wrote:
>> I agree that both can be made to work. I disagree that the flat 
>> model is easier or better. Maybe some concise points on why you 
>> think the flat model is better/easier?
> 
> What Ole said: In the flat mode a PD client can ask for multiple 
> /64s.
> 
> That keeps everything simple and aligned with the fact that all hosts
> support SLAAC, even if they don't support DHCPv6, and that all SLAAC
> implementations rely on /64 today.
> 
> This would change (and become more complicated) if we standardised 
> variable length SLAAC as Alexandre is suggesting.
> 
> Brian
> 
>> 
>> *From:*Timothy Winters <[e-mail]> *Sent:* 30 November 2022 
>> 17:45 *To:* Olorunloba Olopade <[e-mail]> 
>> *Cc:* Ted Lemon <[e-mail]>; IPv6 Operations 
>> <[e-mail]> *Subject:* Re: [v6ops] Updating RFC 7084 - 
>> alternate logic
>> 
>> Hi Olorunloba,
>> 
>> I'm suggesting that when users have there own gateways, that will 
>> still work with this update.  As Ole mentioned, I think a flat 
>> model is easier than a tree model.
>> 
>> ~Tim
>> 
>> On Wed, Nov 30, 2022 at 12:42 PM Olorunloba Olopade 
>> <[e-mail] 
>> <mailto:[e-mail]>> wrote:
>> 
>> I agree with your general thoughts here – we should fix the spec 
>> where it is wrong. However, I disagree with the specific here that
>>  the spec is clearly wrong.
>> 
>> And I’ve tried to argue from both angles – existing implementation
>>  and right approach.
>> 
>> To re-state my points on right approach
>> 
>> * Resulting tree mirrors topology * Removes limitation on a 
>> specific prefix size * More flexible design
>> 
>> And as per use case, I’ve seen scenarios where our customer doesn’t
>> want to use the ISP CPE (which is allocated the /56). They want to
>> use their own gateway, and might also want to have a separate DMZ
>> for some internal servers. In this scenario, the /64 isn’t
>> adequate.
>> 
>> *From:*Ted Lemon <[e-mail] <mailto:[e-mail]>> 
>> *Sent:* 30 November 2022 16:44 *To:* Olorunloba Olopade 
>> <[e-mail] 
>> <mailto:[e-mail]>> *Cc:* IPv6 Operations 
>> <[e-mail] <mailto:[e-mail]>>; Timothy Winters 
>> <[e-mail] <mailto:[e-mail]>> *Subject:* Re: [v6ops] 
>> Updating RFC 7084 - alternate logic
>> 
>> I think it’s important to be clear on the distinction between what
>>  some spec may require and what will actually work best.  When the
>>  spec is wrong, we should update it. This doesn’t mean every 
>> implementation has to be updated, but if we realize that the spec 
>> is wrong, we should definitely fix it, not live with it forever.
>> 
>> In this case, the spec is clearly wrong: it’s requiring an 
>> allocation strategy that will never in practice be correct. This is
>> why we didn’t adopt this work in the IETF. This was a known issue
>> at the time.
>> 
>> If you have some use case where you think this is the right thing,
>>  then you should argue from that position. Arguing from the 
>> position that we can’t fix a past mistake just doesn’t make sense.
>> 
>> Op wo 30 nov. 2022 om 11:24 schreef Olorunloba Olopade 
>> <loba.olopade=[e-mail] 
>> <mailto:[e-mail]>>
>> 
>> Yes, it is a MUST in the requirements.
>> 
>> I don’t have a large enough pool to conclude how widely it is 
>> implemented. But it is implemented (somewhat) in ALL the CPEs I’ve
>>  come across.
>> 
>> If the issue is the tree, this is a by product of the physical 
>> topology. By avoiding a complex physical topology, we can avoid a 
>> complex tree. Personally, I still prefer the tree as it mirrors the
>> topology and would make troubleshooting easier. I expect that it
>> would be more difficult to troubleshoot with relays.
>> 
>> I also don’t see a problem with under utilised prefixes (something
>>  we generally don’t have a problem with, when it comes to v6). I 
>> see more of a problem where I want something later than a /64, and 
>> I cannot get it. Yes, my scenario for wanting something larger
>> than a /64 is possibly not SNAC related, but this comes under
>> general CE requirements.
>> 
>> *From:*Timothy Winters <[e-mail] <mailto:[e-mail]>> 
>> *Sent:* 30 November 2022 15:56 *To:* Olorunloba Olopade 
>> <[e-mail] 
>> <mailto:[e-mail]>> *Cc:* IPv6 Operations 
>> <[e-mail] <mailto:[e-mail]>> *Subject:* Re: [v6ops] 
>> Updating RFC 7084 - alternate logic
>> 
>> Hi Olorunloba,
>> 
>> I was aware of the requirements, there were a couple of things I 
>> was trying to avoid.   This model creates a tree that can lead to 
>> under utilized prefixes which was somehting I wanted to avoid. 
>> Additionally, I'm aware that it's not widely implemented due to the
>> complexity.   Do you know if all eRouters are required to support
>> this?
>> 
>> ~Tim
>> 
>> On Wed, Nov 30, 2022 at 10:16 AM Olorunloba Olopade 
>> <[e-mail] 
>> <mailto:[e-mail]>> wrote:
>> 
>> Hello,
>> 
>> Wile RFC7084 doesn’t cover the DHCP requirements, there are other 
>> spec (e.g. cablelabs) that does. And we have implementation of 
>> this.
>> 
>> I agree that we should support DHCP on the CE, but don’t support 
>> limiting the sub-delegation to /64, which would make some of the 
>> current implementations non-compliant. I will suggest something 
>> like the following, which is an amendment of the cablelabs spec
>> 
>> • If the Topology mode is set to “favor config”, then divide the 
>> delegated prefix into sizes specified by the CE config.
>> 
>> • If the provisioned MSO assigned IA_PD is smaller than a /56 
>> (e.g., a /60) and the Topology mode is set to "favor depth", the CE
>> MUST divide the delegated prefix on two (2)-bit boundaries into 
>> four (4) sub[1]prefixes by default.
>> 
>> • If the provisioned MSO assigned IA_PD is smaller than a /56 
>> (e.g., a /60) and the Topology mode is set to "favor width", the CE
>> MUST divide the delegated prefix on three (3)-bit boundaries into
>> eight (8) sub[1]prefixes by default.
>> 
>> • If the provisioned MSO assigned IA_PD is a /56 or larger and the
>>  Topology mode is set to "favor depth", the CE MUST divide the 
>> delegated prefix on three (3)-bit boundaries into eight (8) 
>> sub-prefixes by default.
>> 
>> • If the provisioned MSO assigned IA_PD is a /56 or larger and the
>>  Topology mode is set to "favor width", the CE MUST divide the 
>> delegated prefix on four (4)-bit boundaries into sixteen (16) 
>> sub-prefixes by default.
>> 
>> • If the provisioned MSO assigned IA_PD is too small to divide in 
>> the manner described, the CE MUST divide the delegated prefix into
>>  as many /64 sub-prefixes as possible and log an error message 
>> indicating the fault
>> 
>> *From:*v6ops <[e-mail] 
>> <mailto:[e-mail]>> *On Behalf Of *Timothy Winters 
>> *Sent:* 18 November 2022 14:47 *To:* IPv6 Operations 
>> <[e-mail] <mailto:[e-mail]>> *Subject:* [v6ops] 
>> Updating RFC 7084
>> 
>> Hello,
>> 
>> I've started a draft to update RFC 7084 to support prefix 
>> delegation on the LAN interfaces.  The current state of IPv6 in 
>> home networks is ISP are assigning prefixes of appropriate sizes 
>> but they currently are under utilized due to the lack of prefix 
>> delegation on LAN interfaces.
>> 
>> This draft is an attempt to add that support to the draft.
>> 
>> https://datatracker.ietf.org/doc/draft-winters-v6ops-cpe-lan-pd/ 
>> <https://datatracker.ietf.org/doc/draft-winters-v6ops-cpe-lan-pd/>
>> 
>> This is only an update to 7084 at the moment, there has been some 
>> discussion on the snac working group about leveraging this work as
>>  well.
>> 
>> One item being discussed is this currently doesn't solve 
>> multi-homed networks.
>> 
>> I welcome any feedback about the proposal.
>> 
>> ~Tim
>> 
>> 
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