Re: [v6ops] Updating RFC 7084 - alternate logic

[Olorunloba Olopade <[e-mail]>]

Being more correct does not make it better though. If precise allocation was the prime objective, then there is a fundamental flaw in assigning a /56 or /48 to the CE in the first place. Isn’t it best practice in address planning to leave room for future growth?

Being flat, we cannot summarise the prefixes. It means there is an attack vector in that someone could generate a lot of routes on the router (65K if ISP assigned size is /48).

Loba

From: Ted Lemon <[e-mail]>
Sent: 30 November 2022 17:53
To: Olorunloba Olopade <[e-mail]>
Cc: Timothy Winters <[e-mail]>; IPv6 Operations <[e-mail]>
Subject: Re: [v6ops] Updating RFC 7084 - alternate logic

The flat model is more correct, not easier. It's more correct in the sense that we assign one prefix to every link that needs one, rather than arbitrarily assigning prefixes to routers, which may or may not need to sub-delegate.

It is, however, not much harder. It requires that routers that support sub-delegation support the use of relay agents, and that when they relay a sub-delegated prefix, they also route it. They already have to route prefixes that they sub-delegate—what's different is that it's the DHCP relay doing it, rather than the DHCP server.

On Wed, Nov 30, 2022 at 12:50 PM Olorunloba Olopade <[e-mail]<mailto:[e-mail]>> 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?

From: Timothy Winters <[e-mail]<mailto:[e-mail]>>
Sent: 30 November 2022 17:45
To: Olorunloba Olopade <[e-mail]<mailto:[e-mail]>>
Cc: Ted Lemon <[e-mail]<mailto:[e-mail]>>; IPv6 Operations <[e-mail]<mailto:[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/

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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