Re: [6lo] BBR versus rfc6775-update document

["Pascal Thubert (pthubert)" <[e-mail]>]

I agree with Charlie below but maybe for non-blocking tiny details.

The bottom line is that RFC 6775 update defines the interface that the 6LN will use to get routing services. This interface was initially designed for the sole use of the 6BBR spec. As it goes it is good enough to get routing services from RPL (https://tools.ietf.org/html/draft-thubert-roll-unaware-leaves) and RIFT (https://tools.ietf.org/html/draft-ietf-rift-rift) so the pointer to the 6BBR should be maintained but generalized.

This is why the change is mostly to define the routing proxy, indicate that the 6BBR is a routing proxy, and in a number of places change 6BBR to routing proxy.

The tiny details that we still need to agree upon are places like fig4 where the flow all the way to the 6BBR is shown. It is not needed for this spec. Everything on the right could be abstracted to the work by either the 6LR, or the routing proxy if the 6LN attaches directly to the routing proxy. I still liked to maintain that picture, to help the reader that does not need/want to look at the BBR spec to get a glance at the big picture in the specific case of the 6BBR. I’d like to hear other voice(s).

Please see below:

From: Charlie Perkins <[e-mail]>
Sent: jeudi 7 juin 2018 23:30
To: [e-mail]
Cc: Pascal Thubert (pthubert) <[e-mail]>; Suresh Krishnan <[e-mail]>
Subject: Re: [6lo] BBR versus rfc6775-update document


Hello folks,

After a long discussion with Pascal about the proposed changes, we came to be much closer in our outlook on the material that is needed in 6775bis (i.e., draft-ietf-6lo-rfc6775-update).  The least confusing and most straightforward way I can summarize the results is to revise my earlier email.

In 6775bis, we can define something called a "routing registrar" as a feature-rich node that is both a registrar and provides Internet reachability for the LLN multilink subnet.  The intention in 6775bis is, then, to specify registration signaling to meet the needs that are identified for such a routing registrar.  The BBR document, on the other hand, is intended to specify a particular kind of routing registrar, which is to be called a 6BBR.

My understanding is that this has actually been mostly the intention, especially given the opportunity to develop 6775bis and the BBR document in parallel.  The documents are intended to work well together (and also with the AP-ND document).  Yet it is also intended to have a clear separation between what the 6LNs, 6LRs, and 6LBRs expect from a routing registrar, versus the mandates and specification details as needed for the kind of routing registrar known as a 6BBR.

The intention is still to submit revision draft-ietf-6lo-rfc6775-update-21.txt by early next week.

On 6/6/2018 11:10 PM, Charlie Perkins wrote:

Hello folks,

I still think it would be a significant improvement to refactor the specification of the 6BBR mandates to live entirely within draft-ietf-6lo-backbone-router (BBR).  For that reason, I have prepared a summary of the changes to draft-ietf-6lo-rfc6775-update (6775bis) that would be required.  I left out a few occurrences of the term 6BBR that could obviously be deleted.

Citations of I-D.ietf-6lo-backbone-router that might be taken to represent normative references would be deleted.




   o  Registration via an IPv6 ND proxy over a Backbone Link (6BBR)


This bullet point would fit well in BBR and does not need to be in 6775bis.

Better to retain the bullet and reword as follows:

  *   Registration to an IPv6 ND proxy

[PT>] This become registration to a routing registrar, of which 6BBR doing IPv6 ND proxy is an example.




   Backbone Router (6BBR):  A logical network function in an IPv6 router
         that proxies the 6LoWPAN ND operations specified in this
         document to assure address uniqueness and other functions
         required so that multiple LLNs can operate as a single IPv6
         network.


This definition will be reworked as needed for the idea of routing registrar.

[PT>] Not sure we need to rework it much. We can define the routing registrar above and here just add that the 6BBR is a routing registrar.





                                                                   In a
         Route-Over network, a 6LBR may register the 6LN to the 6BBR.



This sentence should be deleted from 6775bis definition for "Registration", regardless of BBR.

The operation is described elsewhere and doesn't belong in the definition.




   |   5   | Validation Requested: The Registering Node is challenged  |
   |       | for owning the Registered Address or for being an         |
   |       | acceptable proxy for the registration.  A registrar (6LR, |
   |       | 6LBR, 6BBR) MAY place this Status in asynchronous DAC or  |
   |       | NA messages.                                              |



Here, the list of registrars does not need to include 6BBR, and the BBR document would simply add 6BBR as a registrar.  By the way, "registrar" is an undefined term in 6775bis, and it does merit a definition.

Definitions for "registrar" and "routing registrar" will be provided.  The last sentence will make it clear that the list of example registrars is not intended to be exclusive of other possibilities.




   The new "L", "B", and "P" flags, indicate whether a router is capable
   of acting as 6LR, 6LBR, and 6BBR, respectively.  These flags are not
   mutually exclusive; an updated node can advertise multiple collocated
   functions.



Logically speaking, "L" and "B" should be defined in 6775bis, and "P" should be defined in BBR.

The "P" flag will be redefined to signal the presence of a routing registrar, and retained in 6775bis.




                     Figure 4: (Re-)Registration Flow


Figure 4 in 6775bis should be modified so that the proxy NS and proxy NA are not shown in 6775bis, but the current Figure 4 should be situated within the BBR document with explanations about the proxy messages and NS(DAD) operation.

The revised figure 4 in 6775bis will attempt to clarify the above architectural considerations.  The Figure 4 currently in 6775bis will be introduced into the BBR document; it is already specialized to the case of 6BBRs.


[PT>] I still like to show the overall flow for a real 6BBR as is there for information. But the doc lives well without it.




Old in 6775bis:
   o  The Target Address in the NS containing the EARO is now the field
      that indicates the address that is being registered, as opposed to
      the Source Address field as specified in [RFC6775] (see
      Section 5.5).  This change enables a 6LBR to use one of its
      addresses as source of the proxy-registration of an address that
      belongs to a LLN Node to a 6BBR.  This change also avoids in most
      cases the use of an address as source address before it is
      registered.



New in 6775bis:
   o  The Target Address in the NS containing the EARO is now the field
      that indicates the address that is being registered, as opposed to
      the Source Address field as specified in [RFC6775] (see
      Section 5.5).   This change enables a 6LBR to proxy the registration
      of an address that belongs to a 6LN to a routing registrar, and also
      avoids in most cases the use of an address as source
      address before it is registered.




------------------------------  continuing  ------------------
   The Registering Node is the node that performs the registration to
   the 6BBR.  As in [RFC6775], it may be the Registered Node as well ...


If there are multiple 6LRs in the routing path from 6LN to 6LBR, I don't think this statement is completely accurate.  It would be accurate if the words "to the 6BBR" were omitted.

Here, "6BBR" can be replaced by "routing registrar".  I still have a concern about disallowing other kinds of registrations, though.  More later.


[PT>] I agree you point on something valid here and that it should not be about disallowing. It is about the distinction between the node that performs the registration and the node for whom it is performed. In the full 6BBR flow, with all the components, 6LN, 6LR, 6LBR and 6BBR involved,  the 6LBR is the registering node in the registration to the 6BBR, and the 6LN is the registered node. We can avoid the “6BBR” if we make the text very crisp when there are 2 registrations in the same flow, one 6LN to the 6LR at the edge, and one 6LBR to 6BBR at the root.
This can be very confusing and is where fig 4 as it stands now becomes very useful.


                             In that case, if the Registered Node is reachable from the
   6BBR over a Mesh-Under mesh, the Registering Node indicates the MAC
   Address of the Registered Node as the SLLA in the NS(EARO).

and
  This enables the Registering Node to attract the packets from
   the 6BBR and route them over the LLN to the Registered Node.


Here, "6BBR" can be replaced by "routing registrar".




                       As described in [I-D.ietf-6lo-backbone-router], the
   "Moved" status can be used by a 6BBR in an NA(EARO) message to
   indicate that the ownership of the proxy state on the Backbone Link
   was transferred to another 6BBR as the consequence of a movement of
   the device.



Within 6775bis it should be made clear that the registration procedure is being enhanced to enable mobility, and that the routing registrars have a crucial role to play.


[PT>] yes, isn’t that done yet? We mention it even in the abstract, and serve requirements in appendix B1.




   The LLN nodes depend on the 6LBR and the 6BBR for their operation.



This statement cannot be true in networks that don't have any 6BBRs.  And, it's not exactly true in LLNs that have peer-to-peer routing, either.  In any case, a modified version deleting 6BBR is pretty much true (i.e., a lot "more true") and depicts the security point just as well.

The statement could be replaced by "The LLN nodes depend on a 6LBR and may need the services of a routing registrar for their operation."


[PT>] WFM


   This specification can be used by any wireless node to associate at
   Layer-3 with a 6BBR and register its IPv6 addresses to obtain routing
   services including proxy-ND operations over a Backbone Link,
   effectively providing a solution to the requirements expressed in
   Appendix B.4.




This will be reworded to be aligned with the abovementioned passages.

[PT>] Then again, I’d like to 1) generalize as you indicate and still maintain the text above as an example.
For instance, likewise:
   This specification can be used by any wireless node to register its IPv6
    addresses with a routing registrar to obtain routing services
    such as proxy-ND operations over a Backbone Link by a 6BBR,
     effectively providing a solution to the requirements expressed in
   Appendix B.4.

[PT>] all the best,
Pascal