Old values in new Tables - how to address them

[inesrob]

This ticket came as result of interim meeting in Sep 2023

Link: https://www.youtube.com/watch?v=vOKsz-kSIUA

Time: starting at 31:49 min to 35:40 min

Followup: Rahul will follow up on this topic

Summary: How do we identify old values of mopex in the new tables? optional features mandatory when the old mode is operated as a new mode?

[dbarthel-ol]

Here is the text in -07: "The MOPex option should also be used for existing MOP values 0-6. The use of current MOPs (values 0 to 6) in MOPex indicates that the MOP might be supported with an extended set of semantics e.g., the capability options [I-D.ietf-roll-capabilities]."

My questions:

• I fail to understand "might be supported". If a value appears in the MOPEX field, it tells all RPL nodes that the root has decided to operate in this mode. There is no notion of "supported" in that.
• "might ... with an extended set of semantics e.g.,": I think we need a specification here. Does a value 0 to 6 in MOPEX tell that the network operates exactly the same way as if that value appeared in MOP (with no MOPEX)? If not, where are the differences between MOP==x and MOPEX==x (for x in 0..6) specified?
• as a first conservative measure, in order to avoid creating a mess for the future, I suggest the values 0..6 in the IANA table for MOPEX be assigned names that are different from the names in the MOP table. E.g. : "Augmented Storing Mode" vs. "Storing Mode", etc. It buys us time to decide later what to specify for each of them (some might end up being identical to the corresponding old mode).

[dbarthel-ol]

During the ROLL session at IETF118, it was agreed to create an entry in the MOPEX field for the existing values of MOP (0 to 6), and declare them RESERVED-oldmode-v2, where oldmode is no_downward, non_storing, storing_no_multicast, storing_multicast, P2P, ... Or possibly name them RESERVED-MOPn-v2, where n is 0 to 6. This is meant to hint that, when MOPEX contains the values 0 to 6, the network mode of operation will be the same as with MOP containing the same value, albeit with some options being mandatory to support. These mandates are not written yet, hence the exact behavior cannot be specified as this time. However, we don't want to give an impression that old MOP values in the MOPEX field can be used to specify radically different modes of operations compared to the old modes.