[6lo] instance ID in rfc6775 update

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

Dear all :

During a conversation on the RIFT protocol it appeared that there are use cases in RIFT to support host mobility with rfc6775-update.
There is a caveat, though, which is in fact common with RPL. Both cases need a concept of multi topology routing.
In the case of RPL, the topology is indexed by an instance ID. In the case of RIFT, there is a need for an index to a RIB, so one octet is probably enough.
A suggestion is thus to use the reserved octet in the ARO to carry an instance ID, and use a bit to signal that this is what that field does, in case there is a need later to overload it with something else.

I understand this is coming late in the process; but then there is no logic associated to the change, this is just passing on an additional information that is useful for more than one candidate protocol.

Please let me know if there is an issue pursuing this. If there is no opposition, my plan it currently to add this in rev-19.

All the best,

Pascal