Hello Tony

I agree that 0 is default, this helps for backward compatibility as well.
Note that the field is not the TID (T is for transaction). I’m proposing to add 
a new Opaque field since what is carried is opaque to ND.
New text would say:

       A new Opaque field is introduced to carry opaque information in case the
       registration is relayed to another process, e.g.; injected in a routing
       protocol.
       A new "I" field provides an abstract type for the opaque information, and
       from which the 6LN derives to which other process the opaque is expected
       to be passed.
       A value of Zero for I indicates an abstract topological information to
       be passed to a routing process if the registration is redistributed.
       In that case, a value of Zero for the Opaque field is backward-compatible
       with the reserved fields that are overloaded, and the meaning is to use
       the default topology.

8  bits is what’s left in the option that we need to keep backwards compatible.

   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |     Type      |     Length    |    Status     |    Opaque     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |  Rsvd | I |R|T|     TID       |     Registration Lifetime     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
...             Registration Ownership Verifier                 ...
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

What do you think?

Pascal

From: Tony Przygienda <tonysi...@gmail.com>
Sent: jeudi 12 avril 2018 17:43
To: Pascal Thubert (pthubert) <pthub...@cisco.com>
Cc: 6lo@ietf.org; Yan Filyurin <yanf...@gmail.com>; 
draft-ietf-6lo-rfc6775-upd...@ietf.org; r...@ietf.org
Subject: Re: instance ID in rfc6775 update

Yes, we do have discussions over RIFT where it seems a multi-plane or if you 
want multi-topology concept as introduced originally in RFC5120 would be 
helpful. RIFT can be very easily instantiated on multiple ports and with that 
has no problem to run multi-instance/topology but the dataplane correlation 
from the leaf would be very helpful. RIFT leaf implementation is very "thin" 
and with that architectures that don't rely on either LOC-ID or BGP overlays 
become feasible, albeit obviously not @ the scale something like 2547bis or 
EVPN can operate.
So in short, I think I support this suggestion fully.

For the practical encoding, I suggest to choose TID=0 as "default topology", 
i.e. "what you do today" and avoid an I bit which will cause an encoding corner 
case if it's not set but TID<>0?
From experience, 8 bits is just about enough but 12 bits are plenty for # of 
topologies people sometimes think they need on building network architectures 
...

my 2c ...

--- tony

On Thu, Apr 12, 2018 at 7:23 AM, Pascal Thubert (pthubert) 
<pthub...@cisco.com<mailto:pthub...@cisco.com>> wrote:
Hi again

A proposed text would be like:


   0                   1                   2                   3
   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |     Type      |     Length    |    Status     |    Opaque     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |  Rsvd | I |R|T|     TID       |     Registration Lifetime     |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                                                               |
...             Registration Ownership Verifier                 ...
  |                                                               |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

….

Opaque:
       One-byte Opaque field; this is an octet that ND does not need to process
       but that the 6LN wishes the 6LR to pass transparently to another process.
I:
       Two-bit Integer: A value of zero indicates that the Opaque field carries
       an abstract index that is used to decide in which routing topology the
       address is expected to be injected. In that case, the Opaque field is
       passed to a routing process with the indication that this is a topology
       information and the value of 0 indicates default. All other values are
       reserved.


Does that work?

Pascal

From: Pascal Thubert (pthubert)
Sent: jeudi 12 avril 2018 15:40
To: 6lo@ietf.org<mailto:6lo@ietf.org>
Cc: Yan Filyurin <yanf...@gmail.com<mailto:yanf...@gmail.com>>; Tony Przygienda 
<tonysi...@gmail.com<mailto:tonysi...@gmail.com>>; 
draft-ietf-6lo-rfc6775-upd...@ietf.org<mailto:draft-ietf-6lo-rfc6775-upd...@ietf.org>
Subject: instance ID in rfc6775 update

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

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