Re: [Roll] [roll] #90: use of transient instance ID

"Pascal Thubert (pthubert)" <> Thu, 12 April 2012 06:14 UTC

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Date: Thu, 12 Apr 2012 08:13:14 +0200
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Thread-Topic: [Roll] [roll] #90: use of transient instance ID
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From: "Pascal Thubert (pthubert)" <>
To: Mukul Goyal <>
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Subject: Re: [Roll] [roll] #90: use of transient instance ID
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Hi Mukul

Don't worry! For the upper layers interaction I'm only asking for one sentence, not an API spec... Like:
"The required lifetime for the routing states may be provided by the application via a hint from upper-layer protocols. Additional hints from upper-layer protocols can be used to tear down the remaining states at the origin and/or at the target as soon the application need of those states is terminated or the application detects that the states are not functional anymore. In a same fashion, an interaction with upper layers can be used to determine that the routing states are still valid and can be prolonged for an additional lifetime"

That's all!

For your questions please see inline. Also, as an example of existing art, RFC 4861 stays as abstract as I do above with text like:

      DELAY       The neighbor is no longer known to be reachable, and
                  traffic has recently been sent to the neighbor.
                  Rather than probe the neighbor immediately, however,
                  delay sending probes for a short while in order to
                  give upper-layer protocols a chance to provide
                  reachability confirmation.


7.3.1. Reachability Confirmation

   A neighbor is considered reachable if the node has recently received
   a confirmation that packets sent recently to the neighbor were
   received by its IP layer.  Positive confirmation can be gathered in
   two ways: hints from upper-layer protocols that indicate a connection
   is making "forward progress", or receipt of a Neighbor Advertisement
   message that is a response to a Neighbor Solicitation message.


-----Original Message-----

[Pascal] Also, when there are no routing states in intermediate routers, an indication from upper layers can be used in the end points to consider that all states for an instanceID are now cleaned up.

[Mukul] Not sure what you mean. 

[Pascal2] Let me reword:  if HbH routin gis not used, the only states with any persistence are on the origin and target(s). The upper layer protocol (ULP) in origin and target may know when they are done with their need for the routes. If they are done before (config option) lifetime is up, they can tear down the states. This requires a new cross layer interaction triggered by ULP, similar to IPv6 ND in DELAY state.

You think P2P-RPL needs to define this cross-layer interaction? This is simply the upper layer telling the network layer to chuck a source route. Isn't it? The upper/lower layers dont even need to remember that this route was discovered using P2P-RPL. Also, the origin (or the target) can use a source route as long as it wants. Why should the lifetime in config option dictate how long this route can be used?

[Pascal3] In IPv6, by design, everything has a lifetime. Better fix this now than during IESG review. In the case of this draft, nodes commit resources which are by definition limited. Thus in the general case that the draft addresses they can't commit those resources forever. One end point might die, say out of battery. There must be something that in any case will ensure that all parties, end points and intermediate routers in HbH end up clean even if there is no (rst) signaling to achieve so. 

You can pick a large lifetime if you like for the light switch you have in mind; but there needs to be a lifetime, after which states must be revalidated. That can be rebuilding the DAG, this can be unicast like a ping, and this can by piggy backed with traffic. ND for instance uses upper layer hints to validate that the reachability without necessarily signaling everything. Since you are going for experimental, I'm asking for the bare minimum, a simple lifetime using existing means (the config option). 

 If an application is responsible for setting up routing states, this application may also be clever enough to provide a hint on the lifetime, and to tear down the states that it caused when it does not need them anymore. If the application does not provide any hint whatsoever, the implementation at the origin will select a reasonable lifetime that will depend on the function of the object. I'm certainly not asking to define the interaction between upper layer and L3, this is internal and thus implementation.



----- Original Message -----
From: "Pascal Thubert (pthubert)" <>
To: "Mukul Goyal" <>,
Sent: Tuesday, April 10, 2012 4:52:50 AM
Subject: RE: [Roll] [roll] #90: use of transient instance ID


I meant a suggestion, not a capitalized word. I prefer the suggestion but I'm still OK with your proposal. If we get in agreement on the lifetime of the states (issue #85), then you can indicate that lifetime is one way to determine when all stale states can be considered gone. Also, when there are no routing states in intermediate routers, an indication from upper layers can be used in the end points to consider that all states for an instanceID are now cleaned up.



-----Original Message-----
From: [] On Behalf Of Mukul Goyal
Sent: dimanche 8 avril 2012 18:09
Subject: Re: [Roll] [roll] #90: use of transient instance ID

Hi Pascal

Re-read your proposed resolution text. I am not sure that the draft should suggest rotating the instance ids. My proposed resolution is to simply suggest not using instance id that might be in use.

" [Mukul2] Makes sense. I think it is sufficient to caution (with a SHOULD
 NOT) against reusing instance ids for which the stale state might exist  in the nodes."


----- Original Message -----
From: "roll issue tracker" <>
To: mukul@UWM.EDU,
Sent: Wednesday, April 4, 2012 8:11:44 AM
Subject: [roll] #90: use of transient instance ID

#90: use of transient instance ID

 Problem (resolution agreed upon)
 P2P creates temporary states in the transient DAG with a transient  instance ID. The protocol must ensure that if the instance ID is reused  then the new operation it is not confused with states resulting from the  previous use of the same instance ID. Suggestion is to propose a  rotation.


 "RPLInstanceID: RPLInstanceID MUST be a local value as described in  Section 5.1 of [I-D.ietf-roll-rpl]. The origin MUST NOT use the same  RPLInstanceID in two or more concurrent route discoveries."

 I'd suggest that you enforce a round robin or an opaque circulation so  that the new instanceID is the least recently used one out of the 64  possible.

 I think we should leave it to the origin to decide which value it wants  to use for RPLInstanceID. I know some implementations are planning to  use a fixed RPLInstanceID value for all route discoveries.

 [Pascal2] Changing the instance ID will help debug the network and avoid  conflicts with stale states. What's really up to the device is the  initial sequence. Leaving it up to the origin may help the origin defeat  some attacks to some degree. OTOH, after all the instances have been  played, LRU forces to replay the same sequence again so the shield  drops. My preferred approach would be a SHOULD that would say that the  next instance ID SHOULD NOT be one of the (16?) most recently used and  MUST NOT be one for which states might still exist in the network. IOW  either the states deletion was acknowledged, or all pending lifetimes  are exhausted.

 [Mukul2] Makes sense. I think it is sufficient to caution (with a SHOULD
 NOT) against reusing instance ids for which the stale state might exist  in the nodes. Using a "MUST NOT" may not be OK since a node may never be  100% sure about non-existence of stale state with a particular instance  id (thus, all possible instance id values will become suspect and hence  unusable after a while).

 [Pascal3] Agreed. Note that a circulation is a bonus to defeat replays.
 And now we're back to the issue above. How does the device know that  there is no state left? A lifetime definition would be very useful. That  lifetime is different from the DAG's one in RDO. I think we have an open  issue here.

 [Mukul3] As I mentioned above, the life time parameters inside the DODAG  configuration option specify the life time of the hop-by-hop routing  state for the routes discovered using P2P-RPL.

 [Pascal4] This boils down to the thread above. Only one issue really,  which lifetime is which? So IMHO no need to log anything for this  thread.

 [Mukul4] OK.


 Reporter:  jpv@…                  |      Owner:  mukul@…
     Type:  defect                 |     Status:  new
 Priority:  major                  |  Milestone:
Component:  p2p-rpl                |    Version:
 Severity:  Submitted WG Document  |   Keywords:

Ticket URL: <>
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