Re: [Pce] Urgent issue with draft-ietf-pce-stateful-pce : PCE advising PCC about no path

[Dhruv Dhody <[e-mail]>]

Hi Stephane,

The case you described is valid and important to support. I am one of those who believed empty ERO to be just fine, but I understand the other point of view as well.
IMHO we need to resolve it quickly and completely.  I see two ways -

(1) Allow Empty ERO to mean no path.
Let it be valid in all messages to mean that no intended path exists for this LSP.
As per -16,
- empty ERO is added in the end of synchronization marker (PCRpt).
- The ERO may be empty if the PCE does not have a path for a delegated LSP.

We can add text in section 6.2 to say something like -

The ERO may be empty if the PCE does not have an intended path for the delegated LSP.
If the local policy allows it, the PCC SHOULD signal the tear down of the LSP. At
this time, PCC MAY also revoke delegation and use a locally computed path instead.

To me this is more logical and in spirit with the rest of the document, also would require least amount of changes in existing implementations.

(2) Add NO-PATH object
If we do this way, then we need to make following changes in all messages!


-        Remove ERO as mandatory object and its error codes in all messages

-        Change RBNF to add NO-PATH object

-        Update NI fields (if needed)

All existing implementation would need change, and this change would be a non-backward-compatible change. This is what I am afraid of the most especially with open source. But if this is the only way to reach consensus and move the document forward, I *personally* could live with it.

Hi Harish

I agree with Stephane we have returning/revoking of delegation as the right mechanism for PCC to select the locally computed path instead.
Do you have suggestion to improve the text above if we go with option 1?

Regards,
Dhruv


From: Pce [mailto:[e-mail]] On Behalf Of [e-mail]
Sent: 03 October 2016 13:58
To: Harish Magganmane <[e-mail]>; Aissaoui, Mustapha (Nokia - CA) <[e-mail]>; [e-mail]; [e-mail]
Subject: Re: [Pce] Urgent issue with draft-ietf-pce-stateful-pce : PCE advising PCC about no path

Hi Harish,

Thanks for your feedback.
I do not really understand why you map the empty ERO to a decision to possibly fallback computation to local.
As you mentioned, it could be a local PCC policy decision and this local policy could be to tear down the LSP instead of deferring ERO selection to the local router as you proposed.

The important point is the semantic of this empty ERO, not really the action taken. I understand in your email  that you still interpret it from a semantic point of view has an indication of no path, so you then can decide to defer ERO selection to the router. Because in the case, you want to have the PCE giving back path computation role to PCC, the PCE must use the delegate flag for this purpose and can revoke the delegation at anytime. I'm trying to understand what you really want to achieve here. Or do you want to have PCE updating LSP parameters/constraints but let the PCC compute path ?

Best Regards,

Stephane



From: Harish Magganmane [mailto:[e-mail]]
Sent: Saturday, October 01, 2016 00:53
To: LITKOWSKI Stephane OBS/OINIS; Aissaoui, Mustapha (Nokia - CA); [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: Re: [Pce] Urgent issue with draft-ietf-pce-stateful-pce : PCE advising PCC about no path

Hi Stephane,

We are not in favor of using empty ERO as way to signal the tearing of an LSP. IMO empty ERO object should be interpreted to mean deferring the ERO selection to the router, perhaps through local policy on the PCC. For example PCC could choose between a local CSPF or a IGP based hop-by-hop.

In cases where we want PCE to explicitly control the behavior of the PCC when a path is not available, NO-PATH object can be used to dictate the behavior. One such behavior could be that of tearing down the LSP.

Thanks,
Harish

From: Pce <[e-mail]<mailto:[e-mail]>> on behalf of "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Date: Friday, September 30, 2016 at 8:33 AM
To: "Aissaoui, Mustapha (Nokia - CA)" <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>, "[e-mail]<mailto:[e-mail]>" <[e-mail]<mailto:[e-mail]>>
Subject: Re: [Pce] Urgent issue with draft-ietf-pce-stateful-pce : PCE advising PCC about no path

Hi Mustapha,

Your proposal works from my point of view, but it looks that it causes some trouble to another vendor so I would like these people (and others as well) to express their concerns regarding usage of empty ERO.

Thanks for pointing again your last proposal.

Best Regards,

Stephane


From: Aissaoui, Mustapha (Nokia - CA) [mailto:[e-mail]]
Sent: Friday, September 30, 2016 17:08
To: LITKOWSKI Stephane OBS/OINIS; [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: RE: Urgent issue with draft-ietf-pce-stateful-pce : PCE advising PCC about no path

Hi Stephane,
In the last email related to this issue, I made a proposal to Olivier and Robert commented on it. Would that be sufficient to address this interop issue?
https://mailarchive.ietf.org/arch/msg/pce/A1ADiw6Uvjn1ETjErqzgjdjXnsE

Mustapha.

From: Pce [mailto:[e-mail]] On Behalf Of [e-mail]<mailto:[e-mail]>
Sent: Friday, September 30, 2016 5:46 AM
To: [e-mail]<mailto:[e-mail]>; [e-mail]<mailto:[e-mail]>
Subject: [Pce] Urgent issue with draft-ietf-pce-stateful-pce : PCE advising PCC about no path

Hi WG, and draft authors,

We still have an urgent interoperability issue to solve with draft-ietf-pce-stateful-pce. We currently have no clear semantic for the PCE to advise the PCC that there is no more path available. This point was already raised through the list but as we need an URGENT resolution of this issue because of implementation timelines, I would like to reactivate the thread.

The situation of no path at PCE side can happen in many situations, and a particular situation will require PCC to tear down an existing path : let's think about two strictly SRLG disjoint LSPs with a working path . Now the transmission topology is changing (rerouting at WDM layer) leading SRLG disjointness not being fitted anymore and PCE cannot find anymore disjoint path, it must advise one PCC to tear down the path because it is no more disjoint (strict disjointness required).
We do not have any clear semantic today and some implementations are using empty ERO for this purpose in PCUpdate but the PCC does not recognize it as a valid no path significance.

This subject is critical and I would like that we can achieve a consensus asap on the target solution so then vendors can align implementations.
This thread is focusing on the PCE -> PCC way, but having a semantic of reporting a no path is also necessary in PCC->PCE way through PCRpt, at least to ACK a PCupdate.

One of the previous discussion on the list talked about the possibility to use NO-PATH object which already has this semantic for PCReq/PCRep but as already mentioned we need to assess impact on existing implementations, so vendor feedback (with customer implementations) is highly required. So this is my starting proposal to initiate the discussion.


Best Regards,


[Orange logo]<http://www.orange.com/>

Stephane Litkowski
Network Architect
Orange/SCE/EQUANT/OINIS/NET
Orange Expert Future Networks
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