Re: [Pce] Whither Stateless PCE?

Julien Meuric Fri, 12 Aug 2016 02:31:45 -0700

Hi Ina, hi Stéphane,

I am glad to see this discussion progressing, sorry for interrupting.

RFC 5440 defines the END-POINTS object, which includes an egress ID. Do not you think it could be considered to unambiguously convey the egress destination-attached ID in the PCRpt, without colliding with the loose ERO case?

Cheers,

Julien

Aug. 12, 2016 - <stephane.litkow...@orange.com:

Hi Ina,

%%% The PCC must at the minimum know what the destination is, and a loose hop is a way to encode this. I cannot think of any situation in which the PCC does not know the destination. I don't think the PCE should worry about whether the PCC will request a path or not, since we are mandating a PCReq to request a path, the PCE does not have to imply it from the ERO

[SLI] PCC knows the destination but when LSP is delegated, PCC does not own path of the LSP anymore, so ERO should reflect what PCE sent to PCC. Again in case of no path available from PCE, PCE will send empty ERO, PCE will not really understand if PCC reports back an ERO with the destination in the ERO as loose hop as this may imply that the PCC is trying to establish a path to the destination using loose hop which is not compliant with what PCE tells. You may fall into PCUpd/PCRpt loop in such scenario because PCE will try to update PCC until PCC reports the same path as PCE sent in ERO.

Best Regards,

Stephane

From: Ina Minei [mailto:inami...@google.com]
Sent: Thursday, August 11, 2016 19:25
To: LITKOWSKI Stephane OBS/OINIS
Cc: Fatai Zhang; DUGEON Olivier IMT/OLN; Aissaoui, Mustapha (Nokia - CA); adr...@olddog.co.uk; Dhruv Dhody; pce@ietf.org
Subject: Re: [Pce] Whither Stateless PCE?
Stephane,

Please see inline %%%
[snip]

Example :

Case#1 : PCC has no path, it reports empty ERO in PCRpt (case Olivier was mentioning), PCE vendor does not compute path and does not send update

### In this case, the ERO must at least have one loose hop, the destination. This will be clarified in the next version of the draft in (the new) section 6.1. See proposed text below:

The intended path, represented by the ERO object, is REQUIRED. If

the ERO ojbect is missing, the receiving PCE MUST send a PCErr

message with Error-type=6 (Mandatory Object missing) and Error-value

to be assigned by IANA (ERO object missing). When present, the ERO

object SHOULD contain at least one subobject, representing the

destination of the LSP. "

This is a SHOULD and not a MUST because an empty ERO is allowed for

the end of synchronization marker.

[SLI] Having PCC sending an ERO with the destination as loose hop does not make sense to me while PCC has no path. How do you differentiate with the case the PCC reports a loose path to the destination from the case it has no path ?

%%% The PCC must at the minimum know what the destination is, and a loose hop is a way to encode this. I cannot think of any situation in which the PCC does not know the destination. I don't think the PCE should worry about whether the PCC will request a path or not, since we are mandating a PCReq to request a path, the PCE does not have to imply it from the ERO.

ð Using PCReq could make sense here as Mustapha proposed or clearly mentioning that PCRpt with empty ERO needs to trigger path computation and sending PCUpd.

### This will be clarified in the next version of the draft as well, the mode of operation is to mandate a PCReq before the delegation.

[SLI] Ok thanks, that’s the good way to go.

Proposed text (new section 5.8.2)

5.8.2. Switching from Passive Stateful to Active Stateful

This section deals with the scenario of an LSP transitioning from a
passive stateful to an active stateful mode of operation. When the
LSP has no working path, prior to delegating the LSP, the PCC MUST
first use the procedure defined in Section 5.8.1 to request the
initial path from the PCE. This is required because the action of
delegating the LSP to a PCE using a PCRpt message is not an explicit
request to the PCE to compute a path for the LSP. The only explicit
way for a PCC to request a path from PCE is to send a PCReq message.
The PCRpt message MUST NOT be used by the PCC to attempt to request a path from the PCE.
When the LSP is delegated after its setup, it may be useful for the
PCC to communicate to the PCE the locally configured intended
configuration parameters, so that the PCE may reuse them in its
computations. Such parameters MAY be acquired through an out of band
channel, or MAY be communicated in the PCRpt message delegating the
LSPs, by including them as part of the intented-attribute-list as
explained in Section 6.1. An implementation MAY allow policies on
the PCC to determine the configuration parameters to be sent to the
PCE.
(the intended-attribute-list is new, see more below).

Case#2 : PCC has a path, it reports ERO, PCE has different constraints configured, we expect PCE to update the path

Case#3 : PCC has a path, it reports ERO, PCE has a different optimization algorithm leading to a different ERO with the same constraint, we expect PCE to update the path

Case#2 and Case#3 requires the PCE to know the existing constraint configured on PCC for the LSP , by using only PCRpt we cannot have such constraint information, we need a PCReq also to describe the configuration (PCRpt only describes operation state => Mustapha’s point again).

### This observation is correct, the PCRpt currently carries the actual state.

As Robert mentioned in his reply to this thread, the issue you are raising is the one of intended versus actual state.

After discussing at the IETF with Julien, Dhruv, Mustapha as well as offline with other implementors, the proposed solution is to include both the configured (intended) and actual state in the PCRpt.

The following text is proposed to section 6.1

The format of the PCRpt message is as follows:

<PCRpt Message> ::= <Common Header>

<state-report-list>

Where:

<state-report-list> ::= <state-report>[<state-report-list>]

<state-report> ::= [<SRP>]

<LSP>

<path>

Where:

<path>::= <intended_path>

[<actual_attribute_list><actual_path>]

<intended_attribute_list>

[SLI] Why do you interleave intended and actual parameters ? Why not having :

<path>::= <intended_path>

<intended_attribute_list>

[<actual_path><actual_attribute_list>]

%%% This was done in order to keep the encoding backwards compatible with existing implementations
<actual_attribute-list>::=[<BANDWIDTH>]

[<metric-list>]

Where:

<intended_path> is represented by the ERO object defined in

section 7.9 of [RFC5440].

<actual_attribute_list> consists of the actual computed and signaled values

of the <BANDWIDTH> and <metric-lists> objects defined in [RFC5440].

<actual_path> is represented by the RRO object defined in

section 7.10 of [RFC5440].

<intended_attribute_list> is the attribute-list defined in

section 6.5 of [RFC5440] and extended by PCEP extensions.

The intended_attribute_list maps to the attribute_list in Section 6.5

of [RFC5440] and is used to convey the requested parameters of the

LSP path. This is needed in order to support the switch from passive

to active stateful PCE as described in Section 5.8.2. When included

as part of the intended_attribute_list, the meaning of the BANDWIDTH

object is the requested bandwidth as intended by the operator. In

this case, the BANDWIDTH Object-Type of 1 SHOULD be used. Similarly,

to indicate a limiting constraint, the METRIC object SHOULD be

included as part of the intended_attribute_list with the B flag set

and with a specific metric value. To indicate the optimization

metric, the METRIC object SHOULD be included as part of the

intended_attribute_list with the B flag unset and the metric value

set to zero. Note that the intended_attribute_list is optional and

thus may be omitted. In this case, the PCE MAY use the values in the

actual_attribute_list as the requested parameters for the path.

The actual_attribute_list consists of the actual computed and

signaled values of the BANDWIDTH and METRIC objects defined in

[RFC5440]. When included as part of the actual_attribute_list,

Object-Type 2 ([RFC5440]) SHOULD be used for the BANDWIDTH object and

the C flag SHOULD be set in the METRIC object ([RFC5440]).
Best Regards,

Stephane

From: Fatai Zhang [mailto:zhangfa...@huawei.com]
Sent: Thursday, April 14, 2016 09:39
To: LITKOWSKI Stephane OBS/OINIS; DUGEON Olivier IMT/OLN; Aissaoui, Mustapha (Nokia - CA); adr...@olddog.co.uk; 'Dhruv Dhody'
Cc: pce@ietf.org
Subject: 答复: [Pce] Whither Stateless PCE?
Hi Stephane,

Could you clarify what is interoperability issue in multivendor environment (multivendor in one administrative domain?)?

Do you mean there is interoperability issue when vendor 1 supports stateless PCE and vendor 2 supports stateful PCE?

Thanks

Fatai

发件人: Pce [mailto:pce-boun...@ietf.org] 代表 stephane.litkow...@orange.com
发送时间: 2016年4月9日 1:04
收件人: DUGEON Olivier IMT/OLN; Aissaoui, Mustapha (Nokia - CA); adr...@olddog.co.uk; 'Dhruv Dhody'
抄送: pce@ietf.org
主题: Re: [Pce] Whither Stateless PCE?

Hi,

I fully agree that stateful PCE draft needs to be more clear about how a PCC retrieves a path when the delegation starts and the LSP has just been configured (does it need to compute locally first and then delegate, or do PCReq as Olivier proposed …).

I want to add my voice to what Olivier said about the inconsistent behaviors we see today in implementations leading to lack of interoperability.

The most important point is that we need to find a solution as soon as possible as some people wants to deploy it in multivendor environment and find workaround (btw vendor1 and vendor 2) to fix it interop is not the right way to go …

This is a question that the WG must work on and close asap.

Best Regards,

Stephane

From: Pce [mailto:pce-boun...@ietf.org] On Behalf Of olivier.dug...@orange.com
Sent: Friday, April 08, 2016 18:29
To: Aissaoui, Mustapha (Nokia - CA); adr...@olddog.co.uk; 'Dhruv Dhody'
Cc: pce@ietf.org
Subject: Re: [Pce] Whither Stateless PCE?

Hello all,

IMHO the discussion must be split into is 2 different subjects:

1/ PCInit message could be seen as an independent message compared to other PCReq/PCRep, PCRpt and PCUp. Indeed, the PCE uses the PCInit message after a request that comes from another interface (e.g. a RestConf API) instead of PCReq that comes from the router itself through PCEP. In fact, when you configure a tunnel on the router, only the path computation part is requested to the PCE. Complements of tunnel configuration still remain in the router configuration. In case of PCInit, all information must be provided to the router. This could be for example the traffic steering. So, IMHO, it is normal that the PCInit message evolves through extensions different from the other PCEP messages, and in particular PCReq, as it is not triggered by the same entity, i.e. an external component instead the PCC router itself.

2/ But, this will not make PCReq message obsolete. Indeed, RFC5440 will continue to be mandatory for stateful both passive and active mode even if it needs clarification in the draft. Let me explain. In passive stateful, a PCReq/PCRep sequence is drawn in Figure 7 of the pce stateful draft prior to the PCRpt message Now, the ambiguity comes from the active stateful mode and figure 8. Why is the PCReq/PCRep sequence not mentioned? Of course the tunnel is delegated in this mode, but, the delegation object has been added as an extension to the PCReq message in the same draft. So, IMHO, at the creation of the tunnel, the draft must precise that a PCReq/PCRep exchange with delegation=1 must be used prior to the PCRpt to be coherent with RFC 5440 and passive stateful mode.

The problem occured during our evaluation of commercial products on which we made interoperability tests. Indeed we observed different behaviours that are due to the draft ambiguity and conduct to some interoperability issues. The different cases are as follow:
- a/ - PCReq/PCRep exchange to obtain a valid ERO before the PCRpt message
- b/ - PCReq message to obtain a valid ERO but with no reaction from the PCE which is not conform to RFC5440
- c/ - PCRpt with empty ERO (looks strange. What is the meaning of an Empty ERO ? a loose path ? no path ? )/PCupd to get a valid path which overlaps with standard RFC5440 PCReq/PCRep.
- d/ - PCRpt with empty ERO and no PCUpd leaving the tunnel down.

Thus, PCC/PCE that used PCRpt/PCupd messages for active stateful mode are incompatible with PCC/PCE that used standard PCReq/PCrep exchange. We could not mix both behaviours (PCC that use PCReq message with PCE that react to PCRpt with empty ERO and reciprocally). The problem occurs only at the creation of the tunnel. Once created and up the tunnel is reported and updated by means of PCRpt / PCupd messages correctly in all cases.

To summarize: PCInit message could leave independently from other messages. PCReq is the basis of PCE and is mandatory in all use cases included the active stateful mode, but this need to be clarify in the pce stateful draft.

Regards

Olivier

Le 07/04/2016 23:22, Aissaoui, Mustapha (Nokia - CA) a écrit :
Hi Adrian,

I raised in December 2014 the technical issue in draft-ietf-pce-stateful-pce that a PCC must be able to convey the original parameters (constraints) of the LSP path (Bandwidth, Metric, and LSPA objects) using a PCReq message to a PCE and subsequently delegate the LSP to PCE using the PCRpt message. Otherwise, when the LSP is delegated to PCE only the operational values of these parameters can be included in the PCRpt message. The latter means that the PCE will update the path without knowing exactly the original parameters.

For me, PCReq/PCRep are an integral part of operating an LSP in stateful mode.

Here is the link to the archived thread:

https://mailarchive.ietf.org/arch/search/?email_list=pce&so=-date&q=%22+Path+Computation+Request+in+Active+Stateful+PCE%22

Regards,

Mustapha.

From: Pce [mailto:pce-boun...@ietf.org] On Behalf Of EXT Adrian Farrel
Sent: Thursday, April 07, 2016 12:48 AM
To: 'Dhruv Dhody'
Cc: pce@ietf.org
Subject: Re: [Pce] Whither Stateless PCE?

I think you are probably right, Dhruv.

But referencing the ways in which customers deploy may be a little limiting.

To say PCE is widely deployed (even after all these years) may be an exaggeration.

Although we do have some clues about what is currently being pushed for deployment.

I think you have mainly grasped my point, however. We need to understand which extensions are definitely only needed in one mode or another, and which should be done in all modes (either because they are needed or because we don't know).

OTOH, I suppose TLVs are just TLVs. Once you specified the TLV it is not rocket science to include it in a message. In fact, it is probably one line of text to include it and only a short paragraph to describe additional processing in other modes once you have described how it is used in one mode.

Where does that leave us?

Adrian

From: dhruvdh...@gmail.com [mailto:dhruvdh...@gmail.com] On Behalf Of Dhruv Dhody
Sent: 06 April 2016 23:07
To: Farrel Adrian
Cc: pce@ietf.org
Subject: Re: [Pce] Whither Stateless PCE?

Hi Adrian,

Even in the brave new world of Stateful PCE, PCReq and PCRep messages do play a role in the passive stateful PCE mode. PCReq/PCRep also play a crucial role in the inter-domain and inter-layer context in the new proposal like stateful H-PCE.

At the same time mandating that every extension (say SFC) must also be specified in a stateless manner when no customer deploy in such a way, might be overkill.

Perhaps we need to look at it case by case!

Dhruv

On Wed, Apr 6, 2016 at 4:00 PM, Adrian Farrel <adr...@olddog.co.uk> wrote:

Once upon a time, in a working group far, far away, PCE was basically stateless.
PCE acted in response to questions asked by PCCs.

These days, everyone is excited by stateful PCEs and there is a lot of
initiation (of LSPs or of control of LSPs).

In the jabber room during today's meeting Ravi noted that not a lot of the new
drafts (maybe none of them) talk about PCReq messages. This raises the question
in our minds as to whether stateless PCE is obsolete.

If (and only if) this mode of PCE usage has gone out of fashion, we *might*
consider cleaning up the protocol and architecture so that we don't need to make
protocol extensions to PCReq and PCRep messages when we make extensions to
PCInit messages.

Thoughts?

Adrian

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Re: [Pce] Whither Stateless PCE?

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