Re: [Pce] Benjamin Kaduk's Discuss on draft-ietf-pce-stateful-hpce-13: (with DISCUSS and COMMENT)
Benjamin Kaduk <kaduk@mit.edu> Sun, 13 October 2019 21:46 UTC
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Date: Sun, 13 Oct 2019 14:46:09 -0700
From: Benjamin Kaduk <kaduk@mit.edu>
To: Dhruv Dhody <dhruv.ietf@gmail.com>
Cc: The IESG <iesg@ietf.org>, draft-ietf-pce-stateful-hpce@ietf.org, Adrian Farrel <adrian@olddog.co.uk>, pce-chairs <pce-chairs@ietf.org>, pce@ietf.org
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Subject: Re: [Pce] Benjamin Kaduk's Discuss on draft-ietf-pce-stateful-hpce-13: (with DISCUSS and COMMENT)
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On Thu, Sep 26, 2019 at 12:11:56PM +0530, Dhruv Dhody wrote: > Hi Ben, > > Snipping to the final discuss that is still open - > > > > > > ---------------------------------------------------------------------- > > > > DISCUSS: > > > > ---------------------------------------------------------------------- > > > > > > > > I think this should be pretty easy to resolve, though I'm not sure what > > > > the right way to do so it. > > > > > > > > Section 3 says: > > > > > > > > [I-D.ietf-pce-hierarchy-extensions] defines the H-PCE Capability TLV > > > > that is used in the Open message to advertise the H-PCE capability. > > > > [RFC8231] defines the Stateful PCE Capability TLV used in the Open > > > > message to indicate stateful support. The presence of both TLVs in > > > > an Open message indicates the support for stateful H-PCE operations > > > > as described in this document. > > > > > > > > There is no normative reference relationship (in either direction) > > > > between draft-ietf-pce-hierarchy-extension and this document; I think > > > > that the use of the capability TLV to imply both sets of functionality > > > > implies some sort of normative relationship; we wouldn't want version > > > > skew between documents to induce breaking changes. In particular, an > > > > implementation that already supports RFC 8231 and is implementing the > > > > hierarchy extensions would need to know to look at this document *and > > > > implement it*, or would unknowingly be noncompliant with this document > > > > and fail to interoperate with a peer that is compliant with this > > > > document. > > > > > > > > > > How about we add normative text for this - > > > > > > [I-D.ietf-pce-hierarchy-extensions] defines the H-PCE Capability TLV > > > that is used in the Open message to advertise the H-PCE capability. > > > [RFC8231] defines the Stateful PCE Capability TLV used in the Open > > > message to indicate stateful support. To indicates the support for > > > stateful H-PCE operations described in this document, a PCEP speaker > > > MUST include both TLVs in an Open message. It is RECOMMENDED that any > > > implementation that supports stateful operations [RFC8231] and H-PCE > > > [I-D.ietf-pce-hierarchy-extensions] would also implements the > > > stateful H-PCE operations as described in this document. > > > > > > This would be true in most deployments/implementations of C-PCE and > > > P-PCE that are also stateful! > > > > This does remove the problematic normative requirement on implementations > > of other documents, but I'm not sure if it does what's needed for the > > interactions across documents. Specifically, what will happen if two peers > > both support/advertise stateful PCE and H-PCE but only one implements > > stateful HPCE? Will there be a clean error handling at runtime and > > degredation to one or the other, or will there be messy errors? If the > > latter, then I don't think we can just have a RECOMMENDED relationship. > > > > The assumption was that any implementation that claims to support > stateful and H-PCE on a particular session would also support Stateful > H-PCE and this document just describes the interaction between these > two features as an informational document. > > But, lets take a case where PCC and P-PCE support stateful H-PCE but > the C-PCE does not. PCC would send stateful message to C-PCE and C-PCE > would not further propagate them. > > I further did a mental exercise for PCC -> C-PCE -> P-PCE and assumed > all support stateful and H-PCE extension but what happens when any > PCEP speaker does not support stateful H-PCE but the peer assumes that > it does. On further PCEP message exchange, the messages may not get > further propagated and thus at worse would not lead to the stateful > H-PCE based 'parent' control of the LSP. This is something any peer > should be prepared for anyways. > > The "clean" solution would be to add a new flag; but then we also need > to move this a standards track and loose the claim that this is just a > combination of existing protocol extensions. Thanks for going through the mental exercise; I will trust your judgment that a new flag is not really needed in practice. Sorry for the slow response... -Ben
- [Pce] Benjamin Kaduk's Discuss on draft-ietf-pce-… Benjamin Kaduk via Datatracker
- Re: [Pce] Benjamin Kaduk's Discuss on draft-ietf-… Dhruv Dhody
- Re: [Pce] Benjamin Kaduk's Discuss on draft-ietf-… Benjamin Kaduk
- Re: [Pce] Benjamin Kaduk's Discuss on draft-ietf-… Dhruv Dhody
- Re: [Pce] Benjamin Kaduk's Discuss on draft-ietf-… Benjamin Kaduk