RE: [Pce] Review of draft-ietf-pce-stateful-pce-18

[Jonathan Hardwick <[e-mail]>]

Hi Julien

You are right, but it is *really easy* for the reader to confuse "stateful capability" with "update capability" and "active stateful capability".  Case in point: I just confused them in my reply to Lionel.

We should fix each of the three points below to make this clearer.

Cheers
Jon

-----Original Message-----
From: Julien Meuric [mailto:[e-mail]] 
Sent: 11 April 2017 16:00
To: Jonathan Hardwick <[e-mail]>; Lionel Morand <[e-mail]>; [e-mail]
Cc: [e-mail]; [e-mail]; [e-mail]
Subject: Re: [Pce] Review of draft-ietf-pce-stateful-pce-18

Jon, Lionel,

I believe Lionel got confused by the wording introduced in RFC 8051:
- no report, no update means stateless PCE;
- report, no update means passive stateful PCE;
- report and update means active (stateful) PCE.

More details below, [JM].

Thanks for the work,

Julien


Apr. 11, 2017 - [e-mail]:
> =====
> 
> [LM] active/passive mode are not  advertized in PCEP. s/if active 
> stateful PCE capability was not advertised/if stateful PCE capability 
> was not advertised
> 
> Jon> ACK
> 
> =====
[JM] NACK! ;-)
Actually, the passive mode is advertised using the Stateful-capability-object TLV with the U bit unset, the active mode by setting the U bit.

> =====
> 
> Note that even if the update capability has not been advertised, a PCE 
> can still accept LSP Status Reports from a PCC and build and maintain 
> an up to date view of the state of the PCC's LSPs.
> 
> [LM] I don't undersand. Is it not in contradiction with
> 
> "If the PCEP Speaker on the PCE supports the extensions of this draft 
> but did not advertise this capability, then upon receipt of a PCRpt 
> message from the PCC, it MUST generate a PCErr with error- type
> 19 (Invalid Operation), error-value 5 (Attempted LSP State Report if  
> active stateful PCE capability was not advertised) (see Section
> 8.5) and it SHOULD terminate the PCEP session."
> 
> Or does it mean that there is another way than PCRpt message for the  
> PCC to send LSP status reports to the PCE?
> 
> Jon> ACK.  I think that the statement in the draft is bogus and I
> propose to delete this sentence from it.
> 
> =====
[JM] I do not think that the text is bogus:
- case 1: no advertised capability on update but advertised on report (i.e. passive stateful) => no error message;
- case 2: no advertised capability on update nor report (i.e. stateless) => error.

> =====
> 
> [LM] Would it be useful to discover (using another TLV) whether the 
> PCE is an active/passive stateful PCE, as in IGP-based capabilities 
> discovery mechanism?
> 
> Jon> This can be inferred immediately from the U flag in the
> STATEFUL-PCE-CAPABILITY TLV.  Passive mode is synonymous with not 
> sending / handling PCUpd messages.
> 
> =====
[JM] The mechanism is there, but section 7.1.1 may deserve an explicit use of the "passive/active" terms, to make sure the capability terminology is aligned with the vocabulary in the IGP section.