Re: [Pce] WG Last Call for draft-ietf-pce-binding-label-sid-07 (and Code Point Allocation)

olivier.dugeon@orange.com Fri, 02 April 2021 09:52 UTC

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To: Dhruv Dhody <dd@dhruvdhody.com>
CC: "draft-ietf-pce-binding-label-sid@ietf.org" <draft-ietf-pce-binding-label-sid@ietf.org>, "pce@ietf.org" <pce@ietf.org>
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Subject: Re: [Pce] WG Last Call for draft-ietf-pce-binding-label-sid-07 (and Code Point Allocation)
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Hi Dhruv,

After re-thinking about the new text, I discovered another potential mistake:

Example, you have 3 BSID: BSID1, BSID2, BSID3.

To remove BSID2, PCE should send a PcUpd message with only BSID1 and BSID3
Once remove, if PCE would modify BSID3, it should send a PcUpd message with BSID1 and new BSID3

So, how do you make the distinction, from a protocol and parsing point of view, between
a PcUpdate message that is used to i) remove a BSID from ii) update a BSID ?

In fact, if I correctly understand, the proposed mechanism impose to synchronise
permanently the whole list of BSID instead of managing individual BSID,
which, IMHO, is preferable.

Regards

Olivier

Le 01/04/2021 à 12:19, olivier.dugeon@orange.com a écrit :
> Hi Dhruv,
>
> New text is better, but the solution remains perfectible and not safer.
> Again, it makes the assumption that PCE and PCC are perfectly synchronised regarding
> the TE-PATH-BINDING table which could not be the case. This mechanism is only working
> well if implementation has been correctly written. In case of error, bug, whatever you could
>
> imagine, removal of TE-PATH-BINDING could not work as expected.
> From a protocol pointof view, it is not safer. In PCEP, there is a 'R' flag when you would
> remove an LSP with thePcUpdate/PcInitiate message. For me, it is the same behaviour.
> You explicitly remove an LSPby providing the LSP information + the 'R' flag set.
> I don't understand why it is not the samefor all PCEP TLVs.
>
> Regards
>
> Olivier
>
> Le 31/03/2021 à 20:38, Dhruv Dhody a écrit :
>> Hi Olivier, 
>>
>> On Wed, Mar 31, 2021 at 11:30 PM <olivier.dugeon@orange.com <mailto:olivier.dugeon@orange.com>> wrote:
>>
>>     Hi Cheng, Aijun,
>>
>>     I think that the 'R' bit to clearly indicate that BSID is removed
>>     is mandatory. In fact, in case of multiple BSID, it will become clearly
>>     a nightmare from an implementation point of view to manage the removal.
>>
>>     Let me take a simple example:
>>
>>     Assume a PCE would setup some BSID into a PCC. It first send a PcInitiate
>>     message with an empty TE-PATH-BINDING TLV to request a BSID. PCC send a PcRpt
>>     message with a BSID=1 (simple value). Then, the PCE would a second BSID. So, it
>>     sends a PcUpdate message with a TE-PATH-BINDING TLV and the first BSID=1 and a
>>     second empty TE-PATH-BINDING TLV to get the second one. PCC sends back a PcRpt
>>     message with the 2 TE-PATH-BINDING BSID=1 and BSDI=2. We repeat the last operation
>>     to collect a third BSID=3. Now the PCE would remove the BSID=2. It must send a
>>     PcUpdate message with TE-PATH-BINDING BSID=1, TE-PATH-BINDING BSID=3 and an
>>     empty TE-PATH-BINDING.
>>
>>     So, how the PCC could determine that this last emptyTE-PATH-BINDING corresponds
>>     to a deletion and not a creation ?
>>
>>
>> Looking at the working copy[1]/diff[2] that Cheng posted, the empty TE-PATH-BINDING TLV is used to request allocation only (and not to withdraw old values). So in the example above to remove BSID=2, the PCUpd message with TE-PATH-BINDING BSID=1 & TE-PATH-BINDING BSID=3 are sent.
>>
>> Adrian provided some cleaner text that has been incorporated for this now. Does the updated text resolve this?
>>
>> Thanks!
>> Dhruv (as a WG participant)
>>
>> [1] https://raw.githubusercontent.com/dhruvdhody/ietf/master/draft-ietf-pce-binding-label-sid-08.txt
>> [2] https://tools.ietf.org/rfcdiff?url1=https://www.ietf.org/archive/id/draft-ietf-pce-binding-label-sid-07.txt&url2=https://raw.githubusercontent.com/dhruvdhody/ietf/master/draft-ietf-pce-binding-label-sid-08.txt
>>  
>>
>>     There is a large risk of ambiguity in particular if the PCE does not send
>>     the TE-PATH-BINDING TLVs in the right order, if PCE and PCC become de-synchronize
>>     on the number of BSID ...
>>
>>     Thus, I think that a 'R' bit for deletion is mandatory.
>>
>>     Regards
>>
>>     Olivier
>>
>>     Le 26/03/2021 à 03:46, Chengli (Cheng Li) a écrit :
>>     > Hi Aijun,
>>     >
>>     > Many thanks for your comments! Please see my reply inline. The diff is attached.
>>     >
>>     > Respect,
>>     > Cheng
>>     >
>>     >
>>     >
>>     > -----Original Message-----
>>     > From: Aijun Wang [mailto:wangaijun@tsinghua.org.cn <mailto:wangaijun@tsinghua.org.cn>]
>>     > Sent: Monday, March 22, 2021 11:57 AM
>>     > To: julien.meuric@orange.com <mailto:julien.meuric@orange.com>; pce@ietf.org <mailto:pce@ietf.org>
>>     > Cc: draft-ietf-pce-binding-label-sid@ietf.org <mailto:draft-ietf-pce-binding-label-sid@ietf.org>
>>     > Subject: RE: [Pce] WG Last Call for draft-ietf-pce-binding-label-sid-07 (and Code Point Allocation)
>>     >
>>     > Hi,
>>     >
>>     > 1. The concept of PCC requests the allocating of BSID for a LSP is clear, but the scenario that PCE allocate the BSID is not convincible.
>>     >   PCE can request the PCC to allocate the BSID for one LSP. It should not allocate the value directly.
>>     >
>>     >
>>     > [Cheng]Section 8 is optionally used when PCE is in control of label space (PCECC) and would not be used for vanilla stateful PCE.
>>     >
>>     > 2. What's the reason to include the BT=3, that is "SRv6 Endpoint Behavior and SID Structure"? It is one general information and not close connection to the normal usage of BSID.
>>     > [Cheng] This is an alignment with other SIDs. In order to support backward compatibility, we want to remain BT2, and introduce a new BT for support SID structure. It can be used for future use case.
>>     >
>>     >
>>     > 3. Will it be more clear to define one new bit(R bit) within the Flag field of "TE-PATH-BINDING TLV" to indicate clearly the remove of BSID allocation to a LSP? Instead of the implicit method that depending on the presence of TE-PATH-BINDING TLV as described in current draft?
>>     > [Cheng] It is possible. But there are existing implementations that would get impacted.
>>     >
>>     >
>>     > 4. For BT=0, the length is set to 7. How to skip the padding trailing zeros to a 4-octet boundary when parsing?
>>     > [Cheng] We have updated the description of BT=0 as per Adrian's comment. Length=7 and handling of padding is as per RFC5440:
>>     >
>>     >    The Length field defines the length of the value portion in bytes.
>>     >    The TLV is padded to 4-bytes alignment; padding is not included in
>>     >    the Length field (so a 3-byte value would have a length of 3, but the
>>     >    total size of the TLV would be 8 bytes).
>>     >
>>     > Best Regards
>>     >
>>     > Aijun Wang
>>     > China Telecom
>>     >
>>     > -----Original Message-----
>>     > From: pce-bounces@ietf.org <mailto:pce-bounces@ietf.org> <pce-bounces@ietf.org <mailto:pce-bounces@ietf.org>> On Behalf Of julien.meuric@orange.com <mailto:julien.meuric@orange.com>
>>     > Sent: Thursday, March 18, 2021 7:09 PM
>>     > To: pce@ietf.org <mailto:pce@ietf.org>
>>     > Cc: draft-ietf-pce-binding-label-sid@ietf.org <mailto:draft-ietf-pce-binding-label-sid@ietf.org>
>>     > Subject: [Pce] WG Last Call for draft-ietf-pce-binding-label-sid-07 (and Code Point Allocation)
>>     >
>>     > Hi all,
>>     >
>>     > This message initiates a 2-week PCE WG Last Call for draft-ietf-pce-binding-label-sid-07. Please review and share your feedback, whatever it is, using the PCE mailing list. This WGLC will end on Thursday April 1st (no kidding).
>>     >
>>     >
>>     > Moreover, we have received a request from the authors for a code point allocation to support interoperability testing.
>>     >
>>     > RFC 7120 requires to meet the following criteria to proceed:
>>     >
>>     > b. The format, semantics, processing, and other rules related to handling the protocol entities defined by the code points (henceforth called
>>     > "specifications") must be adequately described in an Internet-Draft.
>>     > c. The specifications of these code points must be stable; i.e., if there is a change, implementations based on the earlier and later specifications must be seamlessly interoperable.
>>     >
>>     > If anyone believes that the draft does not meet these criteria, or believes that early allocation is not appropriate for any other reason, please send an email to the PCE mailing list explaining why. If the chairs hear no objections by Thursday, March 25th, we will kick off the "early" allocation request.
>>     >
>>     > Thanks,
>>     >
>>     > Dhruv & Julien
>>     >
>>     >
>>     > ____________________________________________________________________________
>>     > _____________________________________________
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>>      
>>
>>     Olivier Dugeon
>>     Orange Expert, Future Networks
>>     Open Source Referent
>>     Orange/IMT/OLN/WTC/IEE/iTeQ
>>
>>      
>>
>>     fixe : +33 2 96 07 28 80
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>>     olivier.dugeon@orange.com <mailto:olivier.dugeon@orange.com> <mailto:olivier.dugeon@orange.com <mailto:olivier.dugeon@orange.com>>
>>
>>
>>     _________________________________________________________________________________________________________________________
>>
>>     Ce message et ses pieces jointes peuvent contenir des informations confidentielles ou privilegiees et ne doivent donc
>>     pas etre diffuses, exploites ou copies sans autorisation. Si vous avez recu ce message par erreur, veuillez le signaler
>>     a l'expediteur et le detruire ainsi que les pieces jointes. Les messages electroniques etant susceptibles d'alteration,
>>     Orange decline toute responsabilite si ce message a ete altere, deforme ou falsifie. Merci.
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>
>  
>
> Olivier Dugeon
> Orange Expert, Future Networks
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> Orange/IMT/OLN/WTC/IEE/iTeQ
>
>  
>
> fixe : +33 2 96 07 28 80
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> olivier.dugeon@orange.com <mailto:olivier.dugeon@orange.com>
> _________________________________________________________________________________________________________________________
>
> Ce message et ses pieces jointes peuvent contenir des informations confidentielles ou privilegiees et ne doivent donc
> pas etre diffuses, exploites ou copies sans autorisation. Si vous avez recu ce message par erreur, veuillez le signaler
> a l'expediteur et le detruire ainsi que les pieces jointes. Les messages electroniques etant susceptibles d'alteration,
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>
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Open Source Referent
Orange/IMT/OLN/WTC/IEE/iTeQ

 

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_________________________________________________________________________________________________________________________

Ce message et ses pieces jointes peuvent contenir des informations confidentielles ou privilegiees et ne doivent donc
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Orange decline toute responsabilite si ce message a ete altere, deforme ou falsifie. Merci.

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