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

Dhruv Dhody <dd@dhruvdhody.com> Fri, 02 April 2021 14:59 UTC

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From: Dhruv Dhody <dd@dhruvdhody.com>
Date: Fri, 2 Apr 2021 20:29:05 +0530
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To: olivier.dugeon@orange.com
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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 Olivier,

As a WG member...
On Fri, Apr 2, 2021 at 3:22 PM <olivier.dugeon@orange.com> wrote:

> 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
> ?
>
>
The key is for PCE to send all TE-PATH-BINDING TLVs that it wishes to apply
from that point on.

PCC compares them to the existing binding values to find -
- the binding values that are the same (no change, nothing needs to be done)
- the binding values that are missing from PCE (that needs to be deleted)
- the binding values that are new (that needs to be allocated)

There is no need to differentiate between (i) and (ii) in your example, the
processing at the PCC would be the same anyways.



> 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.
>
>
That is correct. PCEP speakers include all the TE-PATH-BINDING TLVs.

The author's preference for the current text seems to be to avoid impacting
existing implementations. It would be good to hear from implementors on
this!
Thanks!
Dhruv






> 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 point of view, it is not safer. In PCEP, there is a 'R'
> flag when you would
> remove an LSP with the PcUpdate/PcInitiate message. For me, it is the
> same behaviour.
> You explicitly remove an LSP by providing the LSP information + the 'R'
> flag set.
> I don't understand why it is not the same for 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> 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]
>> > Sent: Monday, March 22, 2021 11:57 AM
>> > To: julien.meuric@orange.com; pce@ietf.org
>> > Cc: 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 <pce-bounces@ietf.org> On Behalf Of
>> julien.meuric@orange.com
>> > Sent: Thursday, March 18, 2021 7:09 PM
>> > To: pce@ietf.org
>> > Cc: 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
> mobile : +33 6 82 90 37 85
> 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.
>
> This message and its attachments may contain confidential or privileged information that may be protected by law;
> they should not be distributed, used or copied without authorisation.
> If you have received this email in error, please notify the sender and delete this message and its attachments.
> As emails may be altered, Orange is not liable for messages that have been modified, changed or falsified.
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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
> mobile : +33 6 82 90 37 85
> 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.
>
> This message and its attachments may contain confidential or privileged information that may be protected by law;
> they should not be distributed, used or copied without authorisation.
> If you have received this email in error, please notify the sender and delete this message and its attachments.
> As emails may be altered, Orange is not liable for messages that have been modified, changed or falsified.
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