Re: [Idr] Some comments about the flags in draft-ietf-idr-te-lsp-distribution-11

"Ketan Talaulikar (ketant)" <ketant@cisco.com> Wed, 03 July 2019 14:13 UTC

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From: "Ketan Talaulikar (ketant)" <ketant@cisco.com>
To: "Dongjie (Jimmy)" <jie.dong@huawei.com>, "draft-ietf-idr-te-lsp-distribution@ietf.org" <draft-ietf-idr-te-lsp-distribution@ietf.org>
CC: "idr@ietf.org" <idr@ietf.org>
Thread-Topic: Some comments about the flags in draft-ietf-idr-te-lsp-distribution-11
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Date: Wed, 03 Jul 2019 14:13:14 +0000
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Subject: Re: [Idr] Some comments about the flags in draft-ietf-idr-te-lsp-distribution-11
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+ IDR list

Hi Jie,

Please check inline below for responses.

From: Dongjie (Jimmy) <jie.dong@huawei.com>
Sent: 03 June 2019 08:26
To: draft-ietf-idr-te-lsp-distribution@ietf.org
Subject: Some comments about the flags in draft-ietf-idr-te-lsp-distribution-11

Dear coauthors,

After reviewing the latest version of this draft, here are some comments about the description of the flags:


1)      6.1. SR Binding SID
*  S-Flag : Indicates the BSID value in use is specified or provisioned value when set and dynamically allocated value when clear.

o  Provisioned BSID: Optional field used to report the explicitly provisioned BSID value as indicated by the S-Flag being clear.
When the provisioned BSID is unavailable, there can be two cases, in the first case a dynamically allocated BSID is used, in another case a statically configured BSID is used.
[KT] Provisioned BSID indicates a statically configured (when using a mgmt. interface like CLI or Yang) or signaled (when using a protocol like PCEP or BGP-SRTE) value. The Provisioned BSID field never carries a dynamically allocated value. So we only have the second case you mention.

In both cases the Provisioned BSID needs to be reported using BGP-LS, which means the provisioned BSID needs to be reported regardless of the value of the S-flag. Thus it is suggested to remove “as indicated by the S-Flag being clear.”
[KT] The S-flag indicates whether the CP had a provisioned BSID value or not. I think it would be clearer if the text was “Optional field used to report the explicitly provisioned BSID value when the S-Flag is set.” We can fix this in the next version if you agree.



2)      6.2. SR Candidate Path State
      *  V-Flag : Indicates the CP has at least one valid SID-List when set.

In some cases a candidate path may not be verified, should the V-flag also be set?  The similar cases are described in the V-flag definition in 6.5 “SR Segment List” and 6.6 “SR Segment”, where the V-flag is set when the verification was not required.
[KT] You are right that a CP may not be verified. We have an E flag that indicates whether it has been verified or not in the first place. So the V flag comes into picture only if E is set. Otherwise, validation has not been done and hence V flag is not set.

Thus it is suggested to use the similar statement in the definition of V-flag of SR Candidate Path State: “Indicates the CP has at least one valid SID-List or its verification was not required when set and failed verification when clear.”
[KT] Does it help to indicate explicitly that the V flag should be clear when the CP has not been verified (i.e. when E flag is clear)?

These are minor changes to the description of Flags, while they can help to clarify the setting of the flags in different cases.
[KT] Agree. Please let know your views and we can accordingly update the text in the next update.

Thanks,
Ketan

Thoughts?

Best regards,
Jie