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RE: Couple comments on draft-ali-spring-bfd-sr-policy

"Ketan Talaulikar (ketant)" <ketant@cisco.com> Tue, 20 March 2018 16:42 UTC

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From: "Ketan Talaulikar (ketant)" <ketant@cisco.com>
To: Greg Mirsky <gregimirsky@gmail.com>, "draft-ali-spring-bfd-sr-policy@ietf.org" <draft-ali-spring-bfd-sr-policy@ietf.org>, spring <spring@ietf.org>, "rtg-bfd@ietf.org" <rtg-bfd@ietf.org>
Subject: RE: Couple comments on draft-ali-spring-bfd-sr-policy
Thread-Topic: Couple comments on draft-ali-spring-bfd-sr-policy
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Date: Tue, 20 Mar 2018 16:42:40 +0000
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Hi Greg,

Thanks for your review and comments. Please check inline below for responses.


From: Greg Mirsky <gregimirsky@gmail.com>
Sent: 20 March 2018 08:57
To: draft-ali-spring-bfd-sr-policy@ietf.org; spring <spring@ietf.org>; rtg-bfd@ietf.org
Subject: Couple comments on draft-ali-spring-bfd-sr-policy

Dear Authors,
I've read the new draft and would appreciate your consideration of my comments and questions:

  *   if I understand correctly, you prefer using S-BFD in SR domain over use of the base BFD. Without arguing with your choice, I'll note that the title of the draft doesn't reflect your preference;
[KT] The choice of title seemed correct since the draft does analysis of the different BFD options for SR Policies before preferring SBFD.

  *   section 3.4 RFC 7882 already describes use of S-BFD in SR domain. What you is missing in the RFC 7882?
[KT] RFC7882 describes the SBFD use cases and its applicability to SR. This draft does comparison between the BFD modes that borrows from RSVP-TE tunnels usage against S-BFD mode to analyze what is more suitable for SR Policies. This analysis is important to document and to indicate why the authors propose S-BFD rather than BFD is more suitable for SR Policies.

  *   on more technical side. Use of S-BFD will still result in multiplicity of S-BFD packets reflected by egress to ingress. To avoid that we propose method to use BFD Demand mode in MPLS data plane as described in draft-mirsky-bfd-mlps-demand<https://tools.ietf.org/html/draft-mirsky-bfd-mpls-demand-02>. It will be presented in BFD WG meeting and discussed in SPRING as part of BFD in SPRING presentation.
[KT] The BFD on-demand proposal along with the draft-mirsky-spring-bfd basically re-uses concepts like need for bootstrap with LSP ping, setup of state on the egress router from RSVP-TE and IMHO is not suitable for SR Policies unlike S-BFD which is a much simpler and scalable solution that does not setup a per SR Policy state on the egress node.
Thanks,
Ketan
Regards,
Greg

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