Re: [spring] Draft for Node protection of intermediate nodes in SR Paths

Shraddha, Robert and all,
Regarding Robert's question:
I wonder if multi-hop IP BFD session with addresses used as /32 (or /128) prefixes serving as Nose SIDs of R8 and R7 respectively could be used as such a trigger by R7? Such a session would not respond to link failures, and I find it problematic to imagine a scenario when it would be kept UP in the case of a real node failure.

Of course such a session would have to be slow enough not to react to link failures. But it still couks be much faster than IGP conversion IMHO.

My 2c,
Sasha

Such

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________________________________
From: spring <spring-bounces@ietf.org> on behalf of Robert Raszuk <robert@raszuk.net>
Sent: Friday, November 22, 2019, 11:22
To: Shraddha Hegde
Cc: spring@ietf.org; rtgwg@ietf.org
Subject: Re: [spring] Draft for Node protection of intermediate nodes in SR Paths

Hi Shraddha,

I have one question to the document.

As you know the critical element for the effective protection of any scheme is the failure detection. On that your draft seems to have just one little paragraph:

   Note that R7 activates the node-protecting backup path when it
   detects that the link to R8 has failed.  R7 does not know that node
   R8 has actually failed.  However, the node-protecting backup path is
   computed assuming that the failure of the link to R8 implies that R8
   has failed.

Well IMO this is not enough. Specifically there can be a lot of types of node failure when link is still up. Moreover there can be even running BFD across the link just fine when say fabric failure occurs at R8.

While this is not solely issue with this draft, it is our common IETF failure to provide correct means of detecting end to end path or fragments of path failures (I am specifically not calling them segment here :).

For example I propose that to effectively detect R8 failure as node failure which is the topic of your proposal a mechanism is clearly defined and includes bi-dir data plane probes send between R7-R9, R3-R7, R4-R7, R4-R9, R3-R9

Many thx,
Robert.

On Fri, Nov 22, 2019 at 4:38 AM Shraddha Hegde <shraddha=40juniper.net@dmarc.ietf..org<mailto:40juniper.net@dmarc.ietf.org>> wrote:
WG,

This is the draft I pointed out that talks about solutions for providing node-protection.
It covers Anycast case as well as keeping forwarding plane longer.
https://tools.ietf.org/html/draft-hegde-spring-node-protection-for-sr-te-paths-05<https://clicktime.symantec.com/375SW6TBGPi2mN7V9YeVWGg6H2?u=https%3A%2F%2Ftools.ietf.org%2Fhtml%2Fdraft-hegde-spring-node-protection-for-sr-te-paths-05>

Review and comments solicited.

Rgds
Shraddha

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