Re: I-D Action: draft-ietf-bfd-yang-06.txt

Mahesh Jethanandani <> Tue, 01 August 2017 15:33 UTC

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Subject: Re: I-D Action: draft-ietf-bfd-yang-06.txt
From: Mahesh Jethanandani <>
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Date: Tue, 1 Aug 2017 08:33:38 -0700
Cc: Yingzhen Qu <>, "Acee Lindem (acee)" <>, "" <>, "" <>, "" <>, Reshad Rahman <>
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To: Jeffrey Haas <>
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> On Aug 1, 2017, at 7:41 AM, Jeffrey Haas <> wrote:
> Mahesh,
> On Mon, Jul 31, 2017 at 05:17:34PM -0700, Mahesh Jethanandani wrote:
>>> My point, unless my very quick glance at the module mislead me, is that you can't configure to use echo mode - if it's supported - in the grouping imported by the IGPs.
>> In the current model, it is modeled as a separate grouping with its own set of parameters. The expectation is that implementations that want to define echo mode would use the grouping. Defining the parameters also implicitly defines that echo-mode is enabled. Are you saying that using the echo grouping is not enough? 
> Minimally, I'm saying the IGP use is not pulling in the echo grouping either
> directly or indirectly.

Ahh! That is correct. I was not sure if you were pointing out an issue with the BFD model or the client model(s).

>> But I do think that the parameters needs to be further protected by an if-feature statement that says
>>  grouping echo-cfg-parms {
>>    if-feature echo-mode;
>>    description 
>>      "BFD grouping for echo config parameters”;
> This seems correct.
>>> My implementation doesn't support echo, so I don't have any opinion about where configuration of those belongs or not.
>> With the feature statement, these echo parameters can exist inside of client-cfg-parms, instead as a separate grouping and will be included by the platform only if the feature is defined. And this would be my preference. Is that what folks would also prefer?
> I'm ambivalent.  This depends really on real world behavior.
> As we saw from some brief googling yesterday on Cisco IOS/IOS-XR docs, that
> implementation doesn't appear to expose echo intervals as a separably
> configurable item.  It did, however, expose a boolean to disable echo.

True. But the standard seems to imply the ability to configure echo values separately. Worst case implementations would have to set both the values to be the same. 

> This minimally suggests that there should be a "use echo mode" flag.

Will add a boolean to enable/disable echo mode.

> The remaining homework is to figure out whether we should expose
> configuration state for echo directly in this version of the yang.

Per NMDA guidelines, unless the configuration state values are different from config, we do not need to model them as separate attributes.

> -- Jeff

Mahesh Jethanandani