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

Mahesh Jethanandani <> Wed, 02 August 2017 00:51 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 17:52:01 -0700
Cc: Yingzhen Qu <>, "Acee Lindem (acee)" <>, "" <>, "" <>, "" <>, Reshad Rahman <>
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References: <> <> <> <> <> <> <> <> <> <> <>
To: Jeffrey Haas <>
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> On Aug 1, 2017, at 9:33 AM, Jeffrey Haas <> wrote:
> On Tue, Aug 01, 2017 at 08:33:38AM -0700, Mahesh Jethanandani wrote:
>>> 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. 
> The protocol does. But that doesn't mean the config model should.

Ok. I have removed the separate configuration values for tx/rx min intervals for echo model. Now, there is only one set of tx/rx values.

>>> This minimally suggests that there should be a "use echo mode" flag.
>> Will add a boolean to enable/disable echo mode.
> I think that's a good start.

This is what we have now in client-cfg-parms

    container echo-mode {
      if-feature echo-mode;
      leaf echo-mode-enabled {
        type boolean;
        default false;
          "Should be set to true if echo-mode is enabled for this
           session. Set to false by default because defining the
           feature should not enable echo-mode by default.";

Yingzhen, there is one other change that you should be aware of. There is no longer a choice between configuring tx/rx values and a single value for both. Even if the values are the same for tx and rx, you need to configure each of them explicitly. 

I will be uploading the changes shortly.


>>> 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.
> Right.  So, again need to check real world implementations.
> If it's the case that implementations supporting echo only use a single set
> of the intervals for echo or not, then we only need that in the model.  
> If it becomes the case that an implementation supports echo intervals
> differently, a vendor *could* augment the model to support such values.
> However, since this is imported via grouping, it means that the augmentation
> has to be done in each module that uses the grouping.
> I hate yang grouping augmentation rules. :-P
> -- Jeff

Mahesh Jethanandani