Re: [netmod] Adam Roach's No Objection on draft-ietf-netmod-rfc6087bis-18: (with COMMENT)

Robert Wilton <> Fri, 09 March 2018 14:58 UTC

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To: Adam Roach <>, Andy Bierman <>
Cc: NetMod WG Chairs <>, NetMod WG <>, The IESG <>,
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From: Robert Wilton <>
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Date: Fri, 9 Mar 2018 14:58:31 +0000
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Subject: Re: [netmod] Adam Roach's No Objection on draft-ietf-netmod-rfc6087bis-18: (with COMMENT)
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Hi Adam,

On 08/03/2018 23:55, Adam Roach wrote:
> Thanks for your quick response! I have some additional comments inline.
> Clearly, the items that have already been published can't be changed, 
> but it seems like there is room for guidance about whether to optimize 
> for simple regexes, or for more rigorous ones.
I agree with your general sentiment.  In fact I had a long protracted 
discussion on this point on the Netmod WG alias.

Sometimes pattern statements can be both correct and also concise and 
readable.  This is the easy case.

But for other regular expressions (e.g. route-target in rfc8294) there 
is a clear choice whether to make the regex as precise as possible 
(minimizing false values), or to make it concise and hopefully 
readable/verifiable but allowing for more false values.

My personal preference is for a simpler, but less precise regex over a 
more precise, but hard to visually verify, regex.  E.g. I'm not a fan of 
using regular expressions to limit the range of numerical values.  I 
know that validating regular expression matches is computationally 
expensive, so I wonder if implementations will end up replacing these 
larger regular expressions with custom written verification code that is 
more performant.  But, as I recall, I was in the rough on this issue.

If the consensus is that they should be as accurate as is feasible then 
I think that it would be helpful if the guidelines state this as a 
goal.  This would seem to ensure consistency in the YANG models that are 
being standardized.


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