Re: [netmod] 6991bis: address-with-prefix-length

Martin Bjorklund <mbj@tail-f.com> Thu, 18 April 2019 12:18 UTC

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To: j.schoenwaelder@jacobs-university.de
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From: Martin Bjorklund <mbj@tail-f.com>
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Subject: Re: [netmod] 6991bis: address-with-prefix-length
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Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de> wrote:
> On Thu, Apr 18, 2019 at 10:41:11AM +0200, Ladislav Lhotka wrote:
> > > > 
> > > > I am not in favour of adding this type. Having ip-prefix next to
> > > > ip-address-and-prefix is confusing.
> > > 
> > > Confusing or not, they are NOT interchangeable and actually do different 
> > > things, which is why both are needed. There's plenty of precedence to
> > 
> > I actually agree with you. It is a historical accident that these
> > two different things got mixed up (and some vendors contributed to
> > this). I would argue that
> >
> > - IP prefix is a set of IP addresses, and as such can be thought of
> >   as a single entity.
> > 
> > - IP address and subnet mask/prefix are two separate things, the
> >   latter being an instruction for routing to *other* destination
> >   addresses.
> 
> I think we should be pragmatic. There are other common types that are
> in fact constructed out of simpler types, date-and-time is a prime
> example of a type constructed out of a date value and a time value.

I think that date-and-time represents one thing - a single point in
time.

> It
> is sometimes convenient to treat something that is in fact constructed
> as an atomic value.

Convenient for users that enter these values, perhaps.  But not as
convenient for a program (or a filter) that needs one of the combined
values.  For example, suppose I want to find all entries with a given
prefix; that is non-trivial with a combined ip-address-and-prefix
type.


/martin