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

Martin Bjorklund <mbj@tail-f.com> Tue, 02 April 2019 18:27 UTC

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Date: Tue, 02 Apr 2019 20:27:32 +0200 (CEST)
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To: rwilton@cisco.com
Cc: acee@cisco.com, j.schoenwaelder@jacobs-university.de, kristian@spritelink.net, netmod@ietf.org
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Subject: Re: [netmod] 6991bis: address-with-prefix-length
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"Rob Wilton (rwilton)" <rwilton@cisco.com>; wrote:
> Hi Acee,
> 
> Having re-read the thread, I think that "ip-address-prefix" is going
> to be confusing, since I had incorrectly assumed that the type being
> defined was an IP prefix, but as you have pointed out there is already
> a type for that.
> 
> I think that we need to choose this name very carefully or otherwise I
> suspect that folks will accidentally use the wrong type.
> 
> So having the type as "ip-address-and-prefix-length" or
> "ip-addr-and-prefix-len" now seems like a clearer choice to me.

The combined type really specifies (i) an ip address and (ii) an ip
prefix.  The prefix happens to be specified with a length indicator.
So I think the name "ip-address-and-prefix" is the correct one.

> I
> think that I also now agree with Martin that this is really merging
> two values into one leaf.

And for the record (again, perhaps), I think this is a bad idea in
general, and I am not sure an exception is needed in this case.


/martin


> Where is this type going to be used?  Is it only used for configuring
> host address/prefix?  Or are there other uses cases as well?
> 
> Thanks,
> Rob
> 
> 
> > -----Original Message-----
> > From: Acee Lindem (acee) <acee@cisco.com>;
> > Sent: 02 April 2019 16:52
> > To: Rob Wilton (rwilton) <rwilton@cisco.com>;; Martin Bjorklund
> > <mbj@tail-
> > f.com>; j.schoenwaelder@jacobs-university.de
> > Cc: netmod@ietf.org
> > Subject: Re: [netmod] 6991bis: address-with-prefix-length
> > 
> > Hi Rob,
> > 
> > ´╗┐On 4/2/19, 11:37 AM, "netmod on behalf of Rob Wilton (rwilton)"
> > <netmod-
> > bounces@ietf.org on behalf of rwilton@cisco.com>; wrote:
> > 
> > 
> > 
> >     > -----Original Message-----
> >     > From: netmod <netmod-bounces@ietf.org>; On Behalf Of Martin
> > Bjorklund
> >     > Sent: 02 April 2019 13:47
> >     > To: j.schoenwaelder@jacobs-university.de
> >     > Cc: netmod@ietf.org
> >     > Subject: Re: [netmod] 6991bis: address-with-prefix-length
> >     >
> >     > Juergen Schoenwaelder <j.schoenwaelder@jacobs-university.de>; wrote:
> >     > > If you go back ~20 messages, my proposal was ip-address-prefix,
> >     > > ipv4-address-prefix, and ipv6-address-prefix.
> >     >
> >     > Do we agree that this type really specifies two values in one?  If so
> >     > I think
> > the
> >     > "and" is useful.
> > 
> >     Isn't an "IP prefix" made up of an "IP address" and a "prefix length"?
> > 
> > This was my confusion as well since the ipv4-prefix and ipv6-prefix
> > types
> > (ietf-inet-types) have been used when they probably shouldn't have
> > been.
> > Note that they both have the constraint of not allowing the host bits
> > to be set
> > should they should be used in situations like interface address
> > assignment.
> > 
> > Excerpted from RFC6991 ipv4-type definition (note the last sentence):
> >      description
> >         "The ipv4-prefix type represents an IPv4 address prefix.
> >          The prefix length is given by the number following the
> >          slash character and must be less than or equal to 32.
> > 
> >          A prefix length value of n corresponds to an IP address
> >          mask that has n contiguous 1-bits from the most
> >          significant bit (MSB) and all other bits set to 0.
> > 
> >          The canonical format of an IPv4 prefix has all bits of
> >          the IPv4 address set to zero that are not part of the
> >          IPv4 prefix.";
> > 
> >     So, I think that the names above are probably right, or otherwise if
> >     you
> > want the "and" then perhaps it should be
> > "ip-address-and-prefix-length" -
> > which seems clunky?
> > 
> > I think the original suggestion of ipxx-address-prefix would be ok.
> > 
> > Thanks,
> > Acee
> > 
> >     Thanks,
> >     Rob
> > 
> > 
> >     >
> >     > Also note that the current text in RFC 6991 says:
> >     >
> >     >      The ipv4-prefix type represents an IPv4 address prefix.
> >     >
> >     > so having a type ipv4-address-prefix for something that is not (only)
> >     > an
> >     > "ipv4 address prefix" is imo confusing.
> >     >
> >     >
> >     > /martin
> >     >
> >     >
> >     >
> >     >
> >     > >
> >     > > /js
> >     > >
> >     > > On Tue, Apr 02, 2019 at 11:13:09AM +0000, tom petch wrote:
> >     > > > ----- Original Message -----
> >     > > > From: "Jeff Tantsura" <jefftant.ietf@gmail.com>;
> >     > > > To: <netmod@ietf.org>;; "Kristian Larsson" <kristian@spritelink.net>;
> >     > > > Sent: Monday, April 01, 2019 11:09 PM
> >     > > >
> >     > > > What Kristian has proposed makes sense, in favor.
> >     > > >
> >     > > > <tp>
> >     > > >
> >     > > > Yes, I support this idea and we should be able to come up with a
> >     > > > more user-friendly name;  address-prefix or address-length ?
> >     > > >
> >     > > > Tom Petch
> >     > > >
> >     > > > p.s.
> >     > > >
> >     > > >    identifier          = (ALPHA / "_")
> >     > > >                          *(ALPHA / DIGIT / "_" / "-" / ".")
> >     > > >
> >     > > > Cheers,
> >     > > > Jeff
> >     > > > On Apr 1, 2019, 1:09 PM -0700, Kristian Larsson
> >     > > > <kristian@spritelink.net>;, wrote:
> >     > > > > Hello Mahesh,
> >     > > > >
> >     > > > > On 2019-04-01 21:40, Mahesh Jethanandani wrote:
> >     > > > > >
> >     > > > > > > On Apr 1, 2019, at 10:29 AM, Martin Bjorklund <mbj@tail-
> > f.com>
> >     > > > wrote:
> >     > > > > > >
> >     > > > > > > I know that this type is convenient, esp. if you use it for
> >     > > > > > > manual input, but I wonder if it really is good practice to
> >     > > > > > > squeeze two values into one.
> >     > > > > >
> >     > > > > > Agree. The combination makes sense for CLI, but for modeling
> >     > > > > > the
> >     > > > address and prefix should be separate.
> >     > > > >
> >     > > > > Okay, then why do we have an ip-prefix data type at all? With the
> >     > > > > same line of argument you apply, it should be split up.
> >     > > > >
> >     > > > > So you're the third person bringing up CLI. I don't get this at
> >     > > > > all. I don't see how CLI are different from everything else. This
> >     > > > > is about
> >     > > > data
> >     > > > > modeling and data modeling is about expressing the world in a
> >     > > > > data
> >     > > > > modeling language. It's like painting a picture but instead of a
> >     > > > > brush you have a schema language like YANG. What do you see?
> >     > > > > Express it. It doesn't matter if the purpose is a CLI, a web page
> >     > > > > or just exposing it via NETCONF for another system to consume.
> >     > > > >
> >     > > > > I think address-and-prefix-length is natural. JUNOS uses this
> >     > > > > format.
> >     > > > XR
> >     > > > > uses this format (for IPv6 at least). Nokia SROS uses this
> >     > > > > format.
> >     > > > >
> >     > > > > We have written a bunch of models where the lack of this IMHO
> >     > > > > makes
> >     > > > them
> >     > > > > less elegant. I'd like for there to be an IETF standard data type
> >     > > > > to make those models more elegant.
> >     > > > >
> >     > > > > Kind regards,
> >     > > > > Kristian.
> >     > > > >
> >     > > > > _______________________________________________
> >     > > > > netmod mailing list
> >     > > > > netmod@ietf.org
> >     > > > > https://www.ietf.org/mailman/listinfo/netmod
> >     > > >
> >     > > >
> >     > > >
> > > > >
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> >     > > >
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> >     > >
> >     > > --
> >     > > Juergen Schoenwaelder           Jacobs University Bremen gGmbH
> >     > > Phone: +49 421 200 3587         Campus Ring 1 | 28759 Bremen |
> > Germany
> >     > > Fax:   +49 421 200 3103         <https://www.jacobs-university.de/>
> >     > >
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